Model Engine Maker

Engines => Your Own Design => Topic started by: Vixen on August 30, 2019, 12:57:48 PM

Title: Bristol Mercury revisited
Post by: Vixen on August 30, 2019, 12:57:48 PM
Some years ago I built two 1/4 scale models of the Bristol Mercury MK VIII radial engine. One of the engines was displayed in an 'exploded' format so as to show both the external and internal details. The other engine has been assembled and one day will become a runner.

The 'exploded' Mercury was mounted on two display stands. One showed the external or outer components, such as the crankcase, the supercharger housing, the reduction gearbox housing etc. While the second display stand showed the internal workings, such as the crankshaft, conrods and pistons. In fact, the mechanisms from each of the engine's subsection was displayed individually and each was able to rotate to demonstrate it's function. The nine cylinders were distributed between the two display stands with outline drawings of the missing cylinders, where appropriate.

(http://lister-engine.com/coppermine/albums/userpics/10013/IMG_3327_1.JPG)

Here are the two display stands as they were exhibited at the 2010 Model Engineer Exhibition at Sandown Park. The Bristol Mercury was awarded the Bradbury Winter Trophy and a Gold Medal. A full write up on the displays can be found at http://modelengineeringwebsite.com/Bristol_Mercury_VIII.html. Click on any image and it will enlarge, click on it again to zoom right in and see all the detail.

Although the two display stands were award winners, I was never fully satisfied with them. Two stands required a lot of table space and storage. I also felt they divided the viewers attention between the two. So I decided I would try and combine the two display stands into one and still be able to tell the story of how each component worked as part of the whole engine.

I made a start by combining the accessories gearbox and drives into the rear casing of the engine. I still wanted to show the accessories gearbox.in the 'exploded' format.

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070468.JPG)

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070469.JPG)

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070470.JPG)

As you can see the accessories gearbox is a complex affair. The inertia starter motor is attached to the rear face. The interrupter gear, which prevents the machine guns from shooting off the propellor, sticks out of the top. The dual magnetos attach to either side and the pressure and scavenge oil pumps do likewise at a lower level. The long quill shaft takes the stater motor power into the heart of the engine and is also used to transmit engine power to drive all the accessories. it is possible to turn the quill shaft by hand which rotates all the internal gears and drive shafts.

The centrifugal supercharger drive were the next components to be combined.

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070472.JPG)

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070471.JPG)

The star shaped impeller and the spiral diffuser vanes can be seen at the rear of the supercharger core. On the other side is the 'speed up' gear train which spins the impeller at 7 times engine speed. The central gear is a 'spring gear' which cushions the high speed gears from any engine crankshaft  fluctuations.

There is a lot more work still to be completed. The biggest challenge being a new central  clear perspex panel to display all nine cylinders, pistons conrods, crankshaft within one half of the crankcase housing.

Hope you will like the new display

Mike
Title: Re: Bristol Mercury revisited
Post by: steamer on August 30, 2019, 01:49:12 PM
 :o :AllHailTheKing:

Oh man that is beautiful work Mike!   Are you getting finished detail drawings of the original to start with, or are you taking pictures and diagrams and making the drawings yourself?

Dave

Title: Re: Bristol Mercury revisited
Post by: b.lindsey on August 30, 2019, 02:03:09 PM
Totally awesome Mike!!  Wow!!

Bill
Title: Re: Bristol Mercury revisited
Post by: Johnmcc69 on August 30, 2019, 02:55:12 PM
What a beautiful display! I look forward to your progress with it.

  :ThumbsUp: :popcorn:

 John
Title: Re: Bristol Mercury revisited
Post by: Old Bill on August 30, 2019, 03:17:18 PM
Hi Mike.

I must admit that I do like your display. This is such a complex engine that when assembled, one cannot appreciate the work involved and it is wonderful to be able to see how it works. The only down side is that you had to make two! I look forward to seeing it again in its new incarnation.

What do you do in your spare time?

Steve     :ThumbsUp:
Title: Re: Bristol Mercury revisited
Post by: Vixen on August 30, 2019, 03:18:52 PM
  Are you getting finished detail drawings of the original to start with, or are you taking pictures and diagrams and making the drawings yourself?

Dave

I have the Works handbook for this engine. I contains over 30 small size copies of the original builders blue prints. They are highly detailed and very accurate. I have digitised these into AutoCAD and have produced a full set of model part drawings form them. There must be several thousand piece parts in that engine. I have also had complete access to photograph stripped down Mercury Mk VIII engines at ARC at Duxford. So no excuses for lack of detail.

Mike
Title: Re: Bristol Mercury revisited
Post by: Vixen on August 30, 2019, 03:22:39 PM

What do you do in your spare time?

Steve     

Steve, I don't have any spare time, I'm retired. :old:

I was busy building  these two Bristol Mercury engines when we worked together, and that was a long time ago.

Mike
Title: Re: Bristol Mercury revisited
Post by: Jo on August 30, 2019, 04:51:48 PM
The sectioned Mercury always went down well with the public at shows, you will have to starting bringing it out again  8)


What do you do in your spare time?

Steve     

Steve, I don't have any spare time, I'm retired. :old:

I was busy building  these two Bristol Mercury engines when we worked together, and that was a long time ago.

I agree being retired does not mean you get any spare time  :disappointed: :toilet_claw:

Mike thought you were working on your ploughing engine back then :noidea:

Jo
Title: Re: Bristol Mercury revisited
Post by: Roger B on August 30, 2019, 05:36:43 PM
That is a splendid display  :praise2:  :praise2: I would like to see it for real one day  :)  :wine1:
Title: Re: Bristol Mercury revisited
Post by: Vixen on August 30, 2019, 05:56:28 PM
The sectioned Mercury always went down well with the public at shows, you will have to starting bringing it out again  8)
Mike thought you were working on your ploughing engine back then :noidea:

Jo

I took/ take the Mercury to all the indoor shows I can get too. Unfortunately they are now very few in number, now that Guildford, Bristol and the MEX at Sandown have all stopped.

I started the Mercury engines and drawing more than 20 years ago, I cannot remember precisely when Steve left us.. The Fowler Plowing Engine was started back in the mid 1980's soon after I moved to Hampshire and set up my first ever machine shop.

Mike
Title: Re: Bristol Mercury revisited
Post by: Ye-Ole Steam Dude on August 30, 2019, 06:42:39 PM
Hello Mike,

Incredible work and a wonderful display.

Have a great day,
Thomas
Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on August 30, 2019, 09:11:23 PM
Wow - jaw dropping .... Mike do you EVER do things the easy way ...?... or for that matter have any small projects ...  :thinking:
Title: Re: Bristol Mercury revisited
Post by: Vixen on September 02, 2019, 04:19:48 PM
.... Mike do you EVER do things the easy way ...?... or for that matter have any small projects ...  :thinking:

Per; Every big project is really a series of small projects joined together.      As for easy... what's the challenge in that?.



There are some more photos of the Mercury supercharger assembly.

The supercharger's outer cover was a single casting on the full size engine, I machined mine from solid, as you can guess, there was not much left of the billet when I had finished, it did produce a bucket full of chips.

In these photos you can see the machined from solid rear cover, the machined from solid carburettor inlet manifold and the nine lost wax cast outlet manifolds which feed the fuel mixture to the nine cylinders, two pipes per cylinder. The copper pipework is part of the fuel priming system used during engine start up. The bearing in the center of the unpainted cover disc, supports the quill shaft for the Accessories Gearbox, featured in the first post of this topic.

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070509.JPG)

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070510.JPG)

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070512.JPG)


The supercharger drive gearbox with the star shaped impeller and diffuser fits inside the rear cover to form the outer annular space (plenum chamber) which feeds the outlet ports.

The fuel mixture from the double barreled, updraft, carburetter enters the bottom of the supercharger at the rear. The fuel mixture spirals inside the rearcover into the centre hole, where it enters the eye of the fast rotating impeller. The fuel mixture if flung outwards at high velocity into the diverging diffuser ducts. The airflow velocity is slowed down in the diffuser ducts, which convert the velocity change into a pressure change. The pressurised fuel mixture collects in the outer annular plenum chamber and is distributed equally to the nine cylinders.

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070514.JPG)

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070515.JPG)

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070519.JPG)

The supercharger assembly forms a very compact unit which bolts to the rear of the engines crankcase by the same nine bolts which hold the two halves of the crankcase together

I am proposing to keep the two halves of the supercharger separated on the display stand, so that the internal workings can be seem and explained.

Mike



Title: Re: Bristol Mercury revisited
Post by: Vixen on September 06, 2019, 07:28:51 PM
Some more work combining the two 1/4 scale Bristol Mercury display stands into one.

The next section to receive attention was the Cam Gear, which is located at the front of the front Crankcase half. The circular cam barrel is driven from the crankshaft via an eight to one gear reduction; it rotates coaxialy around the crankshaft, but in the opposite direction. There are two cam rings, the forward one operates the inlet valve pushrods and the rear one the exhaust push rods. Each cam ring has four lobes which act against a total of eighteen roller cam followers.

As you can see, the Cam Gear is very compact and neatly integrated into the front half of the crankcase.

In the working engine, the bearings for the intermediate gears of the eight to one reduction.gear train, are part of the adjoining thrust plate. I had to make a small perspex bracket to support the bearings for this exploded display.

That twenty tooth wheel in the centre, is the splined coupling which connects the crankshaft to the reduction gearbox, located at the very front of the engine. I will get to explain the reduction gearbox a little later.
 
(http://lister-engine.com/coppermine/albums/userpics/10013/P1070473.JPG)

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070475.JPG)

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070476.JPG)


I decided to make a start on the new central perspex panel, which will eventually support the cylinders, pistons, conrods and crankshaft. The new clear perspex panel measures 19" by 16 " and is 8 mm thick. I knew it was going to be a fight to machine all of the cutouts on my small mill. It has a total travel of only 8" x 4". but this was just enough.  The panel needed to be carefully positioned for each cutout, as the confines of the machines cabinet only added to the fun and games. Eventually, I was able to machine about 80% of the features and completed the remainder with a saw and hand files.

The intention is to have the bottom four cylinders bolted to the crankcase while the upper five cylinders are displaced outwards to reveal the workings of the master and slave conrods.

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070481.JPG)

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070528.JPG)

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070529.JPG)

The biggest drawback with machining and handworking perspex is the enormous amount of fluffy white swarf it produces. The only answer is to have the Vacuum extracting the fluff and dust continuously. A very noisy process.

Mike

Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on September 06, 2019, 09:53:02 PM
Quote
Quote from: Admiral_dk on August 30, 2019, 10:11:23 PM
.... Mike do you EVER do things the easy way ...?... or for that matter have any small projects ...  :thinking:

Per; Every big project is really a series of small projects joined together.      As for easy... what's the challenge in that?.

OK - I admit, that was the wrong question ..... probably because most of my constructions are meant to go into production, where simpler (usually) => the smaller amounts of errors and time consumed => less cost, etc.

I look forward to see the end result  :cheers:   :popcorn:
Title: Re: Bristol Mercury revisited
Post by: Vixen on September 06, 2019, 11:33:18 PM
Hello Per,

You make a very good point about production v simplicity = minimum errors, least time and lowest cost etc.

I believe Henry Ford's design philosophy was "simplify and add lightness". The Ford Motor Company didn't do too badly.

Sir Roy Feddon, Bristol's chief engineer, had an entirely different view, he loved complexity and elaboration in his engines. He could not leave a design alone, he always wanted to change and 'improve' it. He nearly bankrupted the Bristol Aircraft Company, before they eventually sacked him. I have always been fascinated by the man and his over complex engines. That's why I build so many of them.

For a successful business, "time is money", however, when you are retired "time is for pleasure"

Mike
Title: Re: Bristol Mercury revisited
Post by: Jo on September 07, 2019, 06:21:03 AM
For a successful business, "time is money", however, when you are retired "time is for pleasure"

I prefer to think that in retirement that "both Time and Money are finite" the trick is to make sure one doesn't run out before the other and to make the most of both of them  ;)

Jo
Title: Re: Bristol Mercury revisited
Post by: Vixen on September 08, 2019, 05:47:10 PM
So back to the plot. It's time to put away the history books and look at progress with the new Bristol Mercury VIII display stand.

The new central display panel will mount all nine cylinders and the crankshaft assembly. Here you can see the crankshaft assembly. The difference in robustness of the master rod compared to the eight slave rods is quite noticeable. The single throw crankshaft is made of two pieces, which are bolted together at the rear by the large maneoton pinch bolt. The mass of the pistons and conrods is counterbalanced by adding weights to the  crankshaft. The weight on the rear half is slightly larger than the front to counteract the added weight of the maneoton bolt. At the front, is the splined coupling which drives the 2:1 reduction gearbox.

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070486.JPG)

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070490.JPG)



I have decided to bolt the lower four cylinders in place on the rear crankcase half and position the other five cylinders outboard, so that the interior details remain visible.

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070492.JPG)

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070495.JPG)



It was Bristol's practice to position the master rod in one of the lower cylinders, number 6. The lower cylinders are always more oily than the others, due to gravity. The master rod does it's own share of the work plus a small contribution of work from each the other eight cylinders and so benefits from the additional lubrication.

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070497.JPG)

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070498.JPG)



This is the new central panel with all nine cylinders attached. The pistons for the five upper cylinders are guided by clear perspex shoes running in radial slots. The whole assembly will rotate to demonstrate the fluid motion of the nine pistons but at the moment it is very stiff. I am trying to avoid the use of any oil, because it dries out over time and is bound to leak, just like any other radial engine.

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070531.JPG)

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070532.JPG)



I am pleased with how this new symmetrical display has turned out. There is still work to be done with the cam gear and reduction gearbox sections but they should not take too much effort. Then everything needs to be taken apart, cleaned dusted and polished before the final assembly.

Mike

Title: Re: Bristol Mercury revisited
Post by: Vixen on September 09, 2019, 08:19:33 AM
A new topic titled "The other Bristol Mercury engines" has been specially created  for discussions relating to the Mercury engine's background and history.

Mike
Title: Re: Bristol Mercury revisited
Post by: sco on September 09, 2019, 12:20:01 PM
Terrific pictures of the new display layout Mike - would love to see it in the flesh too!

Simon.
Title: Re: Bristol Mercury revisited
Post by: Vixen on September 09, 2019, 12:37:17 PM
Hello Simon,

We need to arrange a visit to you up in Brackley.

Mike
Title: Re: Bristol Mercury revisited
Post by: Craig DeShong on September 09, 2019, 11:21:36 PM
Mike

I open ALL your new posts and read and look through them but I usually close them without making a comment.  I do this, not because I have no comment to make, but because they always leave me speechless. 

I have no words to describe the caliber of work I see in your posts, but I do enjoy reviewing them.  Thanks for bringing them here for me (and us) to enjoy.
Title: Re: Bristol Mercury revisited
Post by: Vixen on September 10, 2019, 08:19:46 AM
Hello Craig,

Thanks.  :ThumbsUp: :ThumbsUp: :ThumbsUp:

Model engineering is very important to me. It gives me immense pleasure and satisfaction and somewhere to go when life gets tough. I feel lucky to be able to share what I do, with you guys and gals on the MEM forum. It's the membership of the MEM forum who make it such a very special place to hang out.

Mike
Title: Re: Bristol Mercury revisited
Post by: Johnmcc69 on September 10, 2019, 02:52:34 PM
 :ThumbsUp:
 Outstanding work Mike! Really going to be a spectacular display!

 John
Title: Re: Bristol Mercury revisited
Post by: Vixen on September 11, 2019, 02:41:22 PM
Thanks John,

The final part of the Bristol Mercury jigsaw is the propellor speed reduction gearbox, which is mounted at the very front of the engine. The 2:1 reduction is achieved in a compact bevel, epicyclic gear set. The large bevel gear at the front, is rigidly bolted to the bell shaped outer cover and does not rotate. The large bevel gear at the rear is rotated by the engine's crankshaft via the splined coupling. The three smaller bevel pinions rotate the splined propeller shaft at half the speed of the crankshaft. The 2:1 speed reduction allowed a much larger diameter and therefore more efficient propeller to be used. The large diameter thrust bearing at the very front, transmits the whole of the propellers thrust into the bell shaped cover. The engines crankshaft does not see any of the propeller's thrust force.

The normal cruising speed for the Mercury Mk VIII was 2400 RPM, while the maximum speed (at takeoff boost) was 2650 RPM. The actual propellor speed being half of that.

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070542.JPG)

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070543.JPG)


For the 'exploded' display, I did not want to hide the reduction gears within the bell shaped cover, in there, it would have been completely out of sight. I decided to manufacture a completely new perspex front upright, so that the reduction gearbox could be displayed immediately below the bell shaped outer cover.

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070541.JPG)


This is how the front of the new display turned out. A few weeks work has completely transformed the 'exploded' display.
That's my other big radial engine, the 1/3 scale Bristol Jupiter in the background

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070552.JPG)


There are still one or two bits to sort out, but the majority of the changes to the 'exploded' Bristol Mercury Mk VIII display have now been completed. My wife and I are about to depart for a late summer holiday to belatedly celebrate our 50th wedding anniversary. I will quickly finish the Mercury display when we return, then it's back to work on the Jupiter engine.

Mike




Title: Re: Bristol Mercury revisited
Post by: AVTUR on September 11, 2019, 03:40:41 PM
Mike

Have a good holiday. I think you need it after such a tour de force.

AVTUR
Title: Re: Bristol Mercury revisited
Post by: cnr6400 on September 11, 2019, 06:57:36 PM
Outstanding work Mike, well done!  :ThumbsUp: :ThumbsUp: :ThumbsUp:
Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on September 11, 2019, 10:07:38 PM
Enjoy the holiday with the missus Mike  :cheers:

I really think you dramatically improved the display of you fantastic build here - before it was almost two not related engines, and now it really appears as a single unit - just slightly "exploded" to allow an inside peak  :whoohoo:

Per
Title: Re: Bristol Mercury revisited
Post by: Steamer5 on September 12, 2019, 05:46:39 AM
Hi Mike

That’s just jaw dropping......

Cheers Kerrin
Title: Re: Bristol Mercury revisited
Post by: steamer on September 12, 2019, 02:08:54 PM
Thanks John,

The final part of the Bristol Mercury jigsaw is the propellor speed reduction gearbox, which is mounted at the very front of the engine. The 2:1 reduction is achieved in a compact bevel, epicyclic gear set. The large bevel gear at the front, is rigidly bolted to the bell shaped outer cover and does not rotate. The large bevel gear at the rear is rotated by the engine's crankshaft via the splined coupling. The three smaller bevel pinions rotate the splined propeller shaft at half the speed of the crankshaft. The 2:1 speed reduction allowed a much larger diameter and therefore more efficient propeller to be used. The large diameter thrust bearing at the very front, transmits the whole of the propellers thrust into the bell shaped cover. The engines crankshaft does not see any of the propeller's thrust force.

The normal cruising speed for the Mercury Mk VIII was 2400 RPM, while the maximum speed (at takeoff boost) was 2650 RPM. The actual propellor speed being half of that.

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070542.JPG)

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070543.JPG)


For the 'exploded' display, I did not want to hide the reduction gears within the bell shaped cover, in there, it would have been completely out of sight. I decided to manufacture a completely new perspex front upright, so that the reduction gearbox could be displayed immediately below the bell shaped outer cover.

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070541.JPG)


This is how the front of the new display turned out. A few weeks work has completely transformed the 'exploded' display.
That's my other big radial engine, the 1/3 scale Bristol Jupiter in the background

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070552.JPG)


There are still one or two bits to sort out, but the majority of the changes to the 'exploded' Bristol Mercury Mk VIII display have now been completed. My wife and I are about to depart for a late summer holiday to belatedly celebrate our 50th wedding anniversary. I will quickly finish the Mercury display when we return, then it's back to work on the Jupiter engine.

Mike

Epicyclic tooth form!.....wow!    That's unusual for power transmission...at least to me over the last 35 years....  Why that form do you know?

Dave
Title: Re: Bristol Mercury revisited
Post by: Vixen on September 12, 2019, 04:44:40 PM
Thanks everyone for calling in and for your generous comments.

Dave,

The bevels are standard straight cut bevel gears, nothing special. They are arranged to form a very compact epicyclic gear reduction set. If you study the layout closely, you will be able to see the input bevel is the sun, the three pinion bevels are the planets and the fixed bevel in the front is the annulus. You may need a bit of imagination, as the epicyclic function  is folded in upon itself; but it's there and it works.

This form of bevel gear reduction was used on all the Bristol radial engines from the Jupiter through to the mighty Centaurus. It was light, very compact and very reliable. The 2:1 reduction was the most common, but other reduction ratios were available to match different aircraft performance requirements, by changing the tooth count.

Cheers

Mike
Title: Re: Bristol Mercury revisited
Post by: steamer on September 12, 2019, 07:45:12 PM
Ahh    not tooth form but gear arrangement.    I think I understand now

Dave
Title: Re: Bristol Mercury revisited
Post by: Roger B on September 20, 2019, 11:36:37 AM
Mike, excellent work as ever  :praise2:  :praise2: This type of folded epycyclic (like a differential gear set) was used in the Automotive Products automatic transmission. Some details are given here:

http://www.austinmemories.com/styled-105/index.html
Title: Re: Bristol Mercury revisited
Post by: Vixen on October 05, 2019, 12:50:24 PM
Sonia and I celebrated our 50th wedding anniversary with a ten day tour around the old Imperial capitals of central and eastern Europe. We visited Prague in the Czech Republic<, Vienna in Austria, Budapest in Hungary and Nuremberg in Germany. The old Imperial splendour was still there, it had survived the ravages of the the 20th century, world wars and in some cases, the Communist regime. Budapest was by far the most impressive of all the cities we visited. Today the splendours of yesterday are slowly being submerged by modern concrete and hi-rise development. But, I guess it's the same everywhere.

I have been able to put the finishing touches to my revised display stand for the 'exploded' Bristol Mercury Mk VIII radial engine.

I used a new sheet of smoke tinted Perspex to form the base of the display. I layed a copy of an original blueprint under the Perspex base to add interest.

I attached full size copies of the three data plates to the wooden surround. These data plates can also be seen, in their miniature form, mounted on top of the Thrust Bearing Housing, immediately behind the Reduction Gearbox Casing.

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070623.JPG)


Here you can see the main engine data plate. I built my replica engine as a model of engine serial number M 40614 which was originally completed in May of 1937 (82 years ago). You can read the engines vital statistics for yourself.

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070617.JPG)

Here is the completed display stand, all dolled up but with nowhere to go.

Model Engineering Exhibitions may be disappearing, a thing of the past, but fortunately, we still have MEM, where we can still enjoy a virtual model show.

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070624.JPG)

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070625.JPG)

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070626.JPG)

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070627.JPG)

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070628.JPG)


I am pleased with how the revised display stand has turned out. The single display is much more compact and tells the story much better than before. It is also so much easier to transport, display and store one item than two. Some of the intricate gear mechanisms are not so clearly visible as before but overall I think it does a better job of displaying the engineering genius of Roy Fedden, the Bristol Aircraft Company and a bygone era of aviation history.

(http://lister-engine.com/coppermine/albums/userpics/10013/P1070629.JPG)

Now, it's back to the Bristol Jupiter

Mike

Title: Re: Bristol Mercury revisited
Post by: Jo on October 05, 2019, 02:18:35 PM
 8) Nice.

I must come and visit so I can see your new display in person Mike  :embarassed:

Your "blue print" I hope it is LaserJet printed so it won't fade over time  :ThumbsUp:

Jo
Title: Re: Bristol Mercury revisited
Post by: Jasonb on October 05, 2019, 02:36:12 PM
Looks impressive Mike, will you be displaying it at the Midlands show in a couple of weeks?
Title: Re: Bristol Mercury revisited
Post by: Vixen on October 05, 2019, 02:53:19 PM
Looks impressive Mike, will you be displaying it at the Midlands show in a couple of weeks?

Hello Jason,

No, I don't think so.
Ask Jo about the welcome I received from the organisers at last year's Midlands show

Mike
Title: Re: Bristol Mercury revisited
Post by: Vixen on October 05, 2019, 02:55:02 PM
8) Nice.

I must come and visit so I can see your new display in person Mike  :embarassed:

Your "blue print" I hope it is LaserJet printed so it won't fade over time  :ThumbsUp:

Jo

Your always welcome Jo.

And yes it is a laser print, not a real blue print smelling of cat's pee.

Mike
Title: Re: Bristol Mercury revisited
Post by: steamer on October 05, 2019, 03:14:43 PM

Yes...the pea smell is from a Diazo copy, which is special sensitive paper that develops with ammonia.    Used one of those for a few years.   The prints are made by laying a vellum original on top of the paper and running it through the machine which then spitted out the pair, you put the original away and take your copy....it's more like a blueish background....not like a blue print.   You could also get the special paper in pink.   We would use that paper for parts that were going through the shop the first time.   If you saw a "Pink print" you knew that the manufacturing process and the design was new and subject to change.

Dave

Title: Re: Bristol Mercury revisited
Post by: steamer on October 05, 2019, 03:24:00 PM
Mike

That's one of the most beautiful things I've ever seen.       Wow!

Dave
Title: Re: Bristol Mercury revisited
Post by: sco on October 05, 2019, 04:39:24 PM
Incredible piece of artwork Mike - as Dave said, Wow!

Simon.
Title: Re: Bristol Mercury revisited
Post by: AVTUR on October 05, 2019, 06:19:59 PM
Mike

Magnificent! Does Fedden proud.

I will copy the pictures and show the lads at work, Bristol RRHT, in the next couple of weeks.

Budapest is a good, fine city. I went there for a long weekend in 1991.

AVTUR
Title: Re: Bristol Mercury revisited
Post by: Johnmcc69 on October 05, 2019, 07:53:20 PM
Museum quality! I like the "old" blueprint in the base.
 :NotWorthy:
 John
Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on October 05, 2019, 08:28:57 PM
Fabolous exhibit - absolute museum quality  :praise2:

Considering how much time you apply to the engines you build - I think that you and the missus did a somewhat superficial tour of those nice cities - or perhaps better said this way :

Both those cities and you both deserved a longer stay  ;)  - congratulations  :cheers:  and best wishes

Per
Title: Re: Bristol Mercury revisited
Post by: fumopuc on October 05, 2019, 08:46:41 PM
Yes Mike, it is a masterpiece.
The engine and the 50th wedding anniversary.
Title: Re: Bristol Mercury revisited
Post by: kvom on October 05, 2019, 09:09:34 PM
My wife and I were in Nuremberg for a day 2 weeks ago.  Mayhaps we passed in the crowd.
Title: Re: Bristol Mercury revisited
Post by: Roger B on October 06, 2019, 07:53:31 AM
Absolutely splendid  :praise2:  :praise2:  :wine1: With the demise of UK Model Engineering shows have you considered the European ones such as Faszination Modellbau?

https://www.faszination-modellbau.de/en/faszination-modellbau/
Title: Re: Bristol Mercury revisited
Post by: fumopuc on October 06, 2019, 10:04:24 AM
Absolutely splendid  :praise2: :praise2: :wine1: With the demise of UK Model Engineering shows have you considered the European ones such as Faszination Modellbau?

https://www.faszination-modellbau.de/en/faszination-modellbau/ (https://www.faszination-modellbau.de/en/faszination-modellbau/)


I will try to do my visit there this year at the very first day, Friday.
Title: Re: Bristol Mercury revisited
Post by: Vixen on October 06, 2019, 12:10:05 PM
Thank you all for looking in and for the generous comments, they are always very rewarding.

Admiral; We are already planning a longer and more leisurely holiday in Budapest.

kvom; I saw another guy in Nuremberg with obvious workshop withdrawal symptoms, could that have been you?

Roger; The big European shows such as Faszination Modellbau are massive exhibitions, bigger than anything we have in the UK. I would like to get to one, one day. If I were to display an engine, it would mean a very long road or rail journey, my models are too big to fit into a suitcase, so flying is out.

Mike
Title: Re: Bristol Mercury revisited
Post by: Jo on October 06, 2019, 12:24:36 PM
Roger; The big European shows such as Faszination Modellbau are massive exhibitions, I would like to get to one, one day. If I were to display an engine, it would mean a very long road or rail journey, my models are too big to fit into a suitcase, so flying is out.

Sadly after the end of the month you might find you have to fill in a load of customs paperwork and probably pay for the honour as well   :rant:

Jo
Title: Re: Bristol Mercury revisited
Post by: Art K on October 06, 2019, 09:05:07 PM
Mike,
Sorry to be jumping on the train late BUT, that is some fabulous work there and hopefully I will get to the UK some day to see it in person. One can always hope. Yes, Vienna and Budapest are great cities to visit but try not to drive in the latter. If you miss a turn the streets are all one way the wrong direction. :wallbang:
Art
Title: Re: Bristol Mercury revisited
Post by: mike mott on October 06, 2019, 09:54:36 PM
Always great to see not only a beautifully crafted piece of model engineering, but also an excellent way to display it.

Mike
Title: Re: Bristol Mercury revisited
Post by: Dave Otto on October 07, 2019, 12:15:02 AM
I was going to reply yesterday and couldn't think of what to say except for beautiful job, which doesn't seem like nearly enough for a project of the scope and the amazing outcome.
Anyway the time, effort, skill, and craftsmanship that you have put into this project clearly shows.

What an amazing piece of work!
Dave

 
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 12, 2019, 11:21:13 PM
Part 2       The second Bristol Mercury

When the supercharged Bristol Mercury Mk VIII was introduced in 1935 it was rated at an impressive 840 BHP all the way from sea level to 14,000 feet. An impressive performance from a comparatively small engine. Engine development had by now outgrown the wooden propellers of earlier engines. The Bristol Mercury MK VIII was fitted with a 12 foot diameter three blade, all metal, propeller with controllable variable pitch. The propeller was a first generation variable pitch propeller with only two pitch settings, Fine pitch for take off and landings, and a course pitch setting for economical cruising.

(https://lister-engine.com/coppermine/albums/userpics/10013/p1250439small~0.JPG)

This photo shows the three blade De Havilland all metal propeller fitted to a Bristol Mercury. The aircraft is the Bristol Blenheim light bomber, restored by the ARC at Duxford UK.

The large cylinder, pointing forward in the propeller hub is the spring assisted hydraulic cylinder which moves the three propeller blades to the fine pitch (a blade angle of 14 *) for take off. The three heavy bob weights move outwards, due to centrifugal force, as the engine revs are increased. They move the three blades to the course pitch (a blade angle of 34*) . The pilot can control the timing of pitch change, during climb out, with the pitch control lever, The lever releases the oil pressure in the central cylinder allowing the blades to move to the course setting. Before landing, the pilot moves the pitch control lever to 'fine' and the engine pumps lubricating oil back into the central cylinder to force the three blades back to the fine pitch setting prior to a landing.

My second Mercury engine is intended to be a runner and so will require a suitable propeller. I am planning to build a 1/4 scale De Havilland variable pitch propeller for the second engine. At 1/4 scale, the three blade propeller will be 36" in diameter. A propeller of that size is required to provide an adequate load for the engine but is very large, unwieldy and inconvenient when displaying the engine at exhibitions, so I have decided to fit three short 'stub' blades for exhibition purposes and replace them with the full length blades when the engine is to run.

(https://lister-engine.com/coppermine/albums/userpics/10013/Bristol_Mercury_VP_Prop-1010~0.jpg)

Bristols did the same, back in the thirties, and fitted short stub blades to the full size engines they displayed (for sale) at air shows such as Farnborough and the Paris Salon

Stay tuned and watch the chips fly

Mike
Title: Re: Bristol Mercury revisited
Post by: Craig DeShong on November 12, 2019, 11:32:48 PM
Mike, I can hardly contain my excitement at the announcement  of this new build.  It’s going to provide many hours of pleasure for you readers.  I’m getting the popcorn ready as I post this.   :popcorn: :popcorn: :popcorn:
Title: Re: Bristol Mercury revisited
Post by: Steamer5 on November 13, 2019, 08:15:53 AM
Hi Mike,
 Make that 2 !
Planting season here & the pop corn is growing! Not much of last years left, hope I get a good crop as it looks like I’ll need it!

Cheers Kerrin
Title: Re: Bristol Mercury revisited
Post by: mike mott on November 13, 2019, 03:12:54 PM
Mike I will follow along as well, I am still mind boggled by the first one and the way that you have exhibited it. Being able to watch and share such work being developed and made is one of the great things about the modern internet, and sites like this excellent one!

Mike
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 13, 2019, 09:34:32 PM
Thanks for calling in guys.

The first part to be made for the 1/4 scale De Havilland Variable pitch propeller is the Hub Barrel, which houses the blade rotation mechanism and the blade thrust bearings.

The full size Hub Barrel consists of a pair of precision forging which are bolted together during assembly. I started with two 3" x 3" X 1" thick slabs of HE 30 grade (6082).extruded aluminium alloy. Six dowel pins and a central bolt were used to locate and secure the stock to my well used sacrificial jig plate. The first operation was to mill the basic outline profile using a conventional end mill. The curved shape was then created with a 4mm ball mill. The ball mill traced out numerous toolpaths, like the height contours on a map, to form the rough three dimensional shape. The spacing of the contours is always a compromise, very close contours result in a smoother object at the cost of hours of extra machining time. The roughed contours can be cleaned up later by filing to clean up the machining and to smooth out the contour ridges

Here you can see the front half being profiled with the 4mm ball cutter, in stages

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070647.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070648.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070649.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070650.JPG)


The centrol hold down bolt was removed so that the centre through hole could be machined

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070651.JPG)


The whole exercise was repeated for the rear half, using a slightly modified toolpath program, to form the flange on the rear face

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070643.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070645.JPG)

The shape of the Hub Barrel becomes clearer when the two halves are bolted together. The next stage will be  to machine the three propeller blade root details, followed by lots of hand filing to clean up the machining and to smooth the contour ridges

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070652.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070653.JPG)

I learned a lesson, the hard way, regarding the cutting conditions of a ball mill when profiling a curved surface. Initially, the ball mill contactes the stock material with it's outer edge (full diameter). The feeds and speeds need to be similar to those for a conventional end mill. However as the contours approach the upper surfaces, the point of contact moves form the outer edge towards the centre line of the ball mill. The actual cutting speed gradually reduces as the point of contact approaches the centre line of the ball cutter. and is effectively zero on the centre line. Also the size of the flutes, needed to carry away the swarf, also reduce in size. I learned the hard way, that the feeds and speeds need to be progressively adjusted to cater for the different cutting conditions.

Look at this unfortunate four flute ball cutter. If I had been paying more attention and if I had increased the spindle speed and reduced the feed rate at the appropriate time, I may have prevented this cold welding and clogged flutes. Lesson learned.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070691.JPG)

Stay tuned

Mike
Title: Re: Bristol Mercury revisited
Post by: crueby on November 13, 2019, 09:38:22 PM
Fascinating work, following along here as well!   :popcorn: :popcorn: :popcorn:

And that clogged ball end cutter would make a great modern-art exhibit...!
Title: Re: Bristol Mercury revisited
Post by: deltatango on November 13, 2019, 11:12:54 PM
Following and watching in awe!

The hint regarding ball-ended milling cutters has gone into the memory banks - hope it can be retrieved when needed.

David
Title: Re: Bristol Mercury revisited
Post by: mike mott on November 13, 2019, 11:45:44 PM
Mike was the cutting done with cnc or by the hand dials? impressive bit of machine work.

Mike
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 13, 2019, 11:57:36 PM
Mike

Other than the tailstock on the lathe, I do not have any other hand wheels, all my machines are CNC.

I guess if I had been turning the hand wheels by hand, I would have felt the cut and would not have over driven that unfortunate ball cutter.

Mike
Title: Re: Bristol Mercury revisited
Post by: john mills on November 14, 2019, 07:44:42 AM
was that a carbide ball nose end mill and what speed and feed were you you able to drive it at.
and are you able to use coolant  ?are you able to use coolant at high pressure and good flow.
It is always satisfying to see these shapes form when cutting on cnc machines.
I am following your projects with great interest .it must of been interesting to see factories processes making the
full size engine parts , the way they went about the machining at that time.

John   
Title: Re: Bristol Mercury revisited
Post by: Jasonb on November 14, 2019, 09:06:04 AM
Off to a good start Mike.

Have you thought about using corner radius cutters rather than ball nose ? They keep the cutting speeds about the same and you get better chip clearance, would also have left the tops of the lugs flat. I have always preferred them on the manual mill as they remove metal far quicker so seemed obvious to use them on the CNC
Title: Re: Bristol Mercury revisited
Post by: AVTUR on November 14, 2019, 09:34:49 AM
Mike

How long did it take you to machine the Hub Barrel?

I know you use CNC but if I was doing, not having CNC, it would take me a month of Sunday’s.

AVTUR
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 14, 2019, 10:37:56 AM
John,

You are correct, it is a four flute carbide ball nose end mill. I have never learnt how to get the best from carbide tooling, so I prefer HSS. Perhaps that's because I do not have a high speed spindle or any form of pumped coolant to cool, lubricate and flush the chips. I usually cut dry, using low pressure air, a paint brush or the occasional squirt of WD40. My carbide cutters do not seem to stay sharp for very long and then they become prone to pick up and cold welding. My feed and speed rates are probably too conservative.  I still have lots to learn.

Model engineers often have to carve/create the external 3 dimensional shapes to represent a casting or forged item, It's a problem the original manufacturer never faces.

I have a very old book which shows how Bristol's manufactured the Mercury engines back in the 1930's. The factory was filled with large, carefully selected, single purpose machines, set up to do one and only one process; for all their working life. They had a dedicated cylinder boring machines with a dedicated operators. Their sole purpose was to produce accurate 5.75" bores in the cylinder forgings, week after week, month after month. I am sure they got realy good at it, with all that practice.

Next to the cylinder boring station was the lathe like machine which cut the cooling fins. Another robust single purpose machine which cut all 15 cooling fin slots in one go, using a long bank of 15 parting tools, it looked like a huge hair comb. Next door to that, was the multi spindle drilling machine which simultaneously drilled the 8 bolt holes in the base flange.

Thats a far cry from our small multipurpose hobby machines which are expected to do everything, milling, drilling, gear cutting and much more.

Jason,

If I were to do that machining operation again (heaven forbid), I would do it completely differently. I needed the 4 mm cutter to form the corner radius for the six lugs. I should then have changed to a larger diameter cutter to do the upper part. A larger, two or three flute cutter would have better chip clearance than the tiny 4 mm ball nose cutter. In hindsight I would also have changed the feed/ speeds for the upper part of the Hub Barrel.

I have never seen (except in one of your videos) a corner radius cutter, I have certainly never used one. I can see the obvious advantages you describe. What is the correct name for these cutters and where do you buy them from? I am guilty of always trying to make do with what's to hand rather than shelling out lots of money on new kit.

Another problem I encountered was with my CAM program. For some unexplained reason (probably operator error) it decided to produce a conventional milling toolpath for a few of the contours and the preferred climb milling for the majority. The tool melt down occurred during one of the  conventional direction contours. I would have corrected the toolpath direction if I were to make another one.

Contouring with a ball nose mill will always be a roughing process requiring hand finishing to achieve the casting/ forging look.

ATUR,

The real cost in time was in producing the toolpath program, that took several days of work. Each Hub Barrel half was machined in about four or five hours. Doing that much toolpath work for single item is not very cost effective. It would be a small price to pay for a large batch of identical parts, but for a one off prototype, no. It's still quicker (and safer) than doing it all by hand.

Mike

Title: Re: Bristol Mercury revisited
Post by: sco on November 14, 2019, 11:16:01 AM
Corner rounding end mill:

https://www.cutwel.co.uk/milling/milling-cutters/hss-co8-milling-cutters/4-flute-hss-co8-corner-rounding-end-mill-weldon-e2498-series (https://www.cutwel.co.uk/milling/milling-cutters/hss-co8-milling-cutters/4-flute-hss-co8-corner-rounding-end-mill-weldon-e2498-series)

Following this project quietly...

Simon.
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 14, 2019, 11:42:56 AM
Hello Simon,

I have some of these concave corner rounding end mills. They are intended for breaking/ radiusing the edges of flat plate work.

Unfortunately they will not do as a substitute/ replacement for a ball nose end mill. For that we need a convex radius, like a conventional end mill with the corners ground off.

Still looking

Mike

Title: Re: Bristol Mercury revisited
Post by: john mills on November 14, 2019, 12:16:57 PM
I  have used and programmed old machines that i too used low speeds 3600 top speed and mortar feeds and ordinary coolant but mostly worked on tough tool steel .latter i run and programmed a smaller light weight machine with had a 10000 rpm spindle ,Ifound it worked best with light cuts and high speed 4mm would have been at full speed possibly 1meter minute feed but i think the coolant supply at good pressure  got to the cutting edge and that made it work.
Only thing i would do is rough with bigger tools possibly 10mm ball nose and use the smaller cutter for the finish.
that depends on the cad cam program you have and at slow speeds it could take a lot of time.
I have thought dedicated machines and opperator as you have said would be the way it would have to be done
with the tools available at that time .it must of been a job doing the same thing all the time but that was the way it was done.I worked with some one that did the same job for the war years re boring or sizing ford v8 con rods .
 
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 14, 2019, 12:48:38 PM
Hello John,

Better CAM software would certainly help in producing the toolpaths for different size cutters. I only have rather basic 2.5D CAD and CAM software, which can be slow work.

I considered a modern CAD/CAM package. Fusion 360 is well respected and (currently) free to the hobby user. But when I looked into it, I discovered the actual cost, to me, would be too high. First would be the cost of a modern, fast computer; which would throw me back into the clutches of Bill Gates and his over bloated WIN 10 nonsense. The second cost would be the time, lots of time, it would take to become  fast and proficient with the 3D CAD part and more time to become familiar and efficient with the CAM part of the package. Unfortunately time is one commodity us old guys do not have much left.

So I guess I will stick with my tried and trusted ancient 2.5D software, even though it's limited compared the clever stuff of a 3D package.

Mike
Title: Re: Bristol Mercury revisited
Post by: sco on November 14, 2019, 01:22:49 PM
Hello Simon,

I have some of these concave corner rounding end mills. They are intended for breaking/ radiousing the edges of flat plate work.

Unfortunately they will not do as a substitute/ replacement for a ball nose end mill. For that we need a convex radius, like a conventional end mill with the corners ground off.

Still looking

Mike

Sorry I completely misunderstood what you were trying to achieve  :-[

When I put 'corner radius cutter' into Google I only get the concave type - do you mean a lollipop cutter?

Simon.
Title: Re: Bristol Mercury revisited
Post by: Jasonb on November 14, 2019, 01:33:58 PM


Model engineers often have to carve/create the external 3 dimensional shapes to represent a casting or forged item, It's a problem the original manufacturer never faces.

Well maybe not in metal but the pattern maker had to!

The 4mm dia would not be a problem with say a 4mm x 1.0R cutter, I have mostly used 6mm dia but have used a 4mm on smaller parts where the internal corners needed the smaller fillet.

In the UK they are called Corner Radius Endmills but in the US they are known as Bull nose (not ball), Fusion has they already loaded in the tool libruary so easy enough to just pic the size and make any adjustments if it is not quite right or their speeds are too high. I have been using the ones from APT which are reasonable quality far eastern https://www.shop-apt.co.uk/corner-radius-end-mills-4-flute-altin-coated-carbide-45hrc.html

Even though coated I have not had build up problems brushing on a little paraffin and using air, going to rig something more permanent up soon.

I think I would have roughed with a square cornered aluminium specific cutter, then contoured with a 6mm x 1.0R and Fusion has the option to then go back and machine bits that the 6mm cutter could not get to with a smaller 4mm x 1.0R cutter, it will also work out a shallow stepdown on the flatter parts and more on near vertical ones.

I've just been playing with some insert tooling that would be good if you did not need such a small dia cutter and may use that a bit more for roughing out at 25mm dia and 5000rpm you can get the right sort of cutting speeds for aluminium and feed to suit. You can get the inserts with different corner radii just like the lathe inserts. 0.8R as standard.

If you want to send me a part file I'd be intereted to see what Fusion makes of it.
Title: Re: Bristol Mercury revisited
Post by: Jo on November 14, 2019, 01:41:45 PM
...we need a convex radius, like a conventional end mill with the corners ground off.

Still looking

I have a cutter grinder, you are welcome to use it Mike. It does what it says on the tin in the name   :)

Jo
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 14, 2019, 02:35:31 PM
Jason, Jo

Thanks for the link to the APT website for the Bull nose cutters. The corner radius (radii) are typically quite small , looks like the radii are intended as a protection for the cutting tip rather than for 3D contouring. I did see some 3mm R cutters which may prove useful.

I have recently bought a 12mm single insert end mill. It may be worthwhile for me to explore the availability of different tip radii and experiment a bit. However, I suspect they will all be small radii.

Alternatively I can take up Jo's kind offer and simply grind a larger radius on the outside of a conventional end mill. I believe a larger radius will produce the smoothest curved surfaces. So I now have plenty of options to consider.

Your description of the Fusion CAM package certainly shows what I am missing with my antiquated CAM software. For me it's a long slow process to generate a single version of a 3D toolpath. Multiple cutters as well as roughing and finishing passes are simply out of the question. Thanks for the offer to run a part file through Fusion, but that presents another problem; my drawings are all in 2D.

It's not the sophistication of the machine and software that matters, much depends on the man behind the machine. Even a basic machine and basic software can produce good results

Mike
Title: Re: Bristol Mercury revisited
Post by: mike mott on November 14, 2019, 02:58:42 PM
Quote
Even a basic machine and basic software can produce good results

Mike, Thanks for your answer regarding your tooling and I have to agree with your last comment. that said it can be very challenging.

Mike
Title: Re: Bristol Mercury revisited
Post by: Jasonb on November 14, 2019, 04:20:35 PM
Mike just out of interest I sketched up a similar looking par, actually ended up a bit bigger needing a block 91mm x 80mm so actual cut time will be less on the right size part.

Took my less than 15mins to do the CAM and would be a lot less if I really knew what I was doing.

6mm plain cutter to do an adaptive roughing cut in 6mm deep steps max 1mm DOC, then same cutter to finish ends of the three flanges.

Change to 4mm x 1R to do a 3D contour and two little ops to tidy up the bosses and top of the arcs.

With fairly conservative feeds I get 3.34 run time so under 3hrs for the smaller part plus a bit for the holes. looking at the figures there is no material more than 0.05mm above finish profile with the 1mm radius and the small steps I used so minimal file work, a larger stepover would speed things up but need a bit more hand work. I also opted to turn all the waste to swarf, could have left lumps in the coners to save time but don't like the idea of them getting hit by the cutter when they come loose

Blue is the raw material, green is the finish surface.

https://www.youtube.com/watch?v=_WLXVA2JzBM

Photo shows in blue anything at 0.05mm
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 14, 2019, 05:39:06 PM
Jason,

That's a mighty impressive demonstration of the power of Fusion 360.

I think I need to reassess my ideas about the costs of ownership. It could transform the way I make things

Mike
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 14, 2019, 07:53:32 PM
Thanks to Jason's input, we now know that with AutoCAD Fusion 360, JasonB could have done the job twice as well, in half the time. Unfortunately, I do not have Fusion 360.

So let's return to the plot.

While the Jig plate was still mounted on the mill, I machined the three 0.125" wide slots for the pitch control arms. I did not realise at the time, just how essential they would be for chip removal during the later stages.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070654.JPG)


I mounted the Hub Barrel vertically against an angle block. The central propeller blade hole was bored to a diameter of 1 inch using a standard end mill. The bottom of the hole is level with the bottom of the control arm slot. The chips were easily removed from the bore with jet of low pressure air. As you can see it resulted in chips flying everywhere.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070656.JPG)


The interior of the 1 inch bore needed to be opened out to a diameter of 1.5 inches, thereby forming a flange at the top of the bore. The only suitable cutter I had available, was a 1 inch diameter woodruff cutter, which was 3/8 " wide. I would have preferred a narrower cutter as 3/8" presents rather a wide face. The 1 inch diameter woodruff cutter totally filled the 1 inch bore, leaving little or no space for the chips. Chip management suddenly became a serious issue for this stage. I arranged for a jet of air to continuously blow out  the chips as they formed, which resulted in another snowstorm of chips and a spontaneous outbreak of aluminium dandruff. The inside diameter of 1.5 inches was machined in concentric stages from the flange at the top to the bottom of the control arm slot. The slot suddenly became a significant chip clearing path. I directed the air blast into the slot and the chips blew out of the top of the bore.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070657.JPG)


Here you can see the shape of the three bores and the top flange which resists the centrifugal force of the three propeller blades. Also shown is the central splined drive, which will be described in the next instalment.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070677.JPG)


Some work done to improve the appearance of the outside surfaces. Not too shabby from twenty year old CAM software.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070660.JPG)

There's more to follow, so stay tuned.

Mike




Title: Re: Bristol Mercury revisited
Post by: crueby on November 14, 2019, 08:08:54 PM
Very impressive parts!
 :popcorn:
Title: Re: Bristol Mercury revisited
Post by: john mills on November 14, 2019, 08:12:22 PM
I don't think there is much wrong with th 2.5 d simple programs it is surprising what you can do with that
the cost and more the time taken to be able to use the more complex programs can not be justified.I only had a 2.5 d program at the last full time job .before that most of my programming over 15years was done with a pencil and calculator .The smaller computers were not good enough to run cad cam .
Title: Re: Bristol Mercury revisited
Post by: mike mott on November 15, 2019, 06:13:51 AM
Now If I were 21 instead of the added 50 years I think I would invest in some CNC stuff, but hand spinning dials will have to do this time around. Lovely job on the housing Mike.

Mike
Title: Re: Bristol Mercury revisited
Post by: Craig DeShong on November 15, 2019, 02:00:32 PM
Hi Mike.  Beautiful job on the propeller hub. 

You do fantastic work with what you have though and there is no reason for you to upgrade other than convenience that I can see.  Thanks for posting your projects, I find them an inspiration.
Title: Re: Bristol Mercury revisited
Post by: Roger B on November 15, 2019, 05:34:13 PM
Splendid  :praise2:  :praise2: I'm still following along (and still prevaricating about CNC)  :wine1:
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 15, 2019, 09:32:18 PM
Thanks for all of your words of encouragement.

I have put the Hub Barrel temporarily to one side, to get on with the rest of the De Havilland variable pitch propeller hub. I will complete the surface finishing during the final assembly stage.

The next part to be made is the tapered spline drive. I made a similar tapered spline hub for the Bristol Jupiter, just a few months ago See reply #310 part way down this page       http://www.modelenginemaker.com/index.php/topic,7559.300.html. By comparison with the Mercury's tapered splines, the Jupiter was easy.

The Mercury propeller shaft has 24 'V' shaped ( 20 degree included angle) tapered splines. The additional requirement for the 'V' shaped slots moved the challenge up one more notch. I was unable find a keyway broach capable of cutting a 20 degree 'V' shaped slot, so I was unable use the same method as before.  Instead, of the keyway broach, I could make a single point form tool to the required shape. The single point cutter could  be held in a simple boring bar with the cutting edge pointing downwards. All I needed to do now was to find some way of moving the single point form tool up and down at the required slope angle and repeat that move 24 times. Clearly, I needed to devise a different method to the fly press and indexing plate used on the Jupiter's splined hub.

A little ingenuity was obviously called for, How could I find a way to do this with the equipment I have available?  :noidea: :noidea:

Large industrial splines and internal gears are often made with gear planer/ shaper machines. So, could I devise a way of using the vertical axis of the CNC mill to move the cutting tool up and down at the required taper angle and so act like a gear planer/ shaper  The stepper motors on the vertical axis were be able to exert a force in excess of 25 Kgf, which should be enough if I cut the 'V' shaped spines in small depth increments. Also my 4th axis rotary table could be used to index the hub 24 times. All I need now was to devise some way of locking the spindle and holding the single point form tool in a suitable fixed position?

It may look somewhat crude but this is what I came up with. I found and ER24 closing nut which was drilled for a 6mm tommy bar and clamped a bent tommy bar to the mill's headstock. The spindle was now rigidly held in one position.

                              Note to self..... Do NOT switch on spindle motor or use an M3 command.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070665.JPG)


I wrote a short looping program which moved the Z axis downward at the required angle to cut the tapered spline, then retracted the tool before indexed the rotary table through 1/24th of a turn. The program looped and repeated until all 24 splines were cut. Then I advanced the depth of cut by a few thou by moving the rotary table sideways (X axis) and repeated the looped program until the required tapered spline depth was achieved.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070668.JPG)


Here you can see the complete setup. The cutter in the locked spindle is moved up and down in the Z axis. The depth of cut is increased by moving the X axis and the whole tapered spline hub is indexed by the A axis...........Simples.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070670.JPG)


An hour later, you can see the finished tapered spline in the hub, which perfectly matches the tapered spline on the propeller shaft

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070669.JPG)
(https://lister-engine.com/coppermine/albums/userpics/10013/P1070672.JPG)


After that it was a simple turning job on the lathe to finish the outside of the splined hub.

You will see I am using a 2mm wide round nosed parting tool to profile the the rear part of the hub. These parting tools will happily cut sideways as well a plunge, provided you keep the depth of cut small.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070674.JPG)
(https://lister-engine.com/coppermine/albums/userpics/10013/P1070673.JPG)


Finally, a family shot of the Hub Barrel and splined drive

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070675.JPG)


Stay tuned

Mike
Title: Re: Bristol Mercury revisited
Post by: Johnmcc69 on November 15, 2019, 10:32:35 PM
 :ThumbsUp:
 Beautiful parts Mike! Nice setup for cutting the splines.
 Will really enjoy watching all of this come together.
 :popcorn:
 John
Title: Re: Bristol Mercury revisited
Post by: Art K on November 16, 2019, 03:09:14 AM
Mike,
That's some seriously impressive looking parts & setups. I hope I am half as creative if I ever need to make something like this. :ThumbsUp: :popcorn:
Art
Title: Re: Bristol Mercury revisited
Post by: Jasonb on November 16, 2019, 07:12:51 AM
That's a lot easier than pulling on the quill handle like I did for the Robinsons internal gear ;)
Title: Re: Bristol Mercury revisited
Post by: mike mott on November 16, 2019, 07:19:32 AM
You make it all look so simple and easy, But I know that it is not. lovely work on the spline.

Mike
Title: Re: Bristol Mercury revisited
Post by: Steamer5 on November 16, 2019, 08:44:12 AM
Hi Mike,
 That’s gob smacking work !
Thanks for bringing us along.

Cheers Kerrin
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 16, 2019, 05:10:28 PM
Thanks to everyone for calling in. I would not want to misuse the mill, in that way, very often. However it did prove to be an efficient way to cut the tapered splines.

These two Illustrations came from an old 1935 copy of Flight magazine. They show clearly what I am intentending to do. The first is an advertisement for the 'new' Mk VIII version of the Mercury engine. This 'display' engine has stub blades fitted to the De Havilland variable pitch prop. Neat, compact and transportable.

(https://lister-engine.com/coppermine/albums/userpics/10013/Im19371105ACar-Bristol.jpg)


The next illustration shows the true size of the three bladed all metal propeller. It was 12 foot in diameter, so they must have chosen the smallest guy in the hanger ( or a cardboard cutout)  to pose with it. Even at 1/4 scale, it will still be quite large, 36" diameter, not a convenient item to transport or to display at shows. The stub blades would be much more convenient for shows.

(https://lister-engine.com/coppermine/albums/userpics/10013/DeHavilland_VP_Prop-1012.jpg)


The large blades will be necessary when running the engine, so I have been considering how to make them. The originals were forged aluminium, not a convenient process for the home workshop. Many modern microlight aircraft and larger flying models currently use carbon fibre blades. Some are hollow and some are foam cored. I have found some videos on You--tube showing various construction methods and process. I would need to carve a single master blade, from which to take two fibreglass half moulds. The carbon fibre cloth is cut to shape and laid up, with epoxy resin, in each mould half. microballoon filled resin is used to fill the leading/ trailing edge joint line when the two halves are closed. The epoxy resin is allowed to cure at room temperature overnight, I am surprised at this as I rather expected vacuum, vacuum bags and heat to be used.

Have any of our members experimented with making carbon fibre propeller blades? Is it really a practical proposition for the home workshop? If so, what was your experience and what process did you use.

Mike
Title: Re: Bristol Mercury revisited
Post by: ddmckee54 on November 18, 2019, 09:49:06 PM
Is this a static display, or a running engine? For a public display running engine the quick answer will probably be "Don't try it, too much liability."

You might want to ask that same question at RCGroups.com (http://RCGroups.com).  Tell them what you're building, show them what you've done, whether it's for a static display or a running engine,  and you'll probably get a lot of helpful advice.

Don
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 18, 2019, 10:47:43 PM
Thanks Don,

Sounds like good advice. The You-tube videos I saw were from big scale R/C aircraft. I will contact that group directly, as you advise. I have discovered that Bolly Props, in Australia, made the blades for Bob Roache's Pratt and Whitney Wasp radial engine. Unfortunately those blades are 1/6 scale while my Bristol Mercury is 1/4 scale..

All engine running display in the UK are now done within a 8 foot high wire cage, known as the gorilla cage.

The propeller blades are still way in the future. So, here is some present day progress on the De Havilland variable pitch prop hub.

The pitch control arms were milled from hard 3mm brass plate, for wear considerations. I started by coordinate drilling all (7) the bolt holes and then used some of these to bolt the stock onto a sacrificial plate. The milling was straight forward outline profiling.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070681.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070683.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070685.JPG)


The centrifugal bob weights were machined out of steel. The round steel stock was conveniently held in the three jaw chuck of the rotary table, which did not move during this operation.

You will notice both the control arms and the bob weights have a semicircular track for the 3/8" ball race used to change the blades pitch angle. I machined the track with 2 thou. clearance to allow the ball race to slide freely in the semicircular track

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070687.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070692.JPG)


Here is a family photo of all three control arms and centrifugal bob weights. There was only enough room for three steel countersink M2.5 screws to hold the bob weights in place

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070693.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070694.JPG)


As ever:  Stay tuned

Mike





Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on November 19, 2019, 12:00:12 PM
Nice parts so far Mike - both the Hub and this last batch  :cheers:
Title: Re: Bristol Mercury revisited
Post by: mike mott on November 19, 2019, 02:20:28 PM
Very nice work Mike, I can see the value of CNC with these parts.

Mike
Title: Re: Bristol Mercury revisited
Post by: kvom on November 19, 2019, 03:35:08 PM
Using a mill's Z axis for broaching or cutting splines is in no was a mis-use.  The Z axis is in almost every case more rigid and stouter than the X or Y axis.  Even a mini-mill could cut those splines in steel with a sharp cutter and appropriate DOC.

It was nice that you had the mating part available to test the fit each time around.
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 19, 2019, 09:38:53 PM
Per, Mike and kvom,

Thanks for calling in.

Per, Mike, Yes the CNC does allow you to easily make more complex shapes than with a manual machine. I acquired my Austrian Emco machines about 20 to 25 years ago. They were first generation CNC machines and rather crude to operate. They were previously the property of Her Majesty's Prison Service at Parkhurst Prison on the Isle of Wight; home of some real 'bad' boys. I updated the machines with modern (Chinese) electronics and stepper motors. The biggest change came when I converted to the LinuxCNC control system. LinuxCNC is very reliable software and completely transformed the machines

kvom, I only say misused as the spindle and bearings were designed for rotary cutting forces, rather than static loads As you say the Z axis is strong and robust and the cutting forces with every I thou increase in DOC were small. I may have misused it but I certainly did not abuse it.

I don't think I could have made the female splines fit without the mating part (or setting gauge) being available. The spline taper was 1:11 so just 1 thou. DOC would move the spline 11 thou further up the shaft. When the fit and depth of engagement were just right I did not risk to do a spring pass to clean up.



I am trying to make as much progress as possible, before we go away to Pickering in Yorkshire for a short break.

Here is the Control Piston which lives in the very centre of the propeller hub. The hollow Piston is actually fixed (it also acts as the prop nut). The moving cylinder is external and connects to the Control Arms and Bob Weights.

The 'O' seal groove was conveniently formed with a 2mm parting tool

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070688.JPG)


Boring the hollow piston

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070689.JPG)


Machining the hex socket, used to tighten the Piston and variable pitch propeller/ hub to the engine's propeller shaft. Lots of torque and a long tommy bar required here.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070690.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070696.JPG)


Here the completed parts are loosely assembled, THe VP propeller hub is taking shape and beginning to become recognisable.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070698.JPG)

Stay tuned

Mike



Title: Re: Bristol Mercury revisited
Post by: Dave Otto on November 20, 2019, 01:06:57 AM
Beautiful work Mike, you are making great progress on the prop hub.

Dave
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 20, 2019, 09:10:01 PM
Thanks Dave,

The next major part tobe made was the Control Cylinder which moves back and fore and controls the pitch angle of the blades. I started with a reasonably large  ( 2.5" dia x 2"long) billet of HE 30 (6082) aluminium, and using the big Chipmaster lathe, proceeded to turn most of it into a bucket full of swarf. I am always amazed how they get that much swarf into a small billet, in the first place

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070699.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070703.JPG)


Along the way I turned and bored both ends of the Control Piston leaving a full diameter disc of material in the centre, which will later form the three bearing bosses.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070704.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070705.JPG)


I machined the recess in the middle using a 2mm round nosed parting tool. The round nosed parting tool is a very convenient way to machine both sides and face of a recess and also leave nicely radiused  fillets in both corners. I then screw cut a short tread (26TPI) in the front for the Cylinder Cover Plate.

Actually I got this far twice. :facepalm: :killcomputer:      I destroyed the first attempt by pressing the wrong button at the wrong time. The tool dug in and pulled the work out of the chuck. There was no option but to start again and fill another bucket with swarf.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070706.JPG)


I used a hacksaw to remove a lot of the excess metal from the disc, in order to reduce the amount of machining required. The Control Cylinder was then placed in the 4th axis unit so the three bearing bosses could be machined and accurately indexed.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070707.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070708.JPG)


Here the bearing bosses are being drilled and tapped to receive the the three Bob Weight bearing pins. The ends of the bosses were profiled to shape using a very long and slender 4.0 mm end mill There was far too much overhang but it was necessary to prevent the collet holder from striking the jaws of the 3 jaw chuck. Needs must....

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070709.JPG)


I also needed to make a special double ended spanner/ socket to tighten the Piston (prop nut) and then the Cylinder Cover Plate

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070719.JPG)


Here is the Piston being tightened with the special spanner/ socket

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070720.JPG)


And then the Control Cylinder Cover Plate

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070722.JPG)


Here you can see the loose assemble of the parts made so far. You will have to wait a couple of weeks before I can tackle the three stub propeller blades and finish the assembly.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070723.JPG)


Well you said you liked photos, lots of photos

Stay tuned

Mike
Title: Re: Bristol Mercury revisited
Post by: cnr6400 on November 20, 2019, 09:57:50 PM
Looking great Mike!  :ThumbsUp: :ThumbsUp: :ThumbsUp: :popcorn: :popcorn: :popcorn:
Title: Re: Bristol Mercury revisited
Post by: crueby on November 20, 2019, 09:58:22 PM
Very impressive parts! :popcorn: :popcorn: :popcorn:

Maybe thats why the metal is expensive, its so hard to pack the swarf into a bar? Hmmmm....  :thinking:
Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on November 21, 2019, 11:53:02 AM
Quote
Very impressive parts! :popcorn: :popcorn: :popcorn:

I will have to agree  :praise2: and I do really like the special dual function tool - nice detail + you do not need to look for both :ThumbsUp:
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 21, 2019, 04:54:46 PM
Thanks guys for calling in.

Here is the second Bristol Mercury MK VIII engine with the reduction gearbox and the variable pitch propeller hub loosely reassembled.  The Control Cylinder is in the extended, fine pitch, position

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070730.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/VPprop8.jpg)

I will be able to make a start on the stub blades in a couple of weeks.

MIke
Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on November 21, 2019, 09:14:09 PM
It looks fantastic Mike :cheers: but as you plan to run it from time to time - isn't it "missing" an exhaust collector (not on the poster either) or are you "planning on" getting dosed in different "nasties" ? :old:

I know it will add quite a bit off more work ....
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 21, 2019, 10:54:40 PM
Ha ha, Per wants an Exhaust Collector Ring, just like a real engine. :lolb: :lolb: :lolb:

OK you can have one, provided Santa over in Denmark is taking Christmas orders, If not I don't think it will happen in my lifetime. :old:


I have looked many times at what would be involved and quickly realised it was way beyond my equipment and skills. Bristols sub-contracted the Collector Ring work to a specialist sheet metal company who built many hundreds and thousands for the Mercury and most of the other Bristol radial engines. They used accurate fabrication jigs to keep everything aligned and had lots of practice supplying a very demanding customer.

The Exhaust Collector ring is basically two deeply dished mild steel pressings. The pressings were joined front and rear to form a streamlined donut. Eighteen exhaust flanges were then accurately attached using a huge alignment jig. Mounting brackets and all the furniture for the engine cowlings etc were also added. The full size Collector Rings were mostly riveted with some spot welding in the more accessible places. I would need to reproduce much of that production facility, I may get away with precision TIG welding, but guys who can do that quality of precision welding work are way too expensive.

The ARC company in Duxford supply airworthy Mercury engines to a number of flying vintage aircraft, the Blenheim light bomber, the Gladiator biplane fighter and the Lysander. The supply of Exhaust Collector Rings is a big problem for them. None have been made in the last seventy years and the supply of usable hardware is fast diminishing. All the flying engines have been patched and repaired numerous times and all museum engines have been raided.

In the end, I told myself that most of the model engine would e hidden behind the Exhaust Collector Ring and then tried to forget the idea. Actually there nothing better than a few oil splashes on your teeth, when you are grinning with joy, behind an engine running with open exhaust ports

But if you would like to provide one.......

Cheers

Mike
Title: Re: Bristol Mercury revisited
Post by: petertha on November 22, 2019, 07:26:56 AM
Many modern microlight aircraft and larger flying models currently use carbon fibre blades. Some are hollow and some are foam cored. I have found some videos on You--tube showing various construction methods and process. I would need to carve a single master blade, from which to take two fibreglass half moulds. The carbon fibre cloth is cut to shape and laid up, with epoxy resin, in each mould half. microballoon filled resin is used to fill the leading/ trailing edge joint line when the two halves are closed. The epoxy resin is allowed to cure at room temperature overnight, I am surprised at this as I rather expected vacuum, vacuum bags and heat to be used. Have any of our members experimented with making carbon fibre propeller blades? Is it really a practical proposition for the home workshop? If so, what was your experience and what process did you use.

Hi Mike. You might want to tread a bit careful here because the consequences of failure would be rather nasty. I've molded a few CF props which were modified from existing blades in RC racing & other RC high performance applications. Its pretty finicky to do right even with a lot of composites experience. Mostly we rely on commercial props because they are highly engineered & the work to replicate is substantial. These were typically thin section props, inevitably solid fill CF unidirectional 'tow' in the core. The outer skin may well be CF cloth or more predominant these days, spread tow (the wide check stuff). I'm less up to speed on the bigger props but my hunch is their construction varies by size & application. I've heard many use a composite core like structural foam. I suspect what makes this possible is relatively thicker cross sections working to advantage. The (bending & torsion) stress load is highest near the root & diminishes outward to the tip. A broken ~28" prop I saw at the field had thicker lamination sequence near the hub & then diminishing progressively outward which makes sense, matching stress profile. Your prop might be more in this range but the devil is in the layup details.

I think high quality epoxy laminating resins would be a prerequisite. Heat treating (post curing) is often required to obtain strength. Depending on the resin & application, this can occur after initial cure. I am aware of folks using pre-preg CF which mostly eliminates the liquid resin lay up process. These may or may not use vacuum, but these must be temperature cured for sure. For conventional layup, MGS epoxy resin is very good (now under Hexion mae?). Its a German aircraft resin with different hardners available, but more importantly generally available in modelling quantities. My sources in NAm will not work for you but this company is very reputable & closer to you. https://shop1.r-g.de/en/art/112104

Down near the bottom, some pics of modern CF folder props & cnc made female molds from tooling urethane.
https://www.facebook.com/pg/GMPropellers/photos/?ref=page_internal

Probably not the profile you are after but example of larger diameter 'sport' CF props commercially available. I mention this more as a potential resource, maybe you could mill the molds because you are likely after a specific scale shape & request input (or possibly farm out) as to the specialty layup experience. Most of these 'factories' are really micro production specialty shop hobby enthusiasts that might be able to offer some help especially when they saw the intended application.
http://www.espritmodel.com/pt-propellers-glowgas-carbon-fiber.aspx

I'm not an expert but thought I'd give you an overview. Be careful about what you read on RC forums specific to composite props. I don't mean that in a bad way but just be aware there is a range of knowledge & skill levels, but kind of hard to sort out what is safe & what is an eminent failure waiting to happen. Still admiring your work!
Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on November 22, 2019, 11:41:15 AM
OK - so I hit the Hornets nest ....  :LittleDevil:  and I should have know a few things here - like you would only accept a true model replica of the original exhaust + realizing that it might be so big that it obscured the view of your beautiful engine  :-[ (we can't have that).

I did notice the dual exits on each head, but I have also seen your great uses off jigs - so I figured that you where one of those individual that actually could pull it off ....

And NO - I do not have any connection's with the Man in Red.
Title: Re: Bristol Mercury revisited
Post by: Allen Smithee on November 22, 2019, 01:41:26 PM
I used to make carbon props for my FAI-F3D pylon racers, but these were "solid" - just carbon tows and epoxy in a mould and heat-cured, two blades and around 8" diameter. I made some bigger glass/epoxy ones (up to 14") for static display, and some individual blades intended for a constant-speed prop project that I never finished. These were hollow shells bonded together, but I was never sure about their strength.

I would say that to to it for *running* props you'd need to approach it using vacuum-bagging to consolidate the lay-up, and then post-cure heating to stabilise the resin. Another pretty essential trick is to cut out all the cloth/tow that you will be using and weigh it using an accurate balance. You then use trhis to weigh out the resin you will use. This ensures consistent resin/cloth ratios and also puts you in with at least half a chance of making balancable blades!.

How you intend to make moulds depends on what processes you intend to use. If you want to heat-cure then you must either the same material you make the blades from, or a decent high-temp tooling resin or (if you're a billionaire) a fully-machined and polished steel. Forget aluminium, it expands and warps when you heat it. If you're going to do your initial cure "cold" and then use heat to post-cure (which produces exactly the same result) then you can make much simpler/cheaper molds from basic fibreglass matt and/or car body filler.

Finally - I wouldn't use resin/microballon as a shell-jointing system because it has no strength at all (and is brittle). Better options are milled fibres, glass flocking or foamed resins.

See also my PM

AS
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 22, 2019, 02:36:17 PM
Per, it's not a problem, it's not a hornets nest. I researched the possibilities of making a neat Exhaust Collector Ring some time back and concluded it was not going to happen.

AS, petertha and Don, thank you all for your feedback regarding CF blades, That was exactly the informed feedback I had hoped for. I am always suspicious of You-tube 'How to do it' videos. Too many time wasters, too many willy wavers, providing trivial content. But it was a starting point for my investigations. In professionally made CF blades the careful attention to the layup details is obvious for the correct distribution of the loads and forces. The manufacturers will have developed their process the hard way and understandably are not going to give their technology away.

So, what to do?

I am not wed to the idea of having CF blades. Likewise, I am not wed to having a VP propeller or even a three blade prop for that matter. I was only researching the possibilities. When the time comes to run the engine, it will only be for ground running demonstrations, never for flight. For ground running I only need a suitable load for the engine, one which does not produce too much wind.  The logical and obvious conclusion is to buy and fit a large professionally  made, fixed pitch two or three blade propeller. It does not need to have a 1930's scale appearance, It is there only to provide a load for the engine, not for looks. Most of the time, the big propeller will be removed anyway. A while ago, I found (and since lost) the details of a Czech company who made large model propellers in the region of 36" diameter. I will look again when the time comes.

Thanks again for your valued feedack

MIke
Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on November 22, 2019, 04:09:33 PM
Mike the comment was meant as a joke - just like I expect yours about me making a collector for was  ;)

On a different note - don't you think that there exist clubs for the extremely big model that are flown today ?  Because if so, there should be a chance that one or two of them would know where to buy those blades / a fixed prop in the right dimentions - if the right price is possible.
Title: Re: Bristol Mercury revisited
Post by: Allen Smithee on November 22, 2019, 05:21:38 PM
A while ago, I found (and since lost) the details of a Czech company who made large model propellers in the region of 36" diameter. I will look again when the time comes.

No need to go to the Czech Republic - Punctillo  are a british firm (based in Norfolk) who have been making wooden props for model aircraft, target drones and UAVs for decades. The last time I asked they were more than happy to do non-standard one-offs, so I'd try them first:

http://www.punctiliopropellers.co.uk/punctilio1.htm (http://www.punctiliopropellers.co.uk/punctilio1.htm)

AS
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 22, 2019, 05:23:30 PM
Thanks AS  :ThumbsUp: :ThumbsUp: :ThumbsUp: :ThumbsUp: I will give them a call

MIke
Title: Re: Bristol Mercury revisited
Post by: Allen Smithee on November 22, 2019, 05:41:53 PM
If they can't help then let me know. I have friends in that world - I remember one had a scale 36" 3-blader made to suite a large scale spitfire 1a (the prop was actually used for flight as well).

AS
Title: Re: Bristol Mercury revisited
Post by: ddmckee54 on November 22, 2019, 10:30:55 PM
Since you only want the prop for a load while ground running, why not have 2 props?

One would be your working variable pitch prop used for static display only.  That way there would be no reason to worry about the prop tearing itself apart under load.  You could make the parts in the easiest, or most scale-like, manner and not have to worry about their strength.

For running swap that beauty out with a cut down and rebalanced, but butt-ugly, fixed pitch prop commercial prop.  You only need to move enough air to cool the engine, you're not exactly looking for maximum performance.  You could also swap out your beautiful, but probably fiddly prop nut, with a beefier more utilitarian version, just for ground running the engine.  I've read that that's what is done at most flying scale model competitions.  You swap out that scale prop that you've sweated over for hundreds of hours to get every detail and every scratch and chip in the paint looking JUST right, with a commercial prop that's only going to be a round blur when it's in the air.

You could even build a scale prop cart, to hang the spare prop and extra parts on, while they're awaiting their turn in the spotlight.

Don
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 22, 2019, 11:01:48 PM
Hello Don,
Having listened to your and others advice about the reality of building my own CF blades, I have arrived at more or less the same conclusion. Two props, one to show and one to run.  However, I have decided to give the show VP prop three cut down stub blades, like those used by Bristol's for their display engines and shown in some of my photo attachments.
The reason is simple. A 36 inch three blader is still a big arkward thing, that would need to be transported separately and would also need the engine to be unnesserily high off the bench. I am quite happy with the stand I already have and how it looks.

Thanks for calling in

Mike
Title: Re: Bristol Mercury revisited
Post by: Art K on November 23, 2019, 12:28:22 AM
Mike,
Sorry, I  can give you no help in the prop area cept talking to the big guy upstairs, for all the help that will give you. But as is normal from you some excellent work on the prop hub.
Art
Title: Re: Bristol Mercury revisited
Post by: petertha on November 23, 2019, 03:11:41 AM
A while ago, I found (and since lost) the details of a Czech company who made large model propellers in the region of 36" diameter. I will look again when the time comes.

The link I embedded in my post is for Esprit, a USA dealer, but the do a lot of business with Czech companies. Might be the same as what you found, or might be coincidental. The manufacturer name is PT & sized up to 34x12.
http://www.espritmodel.com/pt-propellers-glowgas-carbon-fiber.aspx

But looks like you can get direct from your side of the pond
https://www.ptmodel.cz/en/glow-gas-propellers.html

The other avenue I wouldn't dismiss given your talents is making a laminated wood prop. If they are strong enough for FS engines, they should be fine for a scale running model. For the same effort it takes to make a positive for a mold, you might just use it as the prop itself. Its not like you are after optimal thrust at altitude. Its basically must provide a suitable load, looks right according the original engine application & make wind. You could finish it with resin & do a nice brushed aluminum finish with auto paint & nobody would be the wiser more that 12" away. Some of the scale RC guys 'paint up' commercial props in that manner if the RC shape doesn't look too far out of place.
Title: Re: Bristol Mercury revisited
Post by: Allen Smithee on November 23, 2019, 08:38:56 AM
Just to clarify - ordinary model shops carry wooden and carbon props up to at least 32" dia (including a limited range of 3-bladers). If that's big enough for your needs then you can look to the usual sources - Sussex Model Centre, Als Hobbies, Kings Lynn Model Centre etc etc and get them off the shelf.

AS
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 23, 2019, 10:42:27 AM
Thanks, I will follow this up later

Mike
Title: Re: Bristol Mercury revisited
Post by: Roger B on November 24, 2019, 08:52:53 AM
That's an interesting variable pitch hub  :ThumbsUp:  :ThumbsUp: The forces on the blade roots must be quite high compared to a conventional propeller where the blades can get thicker close to the root  :thinking:
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 24, 2019, 11:14:08 AM
You may be correct about high centrifugal forces at the hub. The three blade were forged light alloy, it may have had a magnesium content as most surviving blades suffer from extreme corrosion. There was a roller thrust bearing at each blade root

Mike?
Title: Re: Bristol Mercury revisited
Post by: Art K on November 24, 2019, 09:31:21 PM
Mike,
The thrust bearing at the base of the prop makes a lot of sense due to centrifical loading. I can imagine that without it at speed it would be impossible to rotate.
Art
Title: Re: Bristol Mercury revisited
Post by: Allen Smithee on November 25, 2019, 07:44:17 AM
I would think a pair of opposed tapered roller bearings, or perhaps a plain bearing at the "blade" end and a tapered roller bearing at the inner end would be worth considering for the combination of axial and lateral loads. One of the reasons my constant speed prop project got parked was a lack of confidence in my calculations for these stresses.

AS
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 25, 2019, 10:44:15 AM
This discussion could become interesting and perhaps controversial
If you do a full anylasis of the forces acting on the root of a folding/variable pitch prop blade you find some surprising results. The centrifugal force dominate the hydro/ aero dynamic drag and lift forces to such an extent that you can virtually ignore all forces except the centrifugal force.

This is counter intuitive but the number don't lie, you have to trust them.

As an example, you only need to look at the VP tail rotor (and some main rotors) of a model helecopter. The blades are held by a simple pin joint and are free the Flop about in a clock/anti clock direction. When they spin up the centrifugal forces swing the blades out to their correct operating position. The drag forces do not fold the blades flat.

While I was working, we designed a small folding prop blade, tube launched wire guided underwater device (not quite a torpedo) . The prop blade folded clockwise within the body diameter and deployed, into the direction of rotation when the propulsion motor spin up.

The hub of the De Havilland VP hub only has a single, flat roller thrust bearing, which is preloaded to prevent the blades flopping about when the engine is stopped. There are no plain bearings to resist bending forces. Actually the thrust bearings are basically static bearings, they only rotate the blades through 20 degrees twice per flight.

I am away from home, this week, otherwise I would post the works drawings of the hub.

I know it's counter intuitive but analysis does show the centrifugal force dominate the bending forces allowing a single bearing blade root

Mike
Title: Re: Bristol Mercury revisited
Post by: Allen Smithee on November 25, 2019, 01:36:58 PM
I'm not *that* surprised, but I do wonder if it depends on what the aeroplane is doing. The aeroplane my CS prop was intended for was likely to spend a lot of time doing flick manoeuvres, lomcevaks etc and these rapid gyrations impart significant gyroscopic stresses. I note that "agile" helicopters tend to have rather more lateral/vertical blade location in the main blade mounts, and the so-called "3d" RC helicopters have stabilised to having two axial ballraces and a thrust race holding the blade pintel shafts (or an outer ball race and an inner angular-contact bearing in one case).

But none of that is relevant to a prop for an engine that will only ever be bench run. In that case I guess you're really just after blade containment, so a hub with something like a tapered roller or thrust race to take the centrifugal loads and a simple ballracem needle roller or plain bush outboard of that as a blade steady should be enough. You could then ensure the containment of composite blades by just having a spar made from carbo tows which start at the blade tip, pass down the blade and around retaining features in the pintel shaft and then back to the tip. This is essentiall what we did with the "solid" carbon F3D props - half the toes went tip-to-tip, striaght  past the hub. the other half went from a tip, around central pin (which formed the mounting hole) and back to the same tip, alternating each blade for balance. These props would break on contact with the ground (or in mid-airs) but never shed a blade due to revs (over 31k in some cases).

AS
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 25, 2019, 02:52:58 PM
The design point I described relates to relatively steady state conditions with sufficient prop RPM's to generate the large centrifugal forces. Your extreme manoeuvres and wide rev range will not doubt create a different set of load conditions to those experience by the De Havilland VP prop.

Mike
Title: Re: Bristol Mercury revisited
Post by: Vixen on December 05, 2019, 04:22:23 PM
Just returned from a very wet week in North Yorkshire to a cold and frosty south of England. However some progress has been made on the VP propeller hub.

The three stub blades were straightforward turning on the lathe, followed by drilling and tapping the M4 screw threads in the base. The full size propeller hub has three, two piece, loose roller ball thrust races, which must have been a real pain to assemble. For simplicity, I substituted a one piece brass thrust ring and a PTFE thrust bearing. Both items were milled from flat stock.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070752.JPG)


Here we can see the three stub blades resting in the Hub Barrel halves

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070751.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070750.JPG)


This is the Hub Barrel loosely assembled. Amazingly the three stub blades rotate freely.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070755.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070754.JPG)


The next job is to connect up the Control Cylinder to roller bearings in the Control Arms and do whatever is necessary to get full and free propeller pitch movement through the entire 20 degree pitch range.

Mike
Title: Re: Bristol Mercury revisited
Post by: scc on December 05, 2019, 09:05:36 PM
BEAUTIFUL      :popcorn: :popcorn:          Terry
Title: Re: Bristol Mercury revisited
Post by: Vixen on December 06, 2019, 02:39:32 PM
Thanks Terry.

The whole De Havilland variable pitch propeller hub assembly went together with very little trouble. All that was required was a few strokes with a file to enable the hub to move to the limits of travel. Here you can see it in the course pitch position
I am now just waiting for the castile nuts and bolts, which clamp the Hub Barrel halves together, to be delivered

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070759.JPG)


There is a 85 year gap between these next two photos. Which reminds me that I have still to make the two crankcase breather tubes.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070757.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/Im19371105ACar-Bristol.jpg)

Well, I'm close to crossing another part off that endless list.

That's it for now

Mike

(http://)
Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on December 06, 2019, 08:12:45 PM
Great work Mike  :cheers:

I must admit that in my mind the stub where a bit longer than they turned out to be - but the last picture really drives the point home to me. The biggest difference (besides scale) is the quality of the old print and the new + now you mentioned it the missing breather tubes.
Title: Re: Bristol Mercury revisited
Post by: Vixen on December 12, 2019, 06:57:53 PM
It's gone very quiet of the Forum lately, probably due to the winter weather. I thought it needed someone to post something for the petrol heads.

As Per pointed out, the crankcase breather pipes were missing from the previous photo. So they became the next bits to make.
The breather pipes were made form 12mm diameter thin wall tube. The upper flange was made on the lathe and then transferred to he mill, to profile the end flange and drill the four mounting holes. Forgot the photos.

The lower brackets were originally castings but, for the model, they would have to be carved out of the solid. Their awkward shape would provide an interesting exercise in work holding. The machining required the profiling to shape of three faces, the base and both sides. This would require square stock, sufficiently long for most of the machining to take place on the overhanging section beside the machine vice.

The first opp was to profile the bottom face of the lower mounting bracket

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070761.JPG)


The block was then rotated to allow the first side to be profiled and the recess hollowed out with a 2.0mm diameter end mill.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070762.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070765.JPG)


A confidence check to ensure the breather pipe would fit the bracket

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070767.JPG)


The block was flipped over to the opposite side of the machine vice for the other side profile and recess to be machined. I touched off the far end of the bracket and the lower face, to redefine my datum.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070772.JPG)


Here is the first bracket being parted off from the stock material.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070773.JPG)


The end result look like a pair of miniature tooth brush holders. The brackets are still in the raw, as machined, state and will need some hand work with needle files to round the edges and give them  the required 'casting' look. The mounting holes are yet to be drilled to match the fixings in the engines crankcase.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070774.JPG)


The final photo shows the two crankcase breather pipes loosely assembled to the front of the engine. I don't think they are a very pretty design, more like two rain water down pipes, almost an afterthought. However they are completely true to the original.

Another small detail crossed off the seemingly endless list.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070779.JPG)


This winter is already dragging on, and it's still only early December

Mike

Title: Re: Bristol Mercury revisited
Post by: mike mott on December 12, 2019, 07:10:52 PM
Mike the more I watch the intricate shapes that you are able to produce the more I learn about sequencing the work of making these sorts of parts.

Mike 
Title: Re: Bristol Mercury revisited
Post by: scc on December 12, 2019, 07:12:53 PM
I love watching parts like this carved from solid lumps :ThumbsUp:  Inspiring        Terry
Title: Re: Bristol Mercury revisited
Post by: Dave Otto on December 13, 2019, 12:38:28 AM
Very nice as usual Mike!

Dave
Title: Re: Bristol Mercury revisited
Post by: 90LX_Notch on December 13, 2019, 01:37:58 AM
Outstanding work Mike.  I always look forward to your updates.

-Bob
Title: Re: Bristol Mercury revisited
Post by: Jasonb on December 13, 2019, 07:13:07 AM
Your getting there Mike, would the bracket have had a separate split cap on the original as the shape looks like it should clamp around the tube with a couple of bolts to close it up?

J

PS As I had another runner at the weekend I'll start a new IC build thread soon so it won't be so quiet for you.
Title: Re: Bristol Mercury revisited
Post by: Vixen on December 13, 2019, 12:12:12 PM
Thanks everybody for calling in,

Carving an engine part from a solid billet is fun and a challenge. You need to think the whole process through from beginning to end, before you start cutting metal. It is all too easy to machine away the datum or the means of holding the work for the next operation. The last thing you want is to find a holding clamp just where you wish to place the cutter.

Yes, the bottom bracket does have a split cap. However it is far more convenient to machine it as one piece and seperate the cap with a fine slitting saw after all the holes are drilled and tapped and the outside filled to shape.

J   Looking forward to your next build thread

Mike
Title: Re: Bristol Mercury revisited
Post by: Art K on December 14, 2019, 01:40:25 AM
Mike,
As usual you managed to make a very elegant part. I always look forward to see what you're up to.
Art
Title: Re: Bristol Mercury revisited
Post by: Roger B on December 14, 2019, 03:32:51 PM
Excellent metal sculpting as ever  :praise2:  :praise2:  :wine1:
Title: Re: Bristol Mercury revisited
Post by: Vixen on December 15, 2019, 05:05:57 PM
Art Roger  :ThumbsUp: :ThumbsUp:

Just a quick update. I cleaned up the machined brackets with a file and abrasive paper to make them look more like castings, including the draft angle. Then I used a 16 thou (the thinnest one in my box) to part off the caps. Finally a quick finish with a disc of Scotchbrite in the Dremmel, to produce a nice even matt finish.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070780.JPG)


The three little scoops are to catch the oil thrown around in the reduction gearbox in order to redistribute it in the cam gears. Nothing is wasted.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070781.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070782.JPG)

That's it for a short while.

Mike
Title: Re: Bristol Mercury revisited
Post by: Jasonb on December 15, 2019, 05:15:07 PM
They look good, Being clamps you actually want a gap between the two halves so they pull up tight unlike say an eccentric strap where you don't want a gap.
Title: Re: Bristol Mercury revisited
Post by: crueby on December 15, 2019, 05:30:34 PM
Love the finish! How did you hold the scotchbrite in the dremel?
Title: Re: Bristol Mercury revisited
Post by: Vixen on December 15, 2019, 05:52:37 PM
Hello Chris,

I cut the discs of Scotchbrite by hammering a sharpened length of steel tube into the end grain of a wooden block. I find the red/brown grade works best.

The discs are mounted in the same way as a cut off disc. The screws are M1.5 if you need a longer replacement.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070783.JPG)


I usually mount two discs at a time, but they don't last long if you are against a sharp edge. Bits fly everywhere, so wear goggles to protect the plastic lenses of your glasses.

Ohh, keep the Dremmel speed as low as possible.

Mike

Title: Re: Bristol Mercury revisited
Post by: crueby on December 15, 2019, 06:41:26 PM
Great tip mike! Good time to use the face shield and apron, sounds like.
Title: Re: Bristol Mercury revisited
Post by: Vixen on January 04, 2020, 03:12:13 PM
I thought some of you may be interested in the bevel reduction gearbox which fits between the engine's crankcase  and the variable pitch propeller. It drives the propeller shaft at half engine speed.

You can see the reduction gearbox is very neat and compact. It consists of two large bevel gears and three smaller ones which rotate the central propeller shaft. The large bevel gear at the front is static and is bolted rigidly to the bell housing surrounding the gearbox. The large bevel gear at the rear is driven by the engines crankshaft via a large diameter splined coupling. The three smaller bevel gears are mounted on stub shafts which are part of the propeller shaft. The propeller shaft turns at half engine speed.

(https://lister-engine.com/coppermine/albums/userpics/10013/DSCF4668.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/DSCF4672.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/DSCF4673.JPG)


The central propeller shaft was machined from a length of 3.125" diameter Mild steel (EN8) The shaft is hollow and was made from two pieces, the main shaft which carries the small bevel spider and a smaller tail shaft. The first operation was to turn all the features on the front of the shaft and also the tail shaft. The embrio propeller shaft was then rotated in the chuck to bore the central cavity and turn the rear details. The tailshaft was then loctited in place and the tail shaft outer diameter turned to run truely concentrically with the main propeller shaft

(https://lister-engine.com/coppermine/albums/userpics/10013/Image0001.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/Image0003.JPG)

The 40 TPI bearing retainer screw threads were machined on the lathe before The propeller shaft assembly was transferred to the milling machine to machine the three stub shafts which carry the three smaller bevel gears.

(https://lister-engine.com/coppermine/albums/userpics/10013/Image0004~0.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/Image0005.JPG)


The propeller shaft was then transferred to the dividing head for the tapered splines to be machined. The rear of the shaft is being supported by a bearing block. I made the special spline cutter (similar to a gear cutter) from hardened silver steel. The splines were machined in a similar manner to a spur gear but with the added complication of adding the taper half angle.

(https://lister-engine.com/coppermine/albums/userpics/10013/Image0007~0.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/Image0008~0.JPG)


The bevel gears were based on commercially available stock gears made by HPC. They were generated by HPC on a gear shaper so each gear tooth had the correct taper and cone angle. The stock gears were all modified in the lathe as required for their individual  bearings and mounting requirements

(https://lister-engine.com/coppermine/albums/userpics/10013/Image0010.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/Image0011.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/Image0012.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/Image0013.JPG)


 There are thrust bearings outboard of the bronze bearings on the three smaller bevel gears and two large diameter ball races to support the propeller shaft. The whole reduction gearbox was carefully assembled and shimmed to achieve the correct meshing of the bevel gears.

The whole reduction gearbox runs very smoothly and effortlessly, once I had learned how to hold the gearbox, to avoid nipping my fingers in the gears. The straight cut bevel gears produce a slight tinkling sound when rotated dry. The outer bell housing forms an oil bath for the gears as well as transferring the propellers thrust and torque forces back into the engines crankcase.

Stay tuned

Mike

Title: Re: Bristol Mercury revisited
Post by: propforward on January 04, 2020, 03:19:49 PM
That is lovely work Mike - very nicely done.  :NotWorthy:
Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on January 04, 2020, 06:43:06 PM
Amazing result Mike  :cheers:

Am I right in assuming that you milled the "The propeller shaft assembly" i two different setups before doing the splines - one where the shaft was parallel to the mill bit (probably mounted in the divider) - and another with the shaft mounted somewhat like you show in the picture where you cut the spines - so you could mill the tree stubs for the small bevel gears ...?

Per
Title: Re: Bristol Mercury revisited
Post by: Vixen on January 04, 2020, 07:02:58 PM
Hello Per,

The milling of the propshaft used several set ups. A lot of my photos were lost in a PC crash a while ago, so I cannot show them to you.

I started with the propshaft mounted vertically, so that the bulk of the big ring could be machined away and to profile the shape next to the hub. This left three square pegs sticking out. The propshaft was then transferred to the horizontal position, in the dividing head, to machine the three stub shafts from square to round. I used a boring head, with the cutter facing inwards, to bore/ turn the stub shafts to size. The spines were cut with the shaft parallel to the X axis. The half angle was machined by a coordinated move in the X,Y axes.

Mike
Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on January 05, 2020, 07:40:33 PM
Thank you Mike - that more or less confirmed my suspicion about how you did it - though I didn't thinK much about the reverse drilling head, but it certainly makes the round surface perfect for use as an axle :cheers:

Shame about the PC accident - they have only happened a few time for me since late 1980's as hardware faults - and a few more from "Error 40" (that should probably be "Error 25" in the Non-Metric world)  :-[
Title: Re: Bristol Mercury revisited
Post by: Vixen on January 06, 2020, 12:26:33 AM
Hello Per,

You can get lots of satisfaction from devising a way to machine a component using only what you have available in the shop. The alternative is to buy more and more machines and tooling which may never be used again. I prefer to use some nginuity whenever I can, instead of the cheque book.

You only get caught once with a computer crash. After that you learn the lesson about backing up important programs and data. In a way our MEM forum is also a great backup of all our images and a record of all our projects. it's good to be able to look back to find out "how did I do that" and hopefully the information can help others facing similar challenges.

Mike
Title: Re: Bristol Mercury revisited
Post by: steamer on January 06, 2020, 12:48:35 AM
That's looking sweet Mike!...

Dave
Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on January 06, 2020, 10:56:53 AM
We used to say that the error was 40cm / 25" from the keyboard, when I worked in IT ....
Title: Re: Bristol Mercury revisited
Post by: Jo on January 06, 2020, 05:05:01 PM
Best kept at arm's length then  ;)


I can never understand why when three generations have been brought up in the UK on metric measurements people are determined to still use legacy measurements that the kids don't understand :noidea:

Jo
Title: Re: Bristol Mercury revisited
Post by: Roger B on January 06, 2020, 05:35:54 PM
I think most kids understand arms length  :stir: my wife's Scottish Gran used to always tell her to keep a Herrings length away from boys/men  :)
Title: Re: Bristol Mercury revisited
Post by: Vixen on January 06, 2020, 05:40:58 PM
Quote
I can never understand why when three generations have been brought up in the UK on metric measurements people are determined to still use legacy measurements that the kids don't understand :noidea:
Jo

Jo, I must belong to a previous generation to the three you refer to. I was brought up using inches, I learned machining on old inch machines. I then spent the second half of my working life designing underwater vehicles using the metric system. So, I am totally happy with working in both measurement systems and swap between the two on a daily basis. However, I prefer to design all my engines in metric but still do all the machining in inches. With CNC measurements are just numbers. Besides, many of our MEM members are from parts of the world where inch measurements are the norm while other countries use metric. We need to be prepared to talk and think in both measurement systems. And also be prepared to keep a Herrings length away from boys and men like Roger said.

So you will understand when I saw Per referring to Error 40 and Error 25, I immediately thought 40 thou" equals 1mm (39.37 to be precise) and 25.4 mm equals 1 inch

I like the look of your new 3D printer.

Mike
Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on January 06, 2020, 10:35:36 PM
I admit that I already used " " as quotes - so it did not feel right to have " next to the last for indicating inches, and that kind of let Mike down the wrong path ....   :-[
Title: Re: Bristol Mercury revisited
Post by: Art K on January 07, 2020, 02:37:50 AM
Mike,
Using and interchanging inch and metric is fine as long as it's not a Mars probe that you forget to convert and cause it to crash into the red planet. :lolb:
Art
Title: Re: Bristol Mercury revisited
Post by: Jasonb on January 07, 2020, 08:04:29 AM
I think most girls will understand imperial when it comes to bust size and as for the lads :-X

The bigger problem is 40cm/25" when 40cm is nearer to 16" which is a rather short arm and those pesky cm that the Europeans like to use rather than mm. :LittleDevil:
Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on January 07, 2020, 11:35:26 AM
Ups - you're right Jason i even got the conversion wrong  :facepalm:
Title: Re: Bristol Mercury revisited
Post by: Vixen on January 07, 2020, 12:18:53 PM
Ha Ha !!!

Watch out Mars, Per may be on a collision course.   :lolb: :lolb: :lolb:

Mike
Title: Re: Bristol Mercury revisited
Post by: Art K on January 07, 2020, 01:25:02 PM
Ha,  :lolb:
Art
Title: Re: Bristol Mercury revisited
Post by: crueby on January 07, 2020, 03:54:53 PM
Side of a mountain on Mars, here they come....  :Jester:
Title: Re: Bristol Mercury revisited
Post by: kvom on January 07, 2020, 03:57:50 PM
Like the Far Side cartoon where one pilot asks another, "What's a mountain goat doing up here in the clouds?"
Title: Re: Bristol Mercury revisited
Post by: crueby on January 07, 2020, 03:59:49 PM
Like the Far Side cartoon where one pilot asks another, "What's a mountain goat doing up here in the clouds?"
Title: Re: Bristol Mercury revisited
Post by: Art K on January 07, 2020, 08:45:01 PM
Ouch!
Art
Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on January 07, 2020, 09:35:51 PM
I haven't been strapped onto the rocket yet .... as far as I know ....

Oh and I'm sure I could identify Olympus Mons from low orbit if it came down to that .... don't know if that would be too late to avoid crashing into the biggest volcano in this Solar system though  :-\
Title: Re: Bristol Mercury revisited
Post by: Vixen on January 17, 2020, 09:40:46 PM
I am pleased Per took all that leg pulling with a good heart.

I have been making the final bits for the Bristol Mercury crankshaft assembly. Small items like woodruff keys and other fidelity small details.

Here are all the components for the crankshaft layed out for a family photo.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070912.JPG)

From left to right are the reduction gearbox spline drive and lock ring, The thrust bearing and lock ring, the gear wheel which drives the c,m ring reduction gears, the cam ring with it's internal gear and bronze bearings, the supercharger drive gear and lock ring, the accessory gearbox drive tailshaft, and finally the accessory skew gear and starter dog. The crankshaft is in two parts held tightly together by the large pinch bolt. You can also see the two 4mm ground rods used to align both halves of the crankshaft after the master conrod ihas been fitted.


(https://lister-engine.com/coppermine/albums/userpics/10013/P1070913.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070914.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070915.JPG)

The last tree images show the crankshaft components loosely assembled. That slender tailshaft performs several functions, it drives the accessory gearbox, it connects the starter to the crankshaft and it also conducts the flow of lube oil supply from the pressure oil pump which is located at the rear of the engine, to all the crankshaft bearings. You can see some of the oilway drillings at the rear of the tailshaft

They say the devil is in the detail, but sometimes I begin to think it's the amount of detail, which is the Devil.

Stay tuned

Mike

Title: Re: Bristol Mercury revisited
Post by: Johnmcc69 on January 17, 2020, 11:32:33 PM
WOW!
That's a beautiful little assembly! Great job on the machining of it!

 That gives "fiddily" bits an entirely different meaning...

  :NotWorthy:

 John
Title: Re: Bristol Mercury revisited
Post by: Vixen on January 19, 2020, 02:32:28 PM
Thanks for calling in John. Here are some more 'fiddly' bits for you.

The connecting rod arrangement for most radial and rotary engines are all similar in concept. It consists of a Master rod to which eight Slave rods are attached. Here you can see some of the conrods for the Bristol Mercury engine. To make the hub of the Master rod as compact as possible ( to minimise geometric errors), bronze bushed bearings are used. Note, the big end of the Slave rod is actually smaller in diameter to the piston wrist pin. That shows how important it is to achieve a compact design.

(https://lister-engine.com/coppermine/albums/userpics/10013/01091906small.JPG)


This is the Master rod, you can see the eight lugs for the Slave rod bearing pins. The two lugs, either side of the main rod, are deeply recessed. This presented a problem during manufacture. I devised an offset grinding fixture for my Dremmel. The grinding head rotates about the Slave rod pin's axis centre, this allows the undercut to be ground away as the grinder swings from side to side.

(https://lister-engine.com/coppermine/albums/userpics/10013/01091908small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/01091224small.JPG)


Here you can see the Master rod big end bearing. The cylindrical part of the bearing is generously perforated to allow free flow of the lubricating oil, it bearing is free to float and rotate about the crankshaft pin and also inside the Master rod. Theoretically it could rotate at about half the engine speed. The end faces of the big end bearing have channels to direct  lubricating oil out to the eight Slave rod bearing pins.

(https://lister-engine.com/coppermine/albums/userpics/10013/P026small.JPG)


Here is the Master/Slave rod assembly installed onto the crankshaft. That huge pinch bolt clamps the two halves of the crankshaft together. There are no keways to maintain alignment, it is totally reliant on the clamping force alone.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070490~0.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070486~0.JPG)


Here the crankshaft and con rods are being trial fitted to the two piece crankcase. A single cylinder and piston have been added so that the fore and aft position of the rotating parts can be checked and adjusted to ensure the outer ends of the rods are central within each piston. As you can see, it's all very tight within the crankcase. Not a lot of room for adjustments

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070921small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070919small.JPG)



The next items for installation are the cam ring and the eighteen roller cam followers which fit all into the front section of the crankcase.

So stay tuned

Mike

Title: Re: Bristol Mercury revisited
Post by: crueby on January 19, 2020, 04:28:03 PM
Oh. My.   That is both fascinating and stunning.
Title: Re: Bristol Mercury revisited
Post by: fumopuc on January 19, 2020, 05:12:19 PM
Hi Mike, following along speechless.

Title: Re: Bristol Mercury revisited
Post by: scc on January 19, 2020, 09:30:19 PM
Exquisite :praise2:        Terry
Title: Re: Bristol Mercury revisited
Post by: steamer on January 19, 2020, 09:35:51 PM
Beautiful work Mike!!!!! :praise2: :praise2: :praise2: :praise2: :praise2: :praise2: :praise2: :praise2: :praise2:
Title: Re: Bristol Mercury revisited
Post by: Craig DeShong on January 22, 2020, 12:34:51 AM
Love’in it Mike  :popcorn: :popcorn:
Title: Re: Bristol Mercury revisited
Post by: michelko on January 22, 2020, 12:15:59 PM
You are for sure an real Artist  :NotWorthy:

Regards Michael
Title: Re: Bristol Mercury revisited
Post by: cnr6400 on January 22, 2020, 03:24:34 PM
Mike,  :ThumbsUp: :ThumbsUp: :ThumbsUp: :popcorn: :popcorn: :popcorn:
Title: Re: Bristol Mercury revisited
Post by: Vixen on January 22, 2020, 07:59:33 PM
Thank you everyone for dropping in and leaving such nice comments. They are very much appreciated and rewarding. Seems to make the effort worthwhile. :happyreader:

The weather was fine and dry today, which gave me the opportunity to spray paint the outside of the crankcase. My preparation starts with washing the parts with clean cellulose thinners. The thinners quickly removes any cutting fluid residues and greasy fingerprints. I am always amazed at how dirty the liquid becomes while cleaning what appears to be perfectly clean metal. The down side is the smell which lingers in the air for days.

I always preheat the parts to be painted and also the rattle cans, by placing them on a warm radiator for half an hour. This ensures the paint will dry quickly and the propellant is at optimum pressure to produce a fine and even fan (aerosol) of paint. I apply a thin base coat of light grey acid etch primer, which makes the top coat stick like glue to the aluminium. The primer coat is allowed to dry thoroughly before I add two or three thin layers of satin black acrylic car paint. I find the rattle can paint from Halfords (a UK motor parts supplier) to be adequate. The spayed parts are allowed to dry and left to harden overnight. Needless to say there is a lot of masking off required to shield those parts which are to be left as bare metal.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070924small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070925small.JPG)


All of the Bristol engines were painted with black enamel to prevent corrosion and supposedly to help with heat radiation.

The crankshaft and conrod assembly was reinstalled in the crankcase before I set about assembling the cam ring and the eighteen roller cam followers. The front cam ring has four lobes and drives the inlet valves, the rear ring drives the exhaust valves. The cam ring turns at 1/8 crankshaft speed driven by a simple spur gear reduction set. Each roller cam follower has a phosphor bronze wheel running on a hardened steel pin within a forked steel pushrod which slides in a bronze bearing. It was a seemingly endless task to make all these parts for my two Bristol Mercury engines.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070922small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070923small.JPG)


Here you can see the results of today's work. The crankshaft and camshaft are now finally installed within the crankcase and everything rotates nice and smoothly. Along the way I discovered a broken M1.5 tap in one of the 36 cam follower bolt holes, I must have broken the tap years ago but had completely forgotten about it. I don't think there is much I can do to extract it other than to use a miniature spark eroder but that would mean stripping everything down and giving the EDM job to a local engineering firm. Bummer !!!

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070926small.JPG)


I will make a daylight photo to replace the last one, provided the weather is still dry tomorrow morning.

Stay tuned

Mike
Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on January 22, 2020, 09:58:02 PM
Oh man what a bummer ... and thank God that this will not have any influence on running this beauty  :praise2:

Besides this, I'm completely out off superlatives for this build Mike .... :cheers:

Per
Title: Re: Bristol Mercury revisited
Post by: Rick Doane on January 22, 2020, 10:49:13 PM
Mr. Mike:

You Sir are an Artist!

Best Regards...….Rick
Title: Re: Bristol Mercury revisited
Post by: zeeprogrammer on January 22, 2020, 10:51:17 PM
...I'm completely out off superlatives for this build Mike .... :cheers:

Yeah and you're not the only one. Time to repeat...awesome!
Title: Re: Bristol Mercury revisited
Post by: Art K on January 23, 2020, 03:30:02 AM
Mike,
the crankcase and rod assembly look great, what more can I say. To bad about the broken tap though.
Art
Title: Re: Bristol Mercury revisited
Post by: petertha on January 23, 2020, 06:06:16 AM
Beautiful work as always, Mike.

I'm guessing your ring gear / cam was machined from solid as one integral part? Has this component been hardened either through or locally on the cam face? What material was used?

A more obscure design question. Some radials have what I think is called 'compensated' hole positions for the link rods on the master rod. In other words slight deviation to nominal equal spacing: 365 deg / number cylinders. The 5-cylinder I'm working on has that, the intent I'm led to believe is to achieve equal compression ratio (since its glow ignition & CR is important). Others have equal spacing but head mods to achieve equalized CR since the resultant throws are slightly different among cylinders. How does the Bristol fit into this? What about ignition - is the timing exactly equal with crank rotation, or phasing varies slightly by cylinder?
Title: Re: Bristol Mercury revisited
Post by: Steamer5 on January 23, 2020, 07:09:11 AM
Mike,
 I’m just lost for words!
But sure enjoying following along!


Cheers Kerrin
Title: Re: Bristol Mercury revisited
Post by: cnr6400 on January 23, 2020, 10:10:54 AM
Beautiful work as always, Mike.

I'm guessing your ring gear / cam was machined from solid as one integral part? Has this component been hardened either through or locally on the cam face? What material was used?

A more obscure design question. Some radials have what I think is called 'compensated' hole positions for the link rods on the master rod. In other words slight deviation to nominal equal spacing: 365 deg / number cylinders. The 5-cylinder I'm working on has that, the intent I'm led to believe is to achieve equal compression ratio (since its glow ignition & CR is important). Others have equal spacing but head mods to achieve equalized CR since the resultant throws are slightly different among cylinders. How does the Bristol fit into this? What about ignition - is the timing exactly equal with crank rotation, or phasing varies slightly by cylinder?

365 deg for equal spacing? I'm sure you meant 360 degrees. If you did use 365 for a spacing calculation you could get some wonky results!   :'( Just saying...... :cheers:
Title: Re: Bristol Mercury revisited
Post by: Vixen on January 23, 2020, 12:59:31 PM
Once again, thanks for all your generous comments and a particular thanks to pertertha for his two interesting question. That really made my day, one is very practical and the other touches on detail radial engine design principles.

Regarding the constriction of the Cam ring. The full size engines would have been machined in one piece using a gear shaper/ planer to cut the internal gear teeth. I do not possess a gear shaper/ planer, nor have I ever seen one other than in photographs. But I do know a man who has one !!  I went to HPC gears and bought a stock internal gear with the required number of teeth and correct pitch. I machined the four inlet cam lobes on the outside of the stock gear and attached that to the cam ring hub which had the other four exhaust cam lobes. Both the gear and the cam lobes are unhardened, the cam ring runs a 1/8 engine speed and has roller followers, so wear is not a major consideration.

(https://lister-engine.com/coppermine/albums/userpics/10013/DSCF0042small.JPG)



Regarding 'compensated' slave pin positioning. ALL radial engines employing the Master/ Slave conrod principal are fundamentally flawed by the geometry of the Master Slave link combination.  Only one piston, the piston in the Master rod cylinder moves in a symmetrical up and down motion. The remaining pistons move in a non-symmetrical manner due to the offset position of the Slave link pin position. As a result the piston movement has small positioning errors in timing and position. Due to the linkage geometry the errors are different for each Slave cylinder. Those adjacent to the Master rod have the least error while those further away on the opposite side of the Master rod have the greatest error. It is possible for a piston to arrive at the firing point ( Note I did not say TDC) 1,2,3,or even 4 degrees ahead or behind the theoretic position (360/ number of cylinders). The amount of error depends on the design geometry of the engine in question.

There are several ways to minimise the geometric errors. The angle between the Slave pin locations can be displaced radially, or the offset (throw) of the Slave pin can be adjusted in and out. However, because the fundamental cause of the piston positional error is due to the offset positions of the Slave pins, designing the diameter ring of Slave pin centres to be as small as possible will always lead to the smallest errors.

The Bristol Mercury is a nine cylinder radial, therefore the ring of Slave rod pins surrounding the Master rod is very crowded, There is little scope for angular position compensation without increasing the diameter of the Slave pin centres. Angular position compensation is always much easier on a 7 cylinder of 5 cylinder radial. If you look again at the drawings of the Mercury engines Master/Slave rod assembly, you will see Bristols answer to the problem. They designed the whole assembly to have as small a Slave pin centre diameter as possible simply making diameter of the Slave pin small to achieve the smallest and most compact hub. The Slave pin diameter is noticeably smaller than the wrist pin diameter, this leads to the smallest possible Slave pin centre diameter for this size of engine. Bristols also moved the offset (throw) of the Slave pin slightly to compensate (correct) the CR of each cylinder. The throw offset difference  are only a few thou, too small to be seen of the assembly drawing.

(https://lister-engine.com/coppermine/albums/userpics/10013/01091906small.JPG)



Radial engine design is always going to be a compromise. In the case of the full size Bristol Mercury, which was comparatively slow revving ( 2500 RPM max) with a low compression ratio ( 6.2:1) burning low grade 87 octane petrol; the flame front in each of the 5.75 inch diameter cylinders took some time to propagate across the whole cylinder, so small timing errors of a few degrees were of little or no consequence. The magnetos fired the spark at 390/9 =  40 degree intervals whereas the individual pistons may have been a few degrees out in arriving at the ideal firing point. It did not seem to matter.

Let's leave it there, if we can. This subject has been discussed at great length in a number of other publications and I really dont want to get into a deep theological discussion on the rights and wrongs of radial con rod design.

Cheers

Mike
Title: Re: Bristol Mercury revisited
Post by: AVTUR on January 23, 2020, 05:46:59 PM
Mike

Thanks for the description of the geometric problems of the master and slave rod assembly. I don't think I have seen it explained before (I read Fedden's book a long time ago and it may have been explained in there - I should take a look).

A few of us at Bristol Rolls-Royce Heritage Trust recognise the problem but really know nothing about it or its implications. I have a feeling that it was ignored for the valve/sleeve timing.

Can I please take a copy of your post to question the lads at RRHT next week? We will keep the discussion to ourselves.

AVTUR
Title: Re: Bristol Mercury revisited
Post by: Vixen on January 23, 2020, 06:19:50 PM
Hello AVTUR.

Good to hear from you again. I am also a life member of the Bristol Rolls-Royce Heritage Trust but it's all new faces there these days Most, if not all, of my original piston engine contacts there have long departed leaving only the new generation of gas turbine whizz kids.

Feel free to discuss the subject with the lads at RRHT next week and show them my input if you feel it's appropriate.

My understanding is the sleeve valve Hercules (two rows, each of severn cylinders) had enough room for the designers to employ some angular compensation. If you could find a copy of the Hercules Master rod machining drawings in the archive, it would be very revealing as regards to the hole centres for the Slave pins. Let me know if you can find the information, I would dearly like to know the real numbers.

I was only kind of half joking about further discussions. The subject was done to death in 'Strictly I/C magazine' a number of years ago and ended with lots of fruitless, uninformed opinions.

Cheers

Mike
Title: Re: Bristol Mercury revisited
Post by: petertha on January 23, 2020, 07:31:57 PM
365 deg for equal spacing? I'm sure you meant 360 degrees.

Thanks for the catch, cnr6400. Obviously nothing to do with the Gregorian calendar so I'll blame it on MS-Office 365, its apparently invading my subconscious thoughts! LOL
Fortunately Mike saw past my typo and knew what I meant. Thanks for the detailed reply.
Title: Re: Bristol Mercury revisited
Post by: Roger B on January 24, 2020, 11:49:57 AM
Wonderful  :praise2:  :praise2:  Most of the pictures could be of a full sized engine  :ThumbsUp:  :ThumbsUp: It's only the picture with the spray cans that gives the size away  :wine1:
Title: Re: Bristol Mercury revisited
Post by: Craig DeShong on January 26, 2020, 01:46:24 AM
Wonderful  :praise2:  :praise2:  Most of the pictures could be of a full sized engine  :ThumbsUp:  :ThumbsUp: It's only the picture with the spray cans that gives the size away  :wine1:

And I thought they were GIANT spray cans  :lolb:

Superb as always Mike.
Title: Re: Bristol Mercury revisited
Post by: Vixen on January 26, 2020, 08:33:56 AM
Wonderful  :praise2:  :praise2:  Most of the pictures could be of a full sized engine  :ThumbsUp:  :ThumbsUp: It's only the picture with the spray cans that gives the size away  :wine1:

They may not be spray cans at all. Think of them as miniature 50 gallon oil drums. :lolb:

Mike
Title: Re: Bristol Mercury revisited
Post by: Vixen on January 29, 2020, 03:02:46 PM
I have made some more progress with assembling the second Bristol Mercury engine. However, I have been severely distracted by the arrival of my 'Cheap as chips' 3D printer.kit.

In the first photo you can see the previously assembled crankcase core together with the thrust bearing housing, which contains the  cam gear reduction gears and the breather system, among other things. Also to the left of the photo, are the reduction gearbox and variable pitch propeller hub.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070935small.JPG)


The second photo shows the thrust bearing housing loosely assembled to the engine core. You can clearly see the splined drive on the end of the crankshaft, this engages with the splined drive coupling on the input side to the reduction gearbox.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070934small.JPG)


The final photo of a totem pole  is actually all the above units loosely assembled. I have been able to identify and measure the thickness of the shims required to make the two splined drive components mesh correctly.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070933small.JPG)


If I had not fallen down the 'Cheap as chips' 3D printer rabbit hole, I would have had the shims made and assembled by now

Stay tuned

Mike

Title: Re: Bristol Mercury revisited
Post by: Jo on January 29, 2020, 05:13:57 PM
If I had not fallen down the 'Cheap as chips' 3D printer rabbit hole, I would have had the shims made and assembled by now

 :facepalm:  :ShakeHead:   :-X

Jo
Title: Re: Bristol Mercury revisited
Post by: Vixen on January 29, 2020, 05:39:18 PM
If I had not fallen down the 'Cheap as chips' 3D printer rabbit hole, I would have had the shims made and assembled by now

 :facepalm:  :ShakeHead:   :-X

Jo

OK, we all knew it would happen that way  :lolb: :lolb:

But as you say "Enjoyment is more important than achievement".


Mike
Title: Re: Bristol Mercury revisited
Post by: Vixen on February 04, 2020, 05:23:56 PM
I've returned from a new world of 'material addition' playing with my new 'cheap as chips' Chinese 3D printer, to the more familiar, real world of 'metal removal' using the mill and the lathe

I have now got as far as fitting the pistons to my second Bristol Mercury. Here you can see the pistons after they and the conrod bush bearings have been reamed to size for the wrist pin.. The nine cylinders are waiting in the background for their turn to play.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070945small.JPG)


Here are the cylinders in place. It's looking like the job is completed. But NO, 'Houston we have a problem',  the engine won't turn over. Several of the piston skirts are clashing was they pass BDC. I have forgotten one small, but essential, machining stage; the tiny 20 degree flats on the bottom of each pistol skirt.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070943small.JPG)


This is the way I made the pistons. I started with three blocks of 6082 alloy, enough to make 21 pistons, thats 18 for the two engines and a few 'just in case'.

I took the unusual approach of machining the complete interior detail of each piston while they were all attached to the billet. I used a very long 3mm ball nose cutter to create a nicely radiused pocket, without sharp corners, to eliminate the risk of crack propagation. I prepared one g-code program to machine the internal features of a single piston, then indexed along the block, reset the zeros and repeated the machining of next pocket before indexing again, machining etc. You can see I even drilled some of the oil holes before the blocks were cut up and waste material removed using the bandsaw.

(https://lister-engine.com/coppermine/albums/userpics/10013/2001_1218_104446AAsmall.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/2001_1222_021555AAsmall.JPG)


I made a special chucking fixture to turn the piston crown and outside diameter. The outer edge of the fixture registers on the pistons inside diameter which holds everything nice and concentric. I used a the little tubular piece to hold each piston in position with pressure from the rotating centre in the tailstock. The pistons were all left oversize, so that they could be individually matched to each of the cylinders. Here we can see the 18 pistons, complete with oil control ring and compression ring grooves, awaiting the next stage. There are now only two spare pistons available if required as one was lost due to a depth of cut set-up error.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070937small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070939small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/2002_0111_060630AAsmall.JPG)


I did not manage to achieve identical in bore diameters for the nine cylinders, but they are within a few thou of each other. To compensate, I finish turned a piston to match each individual cylinder. I took slow feed rate cuts with a one thou DOC until I achieved  a 2 to 3 thou clearance between a piston and it's paired cylinder. This process produced masses of fine angle hair swarf.

There was one final machining operation required, which I had completely failed to remember to do. It's necessity revealed itself after the cylinders barrels were added and the engine failed to turn over. I discovered that the skirts of the pistons were colliding and needed a small amount of material to be removed, to prevent contact with their neighbors as they passed BDC. The chamfers are clearly shown on my drawings but somehow I managed to ignore them. You can see the cylinders already have a 20* chamfer on either side of their skirt, to prevent them touching each other deep inside the crankcase. The pistons also need a similar 20* chamfer to prevent clashes.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070943small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070949small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070947small.JPG)


Each piston was held in an angle vice set to 20*. A long ground bar was passed through the wrist pin bosses and supported on a pair of parallels. About 20 thou of material was removed from each side.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070950small.JPG)

Interestingly, the piston skirt collisions only occurred in the cylinders opposite side to the Master rod. This clearly demonstrates how the reciprocating motion of a radial engine's pistons differs with individual cylinders due to the Master/slave rod geometry. The greatest geometric errors always occur on the side opposite to the Master con rod.

There's more to come, so stay tuned

Mike
Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on February 04, 2020, 09:28:16 PM
Very nice and I really like the idea of milling the internals the way you did it (trying to remember this later) ...

You leave out a very important detail - how did you do the piston pin holes and how did you make sure they are exactly 90 degrees to the bore ?

Quote
the tiny 20 degree flats on the bottom of each pistol skirt.

I know some engines backfire and I've heard about single stroke engines - but how do you "cock this one" Mike  ;)
Title: Re: Bristol Mercury revisited
Post by: cnr6400 on February 04, 2020, 10:11:23 PM
Great work Mike!  :ThumbsUp: :ThumbsUp: :ThumbsUp: :popcorn: :popcorn: :popcorn:
Title: Re: Bristol Mercury revisited
Post by: Vixen on February 04, 2020, 11:09:33 PM
Thank you both for calling in.  :ThumbsUp:

I guess if anyone were to find that typo it would be Per. You old son of a gun :ROFL:
A word of warning for you. NEVER look down the barrel of a cocked revolver and pull the trigger, just to see how it works.  :lolb:

As for cross drilling the piston. There are several ways to do it accurately. I chose to bolt a Vee block square to the mill table. I strapped the raw piston to the Vee block with the internal pin lugs set horizontal. I used a centre finder to touch off both sides of the cylinder (piston), divided by two and moved the quill over TDC. I touched off the bottom of the piston skirt and moved up the appropriate amount. I used a end cutting mill cutter to drill the cross hole, because it was less likely to wonder off axis. I clamped a offcut of plate to the Vee block to act as an end stop; then it was a simple job to position the rest of the pistons. I was probable so excited at another job completed quickly, that I forgot the photos...  Sorry

Regards

Mike
Title: Re: Bristol Mercury revisited
Post by: Roger B on February 09, 2020, 08:04:25 AM
That was an interesting way to machine the pistons  :ThumbsUp:  :ThumbsUp:  :wine1:
Title: Re: Bristol Mercury revisited
Post by: Vixen on February 09, 2020, 11:28:06 AM
That was an interesting way to machine the pistons  :ThumbsUp:  :ThumbsUp:  :wine1:

Hello Roger,

It may be interesting and it may be a different way to machine the pistons, but it is not necessarily a better way. It suited my purposes at the time, because back then, I did not have any other accurate means of mounting a round billet vertically on the mill table.   Needs, must, as they say

Mike
Title: Re: Bristol Mercury revisited
Post by: fumopuc on February 09, 2020, 11:34:20 AM
Hi Mike,
Indeed  a very interesting way to make pistons.
I have to file it away.
Thanks for showing it.
Title: Re: Bristol Mercury revisited
Post by: petertha on February 09, 2020, 04:37:38 PM
Mike> I did not manage to achieve identical in bore diameters for the nine cylinders, but they are within a few thou of each other. To compensate, I finish turned a piston to match each individual cylinder.

Hi Mike. Will the ring making (dimensions) be common to all cylinders or will you have to make a few dedicated matched ones there too? Can you give me an idea of typical clearance (piston OD vs bore ID).

I went back through the posts & didn't see mention of lapping or grinding. I wasn't sure f that was already behind you or forthcoming. Anyways, I'm curious about your preferred methods, how you transition from boring / reaming? to final bore size & finish.
Title: Re: Bristol Mercury revisited
Post by: Vixen on February 09, 2020, 06:09:36 PM
Hi petertha,

The title of this thread is Mercury revisited. I am only reporting on current activities with these two engines, the original work was undertaken many moons ago.

I finish turned the bore of nineteen cylinders on the lathe to the best accuracy and finish possible on my old, worn out, Colchester Chipmaster. I selected the best nine cylinders with near identical bore sizes for one engine leaving a collection of cylinders with a spread of bore sizes for the second engine.

I made a 'Delapina' like honing tool with expanding stones, to make the cylinders round , parallel (no barreling) and smooth. I did not have a very efficient way of expanding the stones in the hone, unlike a real Delapena; so the rate of metal removal was very, very slow. The first engine's cylinders were almost identical in diameter but the second engine had a spread of a few thou. I just did not have the time (days per cylinder) or enthusiasm to bring them all to the same size. Since then, I have discovered that our Jo has a real Delapena hone, which she calls 'Mr Smelly'. If only I had been able to use that way back then.

I will have to make individual rings in the same way I matched the pistons to fit individual cylinders. I's a bit of a pain as I will have to make enough spares of different sizes to cater for breakages. The pistons are nominally 1.38" diameter (35mm) and are machined to be 2 thou undersize. A piston, without rings, will drop slowly down a sealed  cylinder bore, when held vertically, in about  ten to twenty seconds.

Mke

Title: Re: Bristol Mercury revisited
Post by: Vixen on February 11, 2020, 04:35:31 PM
I've got a lot of studs to make to hold down the Mercury's cylinders to the crankcase, eight studs per cylinder. I need an an accurate method to cut the stock to the required length and make a neat cut. I needed something better than the bench vice and hacksaw.

Today I made this tiny cut off saw out of an old Dremel flexi extension and a few bits from the scrap box, It is so simple it hardly needs an explanation of how it was made. The clamp for the Flexi extension was made for a previous job on the Master conrod. It has been laying about unused for years. The body was made from some 1/2" ally offcuts and is intended to be held in the bench vice. There is a V grove and clamp plate,to hold a variety of sizes of small stock. On the right side is an adjustable end stop made from some 4mm threaded rod and a large diameter washer.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070956small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070957small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070959small.JPG)


So simple and so effective. The only difficulty is finding the offcut on the floor, after it has been chopped from the stock. I feel a magnet is going to help here.

Mike
Title: Re: Bristol Mercury revisited
Post by: Steamer5 on February 11, 2020, 08:58:35 PM
Hi Mike,
 Nice chop saw!
Can see a certain lady come visiting you to get her stud collection upto date! I’m sure that mods to it wouldn’t be to hard to over engineer it.

Cheers Kerrin
Title: Re: Bristol Mercury revisited
Post by: deltatango on February 11, 2020, 09:05:22 PM
Thanks for that idea Mike,

Faced with several hundred studs to make for the Tandem Compound Mill Engine new ideas are very welcome! I think I'll be making something similar, i already have the Dremel flex extension etc.

David
Title: Re: Bristol Mercury revisited
Post by: crueby on February 11, 2020, 09:33:34 PM
I've done basically the same thing for making mass quantities of studs, using one of the little hobby chop saws and a abrasive blade, just had to cobble up a length stop next to the vise. Had to give each a twirl on the belt sander to smooth the bur at the end. Great way to do it.
Title: Re: Bristol Mercury revisited
Post by: awake on February 11, 2020, 09:49:02 PM
Vixen, the quality and complexity of the work in this engine is mind-boggling to me. Truly magnificent! And I love the creative machining set-ups. Seeing pictures like this is extra helpful in thinking about how to solve machining challenges. I am in awe of your ability!  :NotWorthy:

And having said that, I hate to indulge in the following ... but since you took such pains to correct "piston" in the partially quoted post below, I just have to wander about another word in that post - seemed like you might be wondering away from the correct spelling. ;D

As for cross drilling the piston. There are several ways to do it accurately. I chose to bolt a Vee block square to the mill table. I strapped the raw piston to the Vee block with the internal pin lugs set horizontal. I used a centre finder to touch off both sides of the cylinder (piston), divided by two and moved the quill over TDC. I touched off the bottom of the piston skirt and moved up the appropriate amount. I used a end cutting mill cutter to drill the cross hole, because it was less likely to wonder off axis.
Title: Re: Bristol Mercury revisited
Post by: Vixen on February 11, 2020, 10:07:33 PM

And having said that, I hate to indulge in the following ... but since you took such pains to correct "piston" in the partially quoted post below, I just have to wander about another word in that post - seemed like you might be wondering away from the correct spelling. ;D

Andy

Touche Andy,

I blame it on the smell chucker or should that be the Spell Checker

Mike
Title: Re: Bristol Mercury revisited
Post by: awake on February 11, 2020, 11:28:26 PM
So-called auto-correct is what gets me, time after time. Clearly the computer does NOT know how to read my mind ... :)

I don't want my poor attempt at humor to distract from the more important point - your work and presentation thereof. I am in progress with my first IC engine (a modified Webster), and am astonished at the number of small, fiddly parts. A 9-cylinder radial is way, way beyond anything I can imagine tackling. Two thumbs up for your work!
Title: Re: Bristol Mercury revisited
Post by: Vixen on February 23, 2020, 09:19:36 PM
So, back to the build of the second Bristol Mercury. In this instalment form Vixen's den we have reached the point of installing the cylinder heads on top of the nine cylinders.

During manufacture, at the Bristol's factory, the aluminium cylinders heads of the full size engines were screwed and shrunk into the steel cylinder barrels at an early stage. The joint was sealed by crushing a copper washer. The bolt holes in the cylinder base were drill after the head had been attached and had passed a pressure test. I have been attempting to build my 1/4 scale engine in exactly the same way using the original works drawings wherever possible. For various reasons, I did not permanently attach the cylinder heads as early as they did in the Bristol's factory. I do not have the facilities (or courage) necessary to attempt to make a permanent shrink fit. I would have to settle for a standard thread clearance. The model's cylinders and cylinder heads were paired off and numbered, the base flanges were drilled allowing for a further 1/8 of a turn during final assembly, to torque up the joint and to crush the copper washer.

Here you can see a cylinder set awaiting final assembly.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070964small.JPG)


The piston is positioned within it's matching cylinder with the piston crown standing slightly proud. This is to centralise the copper crush washer. The cylinder thread and the cylinder head have been painted with copper anti seize grease. The copper grease serves two purposes, it prevents the thread galling during tightening and it also helps improve the heat conduction between the cylinder and the head. The cylinder assembly is nipped up, hand tight, before being transferred to my partially flooded workshop for final tightening and alignment

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070962small.JPG)


Here are the very basic tools I use to tighten the cylinder assemblies. The peg spanner was made from alloy plate from the scrap box, The long edge is aligned to the axis of the cylinder. The two comb like blocks fit inside the fins on the cylinder head to allow it to be held in the big workshop vice without damaging the cylinder heads.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070965small.JPG)


The cylinder/ head is tightened (1/8 turn) to crush the copper washer, until the long edge of the peg spanner aligned with the cylinder head fins. A little brute force, with a nylon faced hammer, was sometimes required to flog the joint into alignment.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070966small.JPG)


It was a tremendous relief to have successfully assembled all of the cylinders without incident. It was then a simply a case of fitting the pistons and wrist pins to the appropriate conrods and bolting down the cylinders. However 9 cylinders each with 8 base bolts equates to a lot of tiny nuts to fit and tighten. Access was good at the beginning but things got tighter as more and more cylinders were added. There are times when 1/4 scale fingers would be better than the ones God gave me.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070969small.JPG)


You may be interested in how the cylinder heads were made. It all started with the arrival of a 36" long bar of 3"diameter 6082 T6 alloy. The bar was chopped up into 20 hockey puck sized lumps, one for each cylinder head. I needed 18 cylinder heads for my two Bristol Mercury engines, I anticipated there may be manufacturing problems along the way, so optimistically hoped I would get away with a minimum of two spares.

The 20 cylinder heads would be made as one big batch. All of the heads would progress through the various machining operations, step by step. A failure in any one step would mean a failure of the whole batch, so measure twice ( even three or four times)  then cut once.

The first operation was to face all the embryo heads to length. The cylinder heads were then transferred to my rotary table. The quill on my old Dore Westbury mill was set over at 30 degrees and centred on the bottom of the combustion chamber recess, ready to machine the valve pockets.

(https://lister-engine.com/coppermine/albums/userpics/10013/HEAD01.jpg)


The positions for the four inlet and exhaust valves were bored and threaded using in the mill, indexed by the rotary table. The heads were then transferred to the lathe for the more thread cutting and the profiling of the lower, circular, portion of the cylinder fins.

(https://lister-engine.com/coppermine/albums/userpics/10013/HEAD07.jpg)

(https://lister-engine.com/coppermine/albums/userpics/10013/HEAD09.jpg)


Then back to the mill for more profiling of the inside of the combustion chamber. It's very tight in there with two spark plugs and four valves forming the penthouse combustion chamber.

(https://lister-engine.com/coppermine/albums/userpics/10013/HEAD10.jpg)


Here is head #15 of 20 back on the mill for the first of a number of milling operations to form the flats on the upper half of the cylinder head.

(https://lister-engine.com/coppermine/albums/userpics/10013/HEAD11.jpg)

(https://lister-engine.com/coppermine/albums/userpics/10013/HEAD14.jpg)


Here is a cylinder head nearing the end of the milling operations. Bristol's did the all these operations in one big hit, using a gang of profiled cutters mounted on the spindle of a huge horizontal milling machine. The outside shape of the cooling fins is now complete. I cannot put off the next step any longer.

(https://lister-engine.com/coppermine/albums/userpics/10013/HEAD19.jpg)


Next was the nail biting moment. Deep fins had to be cut around the base of the cylinder head and also for and aft in the upper half. I mounted each cylinder head on a dummy cylinder, again located in my faithfull old rotary table. I made up a gang of seven slitting saws to cut slots 35 thou wide with 25 thou spacers in between. The 7 slitting saws were selected  from a collection of ten saws, each of the same nominal width. It is amazing how good the human eye is at spotting a saw which cuts a slightly wider than the others.

The gang of slitting saws was plunged full depth into the cylinder blocks and the head slowly rotated on the rotary table until the fin slots were cut full circle. The fins look so delicate with disaster about to happen at any moment; but in reality the saws are cutting into a solid lump of high quality material, the delicate fins see no cutting forces and are merely being left behind. The biggest issue was chip clearance. I ended up using the biggest available suds pump, surrounded by a jury rigged tin late dam to try to contain the resultant spray. The spray of suds (stinking stuff) went everywhere.


(https://lister-engine.com/coppermine/albums/userpics/10013/HEAD21~0.jpg)


Here you can see cylinder head #5 of 20 being held in the machine vice for the fore/ aft fins to be cut. Note the comb block inserted between the horizontal fins, it holds the cylinder head firmly in the machine vice without marking or damaging the head.

(https://lister-engine.com/coppermine/albums/userpics/10013/HEAD23~0.jpg)


The result of a full year's nail biting work lined up on parade. The result, 18 near perfect cylinder heads, one reasonable one as a spare and only one casualty, which was partially sectioned to check on remaining wall thicknesses under the fins. That particular head was the crash dummy and was the one used to test and prove each operation before proceeding with the east of the batch.

(https://lister-engine.com/coppermine/albums/userpics/10013/HEAD25.jpg)


The build of the second engine is proceeding well, the end is in sight.

Stay tuned

Mike
Title: Re: Bristol Mercury revisited
Post by: zeeprogrammer on February 23, 2020, 10:30:31 PM
I can't say much more than "Wow!".

Fascinating post.
Title: Re: Bristol Mercury revisited
Post by: petertha on February 23, 2020, 11:28:22 PM
Fantastic pictures and description, Mike.
Title: Re: Bristol Mercury revisited
Post by: gbritnell on February 24, 2020, 11:53:36 AM
Truly outstanding work Mike! It almost wants me to make another radial, this time 9 cylinders instead of 5.
I really enjoy your documentation and know how much work it is to stop and take pictures while you're making parts.
gbritnell
Title: Re: Bristol Mercury revisited
Post by: Vixen on February 24, 2020, 02:42:16 PM
Thank you all for calling in.  :ThumbsUp: :ThumbsUp: :ThumbsUp:

It is only the positive response of our MEM forum members that makes it feel worthwhile to continue to write and post build progress.

With the number of model shows on the decline, I look at the MEM forum as our virtual, on-line, model show, somewhere were we can all showcase our work to a worldwide audience of like minded individuals.

And George, if you want to build a nine cylinder radial, you had better start soon. They take an enormous amount of time and effort to complete and none of us are getting any younger.

Mike
Title: Re: Bristol Mercury revisited
Post by: Dave Otto on February 26, 2020, 12:45:16 AM
Amazing work Mike!
Its always fun to see an update on your projects.

Dave
Title: Re: Bristol Mercury revisited
Post by: Vixen on February 26, 2020, 01:58:11 PM
Dave
Thanks for your kind comment. It's also fun to be at the receiving end. :ThumbsUp: :ThumbsUp:

Mike
Title: Re: Bristol Mercury revisited
Post by: Vixen on March 10, 2020, 04:55:22 PM
Some more small detail work underway for the two Mercury engines. This time I have been casting spark plug caps in polyurethane synthetic rubber.

This has required some mould making and more kitchen chemistry.

Each engine requires 18 spark plug caps, so I decided it would be reasonably efficient to make them in batches of 6 at a time, this obviously means 6 moulds and several repeat casting sessions. I started by making the moulds in perspex (I do like that material) with turned aluminium inserts to form the cavities for the cable and the spark plug. The pespex part was made from two 10mm thick blocks clamped together and drilled from all directions to form the mould cavity for two individual spark plug caps. Aluminium inserts were turned and used to 'core' the moulds. File lines were engraved in the perspex from the ends of the casting to the base of the mould. A vacuum is applied during the casting process to draw the PU rubber into and completely fill the mould. You can see the suction base on the right and the cardboard gasket used to seal the mould to the suction base.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070992small.JPG)


The mould has been given a generous coating of furniture wax, inside and out, to act as a release agent. Here the first mould is clamped to the suction base, to which is attached the little hand vacuum pump I had previously used to test the valve seating on the Bristol Jupiter. Here we are all set-up and ready to go. We are either going to get some rubber spark plug caps or a lot of sticky goo. Fingers crossed

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070994small.JPG)


That's the engineering done, so here comes the kitchen chemistry. I bought a small two part PU casting kit; Mouldcraft PT-flex 85 PU casting rubber from a UK firm called Mouldcraft. Equal quantities of the two parts are required to be thoroughly mixed to make the PU rubber. I only need to mix a small quantity for each batch so I measured out equal quantities of the part A and part B in two small containers salvaged from some redundant fluorescent light starters. The two measures were mixed in a deep coffee powder spoon and mixed thoroughly.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070995small.JPG)


A small quantity of the mixture was poured into the funnel on the top of the mould, a couple of strokes on the vacuum pump pulled the resin into the mould. The clear perspex made it easy to see when the mould was completely filled. The funnel was topped up, the first mould was removed and allowed to cure while the next mould was attended to.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070996small.JPG)


The PU is supposed to cure in less than an hour but I left it overnight to be sure. Next morning, the mould was dismantled and the aluminium inserts removed with a twist and pull. The furniture wax released perfectly. The three moulds produced 6 plug caps, three were good and three had flaws. Not a bad yield for the first go round. The moulds were re-waxed and re-assembled ready for the next season. I hope to have learned a few lessons and the yield may be better next time round

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070990small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070991small.JPG)


The great thing about model engineering is the wide variety of challenges encountered. There is always something new to try.
And the great thing about the MEM forum are the members

Stay tuned

Mike

Title: Re: Bristol Mercury revisited
Post by: Roger B on March 10, 2020, 08:28:52 PM
Splendid  :praise2: Can I put in an order?
Title: Re: Bristol Mercury revisited
Post by: deltatango on March 10, 2020, 09:40:00 PM
Thanks Mike, that post is an inspiration! One more to add to the long list of inspirations from your work. When I built Mastiff and the Wyvern I did think about how to make realistic, and useful, plug caps but dismissed the idea as impractical - I was clearly wrong.

David
Title: Re: Bristol Mercury revisited
Post by: Vixen on March 10, 2020, 09:55:31 PM
Hello David,

Thanks  :ThumbsUp:, but there are a number of different ways to make nice looking plug caps. Have a look at Graham Meeks method. Starts about 1/4 the way down this page. https://modelengineeringwebsite.com/Miniature_spark_plugs_2.html

Cheers

Mike
Title: Re: Bristol Mercury revisited
Post by: deltatango on March 10, 2020, 11:30:20 PM
Hello Mike, Thanks, I hadn't seen Graham Meeks' work. His plugs and caps look entirely practical. If you need soft plug caps, e.g. to keep out water in a boat installation,  then molding from a soft(er) material may be better. Making, say, 18 plugs for a 9-cylinder rotary using GM's method looks more practical, and cheaper, than any other that I've seen.
David
Title: Re: Bristol Mercury revisited
Post by: Vixen on March 10, 2020, 11:48:54 PM
Hello David,

Quite so. I was impressed by Graham Meek's designs. I used his 'fish spine' spark plug design for the 1/3 scale Bristol Jupiter. I did a write up of the manufacture and test of these spark plugs in the 'By Jupiter' build log starting at reply #425 http://www.modelenginemaker.com/index.php/topic,7559.400.html.

And as you say, the soft PU plug caps are potentially (sic) more waterproof than GM's hard material caps. However most folk don't run their engines in the rain and wet.

Mike.
Title: Re: Bristol Mercury revisited
Post by: deltatango on March 11, 2020, 12:14:19 AM
Mike, I just followed that link and discovered (re-discovered) that I'd read it already  :-[ .

I can just about claim advanced age as an excuse but still!!

David
Title: Re: Bristol Mercury revisited
Post by: Vixen on March 11, 2020, 12:19:36 AM
David,

It's not the age but the mileage, which matters.

You going to the F1 this weekend?

Mike
Title: Re: Bristol Mercury revisited
Post by: 90LX_Notch on March 12, 2020, 12:38:32 AM
Mike-

I'm still following along and I am blown away by the quality of this build.

-Bob
Title: Re: Bristol Mercury revisited
Post by: deltatango on March 12, 2020, 05:23:09 AM
Hello Mike,
Only just read your last, I'm high (air) mileage but not too much wear as yet  :).

I've been to the Melbourne GP once and decided then that, whilst the noise is wonderful, you get to see much more of the race on TV. It's also a lot cheaper - OK I did grow up in Yorkshire...
David
Title: Re: Bristol Mercury revisited
Post by: Vixen on March 21, 2020, 02:16:50 PM
With all the new imposed self isolation and distancing, I expect we will all be using the forum more and more.

I will start off with an update of progress on the second Bristol Mercury. I have reached the point of assembling the rocker gear on top of the cylinders

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070974small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1070975small.JPG)

The front pushrod operates on the two front rocker arms, which in turn open the two inlet valves at the rear of the cylinder head. Similarly the rear pushrod operated the rear pair of rocker arms which open the two exhaust valves at the front of the cylinder head. The rocker gear control rod is between the two push rods.

As you can see, the rocker gear, which operates the four valves, is perched above the cylinder heads. The rear of the rocker gear is supported and free to rotate on two pillars located between the valve springs. At the front the rocker gear is attached to a control rod, which is tied to the crankcase, You can see the control rod between the two push rods. All the connections to the rocker gear are free to move. This was all part of Roy Feddon's (the designer) excessive attention to detail. Feddon calculated that the cylinders would expand in length when the engine was at working temperature, while the push rods would still be at outside air temperature and would not expand. The result would be a difference in tappet clearance between hot and cold. So Feddon devised this compensation linkage to minimise the tappet clearance difference. The geometry of the linkage ensured the tappet clearance 'error' was reduced by a factor of four.

This elaborate temperature compensation system was used on most of the Bristol poppet valve engines from the Jupiter to the Mercury and Pegasus. It was a cleaver approach but must have added a lot more to the cost of manufacture. Most other aero engine manufactures and virtually all auto manufactures use the simpler and less expensive approach of setting the tappet gaps wider when cold, so they become correct when working temperature id reached.

(https://lister-engine.com/coppermine/albums/userpics/10013/2005_0212Image0023small.JPG)


Below you can see the individual components of the rocker gear. The two sets of rockers are coaxially mounted on either side of the rocker box. THe full size engine had eight roller bearings in each rocker assembly. The model engine had to make do with eight phosphor bronze bushes

(https://lister-engine.com/coppermine/albums/userpics/10013/2005_0120Image0008small.JPG)


Production of eighteen sets (plus some spares) of rocker arms for the two engines was an endless, thankless task. It too a full year to fill these dog food tins with completed components for the two engines. I nearly gave up several times during that time.

(https://lister-engine.com/coppermine/albums/userpics/10013/2005_0120Image0032small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/2005_0120Image0034small.JPG)


Eventually, after all that work, I was able to build the nine rocker assemblies for the first engine.

(https://lister-engine.com/coppermine/albums/userpics/10013/2005_0120Image0015small.JPG)


Here you can see one of the rocker assemblies in position on top of a cylinder head. The rocker gear will be enclosed with a tight fitting cover to keep high altitude ice formation from interfering with the mechanism

(https://lister-engine.com/coppermine/albums/userpics/10013/2005_0212Image0024small.JPG)


Here are the rocker box covers in production. The top surface was profiled before the internal details were pocketed. The part finished covers were parted from the stock before the top front curved surface was filed and blended by hand

(https://lister-engine.com/coppermine/albums/userpics/10013/2005_03260002small.JPG)


Here are a batch of nine rocker box covers, destined for the second engine.

(https://lister-engine.com/coppermine/albums/userpics/10013/2005_03260003small.JPG)

All this is bringing the second engine near to completion. It was being prepared for this year's Model Engineer Exhibition at Doncaster in May. Unfortunately that's not going to happen. However, we still have the MEM forum. It's our worldwide virtual model engine showcase. So lets use that instead.

Stay Safe

Mike

Title: Re: Bristol Mercury revisited
Post by: cnr6400 on March 21, 2020, 03:00:12 PM
 :ThumbsUp: :ThumbsUp: :ThumbsUp: :popcorn: :popcorn: :popcorn:

Fascinating info on the valvetrain parts and design Mike. Great progress on the engine too! Thanks for sharing it.   :cheers:
Title: Re: Bristol Mercury revisited
Post by: nj111 on March 21, 2020, 03:17:27 PM
Phenomenal amount of complex work there Mike. It amazes me how you get so much done - compared to myself!  Please keep posting!
Title: Re: Bristol Mercury revisited
Post by: Vixen on March 21, 2020, 03:22:42 PM
Nick, Some of those photos go back 15 years or more. The two Mercury engines have been 'Work in Progress' for over 20 years. They stood collecting dust for several years before I came back to them. Hence the title 'Bristol Mercury revisited'.

Stay Safe

Mike
Title: Re: Bristol Mercury revisited
Post by: awake on March 21, 2020, 03:29:56 PM
The amount of work in this model is staggering - and the execution is absolutely brilliant! 20 years - now that's a lot of patience and dedication!
Title: Re: Bristol Mercury revisited
Post by: Roger B on March 21, 2020, 07:26:13 PM
Excellent  :praise2:  :praise2: I do tend to think that the expansion compensation for the valve clearances was solving a problem that didn't really exist  :thinking: Warm the engine up before putting it under load  :headscratch:
Title: Re: Bristol Mercury revisited
Post by: Vixen on March 21, 2020, 09:01:59 PM
Roger,

If you are going to solve a non-problem, then do it elegantly and expensively. The customers always fall for it.

Mike
Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on March 21, 2020, 09:10:06 PM
Quote
If you are going to solve a non-problem, then do it elegantly and expensively. The customers always fall for it.

 :lolb:   :ROFL:    :LittleDevil:  Ain't that the truth  :mischief:

Oh and I'm still lost for new words to hail your work Mike -> not many comments from me and strangely no questions either ....  :cheers:    :popcorn:

Per
Title: Re: Bristol Mercury revisited
Post by: Vixen on March 21, 2020, 09:15:31 PM
Quote from: Admiral_dk
not many comments from me and strangely no questions either ....  :cheers:    :popcorn:

Per

Oh! I was waiting for some questions. :stir: :stir:

Mike
Title: Re: Bristol Mercury revisited
Post by: kvom on March 21, 2020, 09:15:39 PM
Just catching up after 3 weeks traveling and a week of jet lag afterwards.  Impressive work there as well as the patience required which is in some respects more worthy of praise.
Title: Re: Bristol Mercury revisited
Post by: zeeprogrammer on March 21, 2020, 09:57:55 PM
The amount of work in this model is staggering - and the execution is absolutely brilliant!

Well put. Every time I take a look, I have to reach down and bring my jaw up.
Title: Re: Bristol Mercury revisited
Post by: petertha on March 22, 2020, 01:41:21 AM
Magnificent!
- roughly what is the size of these square holes & how did you broach them?
- I'm trying to get my head around the pushrod contact geometry. That is quite the funky motion. Is the end of the pushrod like a cone & the underside of the rocker pairs ball-ish shape? Anyways, how did you machine the rocker underside ball-ish shapes consistently part to part?
- how are these metal to metal sliding surfaces lubricated?

You'll see my 5-cyl radial build one day soon, I promise. Its quite Neanderthal by comparison. But just know that your work is providing lots of inspiration over the rough patches to keep perservering.
Title: Re: Bristol Mercury revisited
Post by: Vixen on March 22, 2020, 10:48:19 AM
Hello Perertha,

Thanks for calling in. Forums like this one will become increasingly important as we all lock down and isolate.

The full size engine used multi splined couplings on the inlet rocker arms. So for the model I substituted a simpler square drive. The square hole is only 0.12" ( 3.1mm) across the flats. I formed these by drilling and some file work before bringing the hole to size with a homemade square broach. I made several of these brooches from hardened and tempered silver steel (drill rod?) as they did not last for long.

The push rods, each have a mushroom shaped end pad with a spherical end face, hard as flint. Each rocker arm had a hardened spherical insert which was free to rotate. The contact between the three spherical parts provided some rotation. For the model, I considered the spherical inserts to be impractical, instead I machined a circular pad (viewed from the front) on each rocker arm, followed by some hand filing. So I have cylindrical to spherical contact.

The lubrication of this area was minimal on the fullsize engines. They relied on hard felt pads in the cover plate soaked in oil. The pushrods and rocker arms rubbed against these oil pads. The maintenance schedule called for the oil pads to be soaked in hot engine oil every 40 hours. So, massive amounts of lubrication was not considered necessary. I have a real rocker assembly recovered from a crash site, Even after 60 years exposure to all weathers, the push rods and rocker arms are spotless. They knew what they were doing.

For your 5 cylinder radial, keep persevering.  Make one component at a time and you will get there.

Stay safe

MIke
Title: Re: Bristol Mercury revisited
Post by: fumopuc on March 22, 2020, 10:58:36 AM
Hi Mike,
every time I have a look at this thread, seeing all these parts and machining set ups I am getting more and more speechless.
There is a lot of space to increase my model engineering activities and this space seems to get bigger and bigger every time.
Title: Re: Bristol Mercury revisited
Post by: MJM460 on March 22, 2020, 11:20:35 PM
Hi Mike, like others, I am continually amazed at the work you are doing on those engines.  Also your design ability to make it all come together and your tenacity to keep at the project for so long.

I don’t often comment, but when you see the number of reads increase after each post, you can be sure that I am one of them.

MJM460

Title: Re: Bristol Mercury revisited
Post by: Vixen on March 23, 2020, 10:39:55 AM
To all of you who called in, and to the many MEM members who are silently following. I know just how difficult it is to find the right words to reply. All I can think of to say to you all is

'Thank you all for your company on my long journey'

Stay safe

Mike
Title: Re: Bristol Mercury revisited
Post by: sco on March 23, 2020, 12:03:33 PM
To all of you who called in, and to the many MEM members who are silently following. I know just how difficult it is to find the right words to reply. All I can think of to say to you all is

'Thank you all for your company on my long journey'

Stay safe

Mike

 :ThumbsUp:
Title: Re: Bristol Mercury revisited
Post by: Vixen on March 25, 2020, 03:36:28 PM
I thought I would put something on the forum to give everyone something to look at during our enforced 'home' time.

The second Mercury is very close to completion. Here is one of the pair of magnetos mounted on the Accessories Drive Gearbox at the rear of the engine. You can see the nine plug leads running from this, the starboard magneto, to the right hand spark plug in each of the cylinders. Each cylinder is equipped with two spark plugs fired from separate magnetos for safety and reliability reasons. There will be more photos in the next, possibly the last, installment of this build.

The best definition of a 'reliable engine' I ever heard, is one you always have to switch off at the end of a long flight. Engines which switch themselves off and stop mid flight aint worth having.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080040small.JPG).atford


Somewhere along the way, I have lost the build photos of the magnetos. However, I did build six of them, two for each of the two engines. These four were configured only as distributors using external spark coils. The remaining two were intended to be used as spares or as the basis of self contained working magnetos, If I ever got that far.

From my box of spare parts I have been able to put together some recent photos of completed parts for the 1/4 scale Watford S.P. 9/6 Magnetos.

The first two photos shows a the main components. The little box under the distributor cap houses the ignition points, (actually Hall magnetic sensors on the model). Also shown is the input drive shaft for the separate ignition coil version. Note the offset horizontal key in the drive flange. This ensures the magnetos can only be installed with the correct ignition timing. The little pinion gear at the far end is part of the reduction gearing used to turn the distributor's rotor arm at the correct speed.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080032small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080036small.JPG)


Here you can see the fully machined main housing and the gear case.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080034small.JPG)


Here are the magneto coil cover and ignition point box

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080035small.JPG)

These parts are all machined from Delrin. They are the distributor cap, the rotor arm, the drive gear and the upper bearing housing.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080033small.JPG)


Along the way, at one of the London shows,  I met up with Jan Mulder from Holland. Jan had succeeded in making a fully self contained 1/4 scale magneto for his DH Gipsy engine. He was very keen to help me do the same for the Mercury engine and provided a complete (but damaged during manufacture) magneto coil, an endless selection of fine magneto wire together with lots of help advice and information.

The photos show one of Jans magneto coils posing in one of the Mercury magnetos. The coill is minute, it contains many thousands of turns of the finest insulated copper wire, all insulated layer by layer and vacuum encapsulated in epoxy. The coil's iron laminates would eventually sit on the two pole pieces either side of the rotating magneto magnets.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080026small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080028small.JPG)


Look at the attention to detail in Jans magneto coil. The little ceramic bead insulates the high voltage output where it feeds through the delrin gear and onto the rotor arm.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080029small.JPG)


Here are some of the wire reels provided by Jan. From left to right, the wire diameters are 0.035mm (13 thou), 0.028mm (11 thou) and 0.026mm (10 thou)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080038small.JPG)


I have yet to make a start on my working magnetos. First I would need to make a tiny coil wider and practice and practice. However I think I may have left it too late as this wire is thinner than an angles hair and very difficult (almost impossible) for these old eyes to see. :old:

Stay safe everyone.

Mike

Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on March 25, 2020, 10:58:56 PM
Another set of magnificent parts Mike   :praise2:

My first thought as I learned in my late childhood (when Dad flew Gliders) that you always do a "Power Run" with the wheel brakes fully on - before take off - where you start the run on both systems and listen for abnormal noises from the engine etc.
If all's good, you switch to only magneto I (without touching the Throttle) and listen again for a minute - if that's good - switch to magneto II and repeat + there should be not drop out or lower RPM's at anytime during this test ...!!!! .... so I couldn't thinking if your wonderful setup allows you to do the same ? (without the taking off happening  ;) ).

The next one was after seeing the copper wires - I have never seen an Ignition Coil that has tree different wire sizes / coils - so what is the idea here  :headscratch:

ps - in case you wonder why a glide pilot would know this - sometimes they used a "Tow Plane" to get in the air .... though the really mind blowing experience was to be pulled into the air with their big American V8 sitting with gearbox and all on the back off a big old lorry. It had one exit from the differential blocked and the wire drum bolted on instead off the wheel in the other. The wire went out through an highpower cutter that was spring loaded - and a wire went from that to the Emergency handle in the operators booth (with protection for the opperator) behind the wheelhouse - and the "power wire" continued out through a few rollers. One of those sets controlled the wire in the Horizontal plane and the other set in the Vertical plane.
The funny thing from a boys point of view when being allowed to watch things next to the operator was the original speedometer from the "Donor Car" was still attached the gearbox and the max speed that the wire was pulled in, was an indicated speed off 180Km/h ~ 112 Mph.
I haven't got a real clue about how much it translated into in real speed - but I can tell you how shocking it was first time I was in the Glider being pulled up that way. I had seen it many times and also helped with holding the wingtip up to horizontal and run along during start - but being onboard was a very different experience :
The wire is first very slowly pulled tight and the moment it is tight - the "wingman" lowers his raised arm and start to run the moment the operator hits the Throttle - until he (or she) feels that the Glider holds a steady wing position by itself and let go and the Glider gets airborne (this is only a distance of about 10 meters ~ 30 feet. The Glider now rotates to almost Vertical and the operator floors the Throttle.
Onboard this shocking as you suddenly has your back Horizontal and a few seconds later you are at about 3500 Feet up in the air. Not even Fighter Jets gets to that altitude so fast !!!!  (but they continue much higher and faster).
Title: Re: Bristol Mercury revisited
Post by: Vixen on March 26, 2020, 11:25:03 AM
Hello Per,
Your father taught you well. The preflight test you refer to is known as the 'Mag Drop Test'.

Two totally independent ignition systems have been mandatory for manned flight ever since the early days of flight and need to be tested before every take off. When you have large cylinders, 5.75" (146.0mm) in the case of the Mercury engine, the combustion flame front takes twice as long to ignite the charge when there is only one spark plug operating. This represents a drop in efficiency and the engine revs will drop. The pilots notes for running the Bristol Mercury say to slowly bring the engine to take-off boost (power) which is 2,500 RPM. With either magneto switched off the drop in RPM should not exceed 120 RPM.

The model cylinder is only 36mm diameter so I do not expect to see a Mag Drop like the full size engine, However it will confirm that both sides are working correctly. There are two ignition switches, one for each independent system.

The three wire sizes were a selection of different wires from which, hopefully, I could eventually wind the secondary coil for the magnetos

I love the story of you and your father at the glider field. Yes, those cable launches were pretty scary. A cable break at full power could send the glider into a nasty hammer head stall. You needed plenty of altitude to recover. I used to drive the Ferguson tractor all day at our local gliding club. My job was to return the tow wires from the winch to the launch point. In return, I would get to fly a glider back to the hanger in the evening.

Stay safe

Mike
Title: Re: Bristol Mercury revisited
Post by: Vixen on May 06, 2020, 12:02:10 PM
The second Bristol Mercury is now very near to completion. Just one or two small parts to make and fit.

The Mercury oil pumps are located at the back of the engine in the accessories gearbox. There are two spur gear oil pumps combined in one unit. The smaller displacement pressure pump feeds pressurised oil to the engines lubrication system, the used oil drains down to the sump and is removed by the larger capacity scavenge pump. The used oil is pumped back to the oil tank via an oil cooler.

Here you can see the oil pump assembly. The high pressure pump is within the bronze housing on the left and the scavenge pump is within the aluminium casing on the right

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080135small.JPG)


The scavenge pump housing will be a challenge to make and will require several different set ups and machines. I started with a length of 30mm diameter HE30 bar, long enough for the scavenge pump housing and a short sacrificial chucking length.  The six sides of the scavenge pump base flange were machined in the mill, indexing the stock in my 4th axis unit.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080054small.JPG)


The work was transferred to the lathe to turn the cylindrical parts of the pump housing. I used a parting tool with a 1mm radiused tip to do the profiling work. These parting tools will successfully cut sideways as well as plunge, provided the depth of cut is small.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080055small.JPG)


The embryo pump housing was transferred back to the mill to machine the two pump lobe cavities.  The pump cavities are formed below the larger diameter counterbore in sacrificial chucking length.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080057small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080056small.JPG)


The pump housing was inverted in the chuck and the external features were profiled with a combination of end mill and ball mill cutters.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080109small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080111small.JPG)


Next, The pump housing was transferred to a tilt table to machine the angled face for the inlet pipe connections. The inlet ports were then drilled and tapped.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080115small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080116small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080119small.JPG)


The final operation was to part off the sacrificial chucking piece and cleanup the rough edges of the scavenge pump housing.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080122small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080123small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080125small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080135small.JPG)


All that remains to do is to make up the 7 inlet/outlet pipe connections and blanking caps and give the scavenge housing a coat of paint.


Stay safe, keep your distance. :Director:

Mike
Title: Re: Bristol Mercury revisited
Post by: scc on May 06, 2020, 03:50:04 PM
 :popcorn: :popcorn: :LickLips: :praise2:    Terry
Title: Re: Bristol Mercury revisited
Post by: awake on May 06, 2020, 05:32:17 PM
Incredible, impressive work!
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 11, 2020, 02:04:38 PM
It's been a while since I updated this thread  on my two Bristol Mercury engines, so I thought you would like to see where I have got to.

Work on the combined pressure pump and scavenge pumps has continued. The housings have been cleaned up and all the inlet, outlet fittings, blanking caps and pressure relief valves have been completed and assembled.

The two larger pipe/hose fittings connect the scavenge pump to the oil sump and to the engine's main oil tank, via the oil coolers. The smaller connection dumps the oil from the pressure relief valves back to tank. This is to ensure the oil coolers are not over pressurised before the oil supply has reached working temperature.

The oil supply to and from the pressure pump section is through internal drillings inside  the Assessories Housing

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080501small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080502small.JPG)



Here you can see the exploded oil pumps mounted at the rear of the exploded Bristol Mercury display engine.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080507small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080506small.JPG)



Here you can see the gaping cavity in the side of the Accessories Housing (gear box) at the rear of the engine and again with the combined pressure and scavenge pump installed. It's getting rather crowded at the back of the engine.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080504small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080509small.JPG)



Building these two Bristol Mercury engines have been a very long journey which is nearing the end. I am not sure if I am pleased or disappointed now the end of the journey, the destination, is in sight.

Stay safe

Mike

Title: Re: Bristol Mercury revisited
Post by: steamer on November 11, 2020, 05:45:08 PM
As to how you should feel about it....

I think Steve spoke of a different topic but similar sentiment,... I think its apropos for you Mike.

https://www.youtube.com/watch?v=xvgpbsr-mCE
Title: Re: Bristol Mercury revisited
Post by: cnr6400 on November 11, 2020, 06:02:42 PM
 :ThumbsUp: :ThumbsUp: :ThumbsUp: :popcorn: :popcorn: :popcorn:

Top notch work Mike!   :cheers:
Title: Re: Bristol Mercury revisited
Post by: propforward on November 11, 2020, 11:37:17 PM
I know just how difficult it is to find the right words to reply.

"Inspirational" is the most appropriate I can offer I think. I get excited if I can turn a part to the right length within ±0.005", and hit diameters in the same way and get a good finish, so seeing something intricate like this kind of gives me a real boost as to what is possible through constant practice. I hit roadblocks a lot - scrapping parts, or things aren't going right, and seeing this kind of work just helps me keep going.

So  :ThumbsUp: :ThumbsUp: :ThumbsUp: to you, and I would say you have a lot to be pleased with on this project as you near completion. Thanks for taking us along.
Title: Re: Bristol Mercury revisited
Post by: Art K on November 12, 2020, 02:44:09 AM
Mike,
Great progress good to see you back at it and nearing completion. Most of my projects have been on hold, and with no shows on the horizon no need to push forward with them. I have some time off coming up so hopefully I can make some progress on them.
Art
Title: Re: Bristol Mercury revisited
Post by: Craig DeShong on November 12, 2020, 04:10:53 AM
Mike, your work is a constant inspiration.  I’ve thoroughly  enjoyed the journey.
Title: Re: Bristol Mercury revisited
Post by: Tonyr on November 12, 2020, 10:25:12 AM
I have been trying to think of a comment to add to this thread.
I can’t think of anything to say, it is that good.
Tony
Title: Re: Bristol Mercury revisited
Post by: Roger B on November 12, 2020, 10:58:34 AM
Excellent  :praise2:  :praise2:  :wine1:

Are you planning an alternative ignition system for the first trials?
Title: Re: Bristol Mercury revisited
Post by: Vixen on November 12, 2020, 11:33:48 AM
Thanks for all your kind comments guys and thank you to all those who are following along quietly in the background.  :ThumbsUp: :ThumbsUp: :ThumbsUp:

Roger, my thoughts are to use one of the magnetos as a distributor (centre terminal connected to the coil) rather than hope for a working 1/4 scale magneto. The magnets and Hall sensor are already built into the magneto units.

They started the full size engines in a similar way. The pilot hand cranked a starter magneto in the cockpit. this provided the sparks to fire the engine. The engine mounted magnetos only turned fast enough to produce sparks when the engine was running and up to speed.

Stay safe,

Mike
Title: Re: Bristol Mercury revisited
Post by: Vixen on January 08, 2021, 04:23:28 PM
Well, It's mid winter, nothing much is happening in the workshop at the moment and the forum is unusually quiet. I thought it may be a nice idea to give you all something to look at for a few minutes, something to take your minds off world events. So here is a repeat my slide show showing the completion of my two 1/4 scale Bristol Mercury radial engines. Work started on these two engines over twenty years ago. They have been a 'Work in Progress' for a very long time. I thought I would title this slide show

                                                                                               "Happiness is a lovely pair of Big Bristols"

Here you see the two completed engines side by side. One is an exploded display to allow you to view and examine both the outer and inner details of the Bristol Mercury engine. The second is fully assembled and almost ready to run

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080025small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080106small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080108small.JPG)


Lets start with a slide show tour around the exploded engine and then look at some of the details.

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080082small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080084small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080089small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080086small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080091small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080090small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080094small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080095small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080098small.JPG)



There is the second engine. It has now been fully assembled and almost ready to run. It will need a 36" diameter propeller before that can happen. As before, I start with a tour around the outside before looking in on some of the details.

(https://listerengine.com/coppermine/albums/userpics/10013/P1080016small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080015small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080009small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080011small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080017small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080068small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080069small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080019small.JPG)

(https://lister-engine.com/coppermine/albums/userpics/10013/P1080005small.JPG)



 
I hope you liked my slide show. Apologies if some of you may have seen it before, but it did go some way to filling an otherwise cold and dull winters day



Mike
Title: Re: Bristol Mercury revisited
Post by: cnr6400 on January 08, 2021, 05:18:09 PM
Great photos! have seen some of them before and they are always a treat. Outstanding work.  :ThumbsUp: :ThumbsUp: :ThumbsUp:

Liked the "big bristols" philosophy. Been a good plan for me since high school!   :Lol:   Oh wait, this is an engine thread........ :Lol:
Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on January 08, 2021, 07:33:11 PM
Quite a good number of engines build on this site will always be nice to see again  :)
Though it's different tastes between us all here, we do also have a lot in common taste vices .....
In my case as a petrol head and some interest in flying and planes - this one certainly 'Floats my Boat'  :cheers:
Title: Re: Bristol Mercury revisited
Post by: fumopuc on January 09, 2021, 10:39:29 AM
Speechless.

Title: Re: Bristol Mercury revisited
Post by: Vixen on January 09, 2021, 10:42:35 AM
Thank you both,

Per, the truth is, so much has changed over the last year. The fine toys we used to build have lost their importance, lost any relevance. They now belong to a previous world.

The previous post was my way to mark the end of a long journey. I have finally reached that destination. And I have enjoyed the company of all of you along the way

Take care

Mike
Title: Re: Bristol Mercury revisited
Post by: propforward on January 09, 2021, 12:20:54 PM
Fantastic work. I can revisit those engines again and again.

I think coming together to share these is even more important now than ever.

Inspiring builds as always, thanks for brightening my day!
Title: Re: Bristol Mercury revisited
Post by: Trevorc on January 09, 2021, 02:39:21 PM
Mind blowing! Very envious of your abilities.
Thanks
Trevorc
Title: Re: Bristol Mercury revisited
Post by: petertha on January 09, 2021, 04:35:28 PM
Thanks for posting Mike. Every time I look at these engines I see another level of detail I missed the time before. Very impressive accomplishment!
Title: Re: Bristol Mercury revisited
Post by: Kim on January 09, 2021, 05:28:39 PM
Just amazing!  You have done incredible work here!  Those engines are gorgeous!  And I love how you did the exploded view.  Just incredible!
Kim
Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on January 09, 2021, 08:20:38 PM
Quote
Per, the truth is, so much has changed over the last year. The fine toys we used to build have lost their importance, lost any relevance. They now belong to a previous world.

The previous post was my way to mark the end of a long journey. I have finally reached that destination. And I have enjoyed the company of all of you along the way

Was this meant as a goodbye Mike ?
If this is the case, I for one will miss your company and say thank you for your great contributions here.
If it on the other hand is a kind of I'm beyond caring until this Covid thing has come to and end - I hope you find a number of good books etc. or whatever can keep you out of trouble ....

Best wishes

Per
Title: Re: Bristol Mercury revisited
Post by: Vixen on January 09, 2021, 10:30:35 PM
Was this meant as a goodbye Mike ?
If this is the case, I for one will miss your company and say thank you for your great contributions here.
If it on the other hand is a kind of I'm beyond caring until this Covid thing has come to and end - I hope you find a number of good books etc. or whatever can keep you out of trouble ....

Best wishes

Per


Per,
No it's not a goodbye.

It's a change in perspective and priorities. My wife and I have been, like so many others, confined to the house for the last 10 months.  Spending endless hours alone in the workshop building engines, no longer seems as important as time together.

Best wishes to you, Stay safe

Mike
Title: Re: Bristol Mercury revisited
Post by: nj111 on January 11, 2021, 01:26:34 PM
As others have said that is incredible work Mike!
Also, I'd like to take this opportunity to thank you for your enormous input here over the years.  In addition to your super human practical abilities you are a mine of accurate information and advice for us all! 
For those like myself it's hugely inspiring to see how you have created your complex builds. I really enjoy your posts.
Will the little Westbury 4 cyl build continue in due course?
Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on January 11, 2021, 10:49:06 PM
No problem Mike.

I have been working at work for the duration, with a total 14 days of holiday - so my reality has been completely different from a good number of other members here.
But I do have not problem with the need for a change of direction (though the options are somewhat limited in these times) ....

What ever you decide to spend your time on Mike - I hope you enjoy it  :cheers:
Title: Re: Bristol Mercury revisited
Post by: AVTUR on January 12, 2021, 03:31:30 PM
Mike

Good luck with your future ventures and I hope you continue with the Seal.

Maybe we will meet at RRHT.

AVTUR
Title: Re: Bristol Mercury revisited
Post by: Vixen on January 12, 2021, 06:19:09 PM
Hello AVTUR

I believe Per may have got hold of the wrong end of the stick. I am not about to say goodbye, I am not about to disappear. My intention was only to cut back on the time spent in the workshop each day. I plan to continue to contribute to this excellent forum from time to time. And when conditions permit to return to the model exhibition scene with renewed energy.

Do you remember that caption on the television, when we were youngsters,     

"Normal service will be resumed as soon as possible"

In the meantime, I still have lots of modeling work ahead of me. The update program on the two Bristol Mercury engines has be completed

That still leaves the Bristol Jupiter     http://www.modelenginemaker.com/index.php/topic,7559.0.html

The Mercedes Benz W165      http://www.modelenginemaker.com/index.php/topic,5142.0.html

And the Westbury Seal     http://www.modelenginemaker.com/index.php/topic,9709.0.html

All are waiting to be progressed. The Westbury Seal is very near to completion.

Stay in and stay safe

Mike    strictly AVGAS
Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on January 12, 2021, 08:39:42 PM
To be honest Mike - the way I read your original post, I thought that it could be understood in more than one way and I simply wanted to be sure that if the meaning was about leaving - I would make sure I expressed my gratitude ..... and if not - I felt that you would point out my error  :old:

Per
Title: Re: Bristol Mercury revisited
Post by: petertha on July 27, 2023, 08:08:00 PM
Work on the combined pressure pump and scavenge pumps has continued. The housings have been cleaned up and all the inlet, outlet fittings, blanking caps and pressure relief valves have been completed and assembled. Mike

Mike, I know this is an older post & you have lots of other interesting projects on the go. But did you ever bench run your oil pump system? If not, no problem. I'm curious if the key dimensions were more influenced by scaling the actual engine pumps or if you also tweaked with model specific design parameters? Any rough idea of delivery pressure, flow rate, gear dimensions, RPM etc.
Title: Re: Bristol Mercury revisited
Post by: Vixen on July 27, 2023, 09:57:05 PM
Hello petertha,

The oil pressure and scavenge pumps for the Bristol Mercury engine are (nearly) exact copies of the full size oil pumps, hence appear to be more complex than necessary. I'm a slave to scale.

A scavenge pump should have 1.5 to two times the capacity of the pressure pump that supplies the oil to the engine.

Pinion pumps are constant displacement pumps. The amount of oil pumped is therefore dependant on the size of the gear teeth, the number of teeth in the two gears and the rotational speed. True, you will get some leakage over the ends of the teeth so keep the clearances as small as possible. The pinions in the Bristol Mercury pumps are made from 0.8 MOD gears 0.375" (9.5mm) diameter. They rotate a about 7/8 crankshaft speed. it's always good to keep the pump speed as low as possible.

There seems little risk of cavitation at model engine sizes as the pumps are small with comparatively low flow rates.

Output pressure depends on the load. An open ended pipe, feeding ball races, will see very little output pressure, whereas a plain bearing, which restricts oil flow, will increase the pump pressure. The pump pressure is therefore dependant on the restriction placed on it's output. You will be surprised how little oil is require to lube the bearings, remember most two stoke engines are lubricated only by a tiny quantity of oil mixed in with the fuel.

Most full size aero engines and racing engines rely on excess lube oil flow to help cool the internals of the engine, thereby reducing the size and drag of the coolant radiators. Not normally an issue with model engines.

Cheers

Mike
Title: Re: Bristol Mercury revisited
Post by: petertha on July 30, 2023, 12:36:30 AM
Thanks for the info Mike, very helpful. I was wondering if you had bench run the pump or had a rough idea of numbers by your own design because behind the scenes I was busy plagiarizing & bastardizing & metrifying David's pump spreadsheet for my own selfish purposes. I have been thinking about purchasing metric gears in the similar sub-1.0 module range to build an evaluation pump. Even with small gear diameter & reduced module they appear to kick out a lot of fluid. So much so that I was suspect I messed up the math or something else going on. Your gear width is longer yet (you mentioned scale) so I thought that would be particularly useful info if you filled a X liter bucket in Y minutes. Probably this 'pump design' discussion best belongs in the other more general gear pump post. I didn't want to clog up your build post, so I'll leave that to you. But for interest sake, just eyeballing the gear width & guessing at some other parameters, I get numbers like this. Does it seem sane to you? Happy to share the spreadsheet, particularly if you see a bust.
Title: Re: Bristol Mercury revisited
Post by: steamer on July 30, 2023, 03:11:35 AM
Peter,

Just a note.    The pressure in my spreadsheet was an INPUT.    I wanted 10 psi available in my pump, and I wanted to know how much power that would consume at that pressure.   The  actual pressure in YOUR system will depend on the down stream plumbing/orifices/restrictions/viscosity/

I am going to balance my fixed flow nozzles to an appropriate flow rate at probably 10 psi....plus or minus a bunch.   Again, what it takes to make it work will not be very much IMHO, so it's a balancing act that I'll need to sort out on the bench, and not a closed form solution.....but the spreadsheet gives you some idea of where your at as a starting point.....

Now what is an appropriate flow rate for a bearing!?   That's a great question!   How much will my system need?    Also a great question!  and one I've been asking myself for some time!


To answer this, I sat an thought about this for sometime?  and I finally decided to perform this thought experiment.

I asked myself, if this bearing was open, and running on the bench, as I stood over it with an oil can, how much oil would I give it as it was running at 8000 rpm?  

Remember now, this is a bronze bearing on a hardened A2 tool steel shaft, quite polished and good fitting.   Method of application is basically splash lubrication with a boundry layer lubrication. meaning it's hydrodynamic.   
The purpose of lubrication is to reduce friction and wear and carry heat away from the bearing.    OK.   

Wow...not very scientific I know.    Guilty, but splash lubrication is by definition not very scientific.....

Furthermore....remember that the 4 stroke model airplane engines on the market lubricate with nothing but adding oil to the fuel and count on some blow by to lubricate the VERY simple bearings, ....so how much oil is transferred to the bottom end of one of these engines?    NOT A LOT!

So rational me decided I would lubricate this bearing on the bench at 1 drop every 2-3 seconds.   I call this the rational man approach.....  Not scientific, but....

How much oil is in a drop of oil?    Google tells me 0.064 milliliters.
How many bearings am I feeding in this engine?     6 double throws and a gear train ( I am assuming the same flow to the gear train)

1 drop/3 seconds x 7 is works out to 140 drops per minute... 

140 x 0.064 milliliters is 9 milliliters/minute    That is going to be a very small pump!!!!!

Too small!!     These pumps are pretty fussy to make and function well, lots of concentric features that need to line up ect, and small gears are pretty fragile.

My pump, which is about as small a pump as I think I can make reliably.    It is capable,   theoretically to 560 milliliters a minute!!!   Or about 62 times the minimum amount of oil I think I need.... an that is the rub.     I think the pumps we can reliably make are going to be big compared to what we need!

My pumps are 48 DP which is equivalent to 0.529 MOD.    Small!

I also looked at Ron Colonna's Offy plans which if IIRC, is also a 48 DP pump and runs at 1/3 engine speed  ( I'm running faster at 1/2 engine speed)  and got a similar size oil and scavenge pump, and he has silver bearing mains on 4150 steel crank, with drilled crank oil passages.   I have ball bearing mains and bronze bearings running on hardened steel crank pins....which is a great bearing pair.    I'll dig up the build book and quote chapter and verse, but it's a similar size to mine, and it's slightly larger engine displacement IIRC.

so now for me,  the next step is to test with my preferred oil spray bar which will have 7 nozzles aimed at the components i've mentioned.    I'm going to start with a 0.005" hole as a nozzle and 10 psi....ish    but I think I have plenty of leeway here.....I don't think I need very much and I think most of the oil will be cycling back to the oil tank.

Dave






Title: Re: Bristol Mercury revisited
Post by: Vixen on July 30, 2023, 10:51:17 AM
Hello petertha.

Thank you for your interest in the Bristol Mercury oil pumps and for this lively discussion. I will create a new topic on oil pump design and move this discussion there, so it will be easier for other to reference it later. Leave that to me to do, in the mean time keep posting here.

No, I have not built a flow test rig to measure the flow rate of the pressure and scavenge pumps for the Mercury engine. I am sure the flow rate is amenable to calculation. I have looked at the gear displacement calculation in your spreadsheet and cannot come to terms with it. Your calculated pump flow rate of 2,099 ml/min ( 2 litres/min) at 2000RPM looks to me to be rather optimistic

The oil being pumped is entrained in the gaps between the teeth of the two gears. I would therefore have expected your displacement calculation to have considered both the outside diameter and the depth of the gear teeth, multiplied by an estimate the the tooth to gap fill ratio and the number of active gaps surrounding the two gears.

The pressure pump gears for the 1/4 scale Mercury engine are 9.6mm OD and 9.6mm wide, 0.8 MOD.

As for the required flow rate, most agree that only a small proportion of the flow is used to lubricate the bearings, the majority of the flow is used to cool the inside of the engine. Internal engine cooling is particularly important with air cooled engines, like the Porsche 917 and most radial aircraft engines. The oil flow rate of a full size oil pump will therefore be determined by the engine's worst case operating conditions i.e. take off (or racing) in hot, high altitude, desert conditions. Fortunately, we only need to consider running our model engine in our back yard conditions.

Mike
Title: Re: Bristol Mercury revisited
Post by: steamer on July 30, 2023, 11:38:32 AM
Peter's reference was from my spreadsheet Mike, as is the volume approximation formula.    Spreadsheet errors aside, which I have not looked at Peter's yet.

As far as cooling, absolutely, lubrication is a lot of cooling for sure.    That said, most model airplane 4 strokes are air cooled and function well with nothing but oil in the fuel/blowby.   These models don't put out the amount of heat that the full size does  ( cube root of size and all)

Dave
Title: Re: Bristol Mercury revisited
Post by: John Roberts on July 31, 2023, 04:17:29 PM
Mike, I have only been following the forum builds since I started making the Triumph t100 engine. I am totally blown away at the detail that you have put into this engine. I thought I had patience but for you to make two engines, unbelievable. Drawing an engine in 2d can be difficult to spot errors as you know. Your ability to make do with what you have got is commendable.
 It must be difficult to have milled the larger parts with such a small  X , Y axis envelope on your mill.
 I do have 3d modelling skills and have 3d cam. I know little about g code and would not know where to start adapting code to cut the complex parts you make. Thankfully I don't have to.
I have not decided what my next project will be, but I am going to have to up my game to come close to what you produce!
Like you and others, I have em-braised CNC machining and the challenges it brings.

John.
Title: Re: Bristol Mercury revisited
Post by: Vixen on July 31, 2023, 05:48:51 PM
Thank you John,

Like Cortés, when he discovered the new world; I burned my boats as well; so CNC was the only way forward. The only handwheels I have in my shop are the tailstock handwheels on the two lathes. Everything else is done by the numbers(CNC). I have been using the same CAD package and much the same CAM software for more than 20 years and feel I am at last getting the most from it.

That's what they call experience. And as we all know, experience is that which allows us to make the same silly mistakes every time .... but with total confidence.  :facepalm:

Mike
Title: Re: Bristol Mercury revisited
Post by: Admiral_dk on July 31, 2023, 10:07:56 PM
Quote
That's what they call experience. And as we all know, experience is that which allows us to make the same silly mistakes every time .... but with total confidence.  :facepalm:

I know that one FAR to Well  :facepalm:  + it doesn't only apply to CNC  :wallbang:

Per   :cheers:
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