Author Topic: Burrell Single Crank Compound Traction Engines - 4" Scale  (Read 43148 times)

Online Jo

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #75 on: August 06, 2016, 01:33:30 PM »
This is what Tgs has set up above his head. The wheels allow for sufficient movement to take Tgs heads or castings clear of the front of the bed and down onto the roller skate to move them off to their storage location.

My supplier has the advantage of rafters so he just hangs his off a length of scaf poles which span 4 joist.

Jo
« Last Edit: August 18, 2017, 11:00:43 AM by Jo »
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Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #76 on: August 08, 2016, 11:22:45 AM »
Andrew as you have no floor space for a crane think about an overhead beam with a beam trolly or a swing out arm for a "barrow hoist" located near the lathe and one gor the mill. I assume you have a bit of wall or ceiling space but that could be wishful thinking on my part :-\

Almost no wall space, and not much ceiling space! I am planning a double rail attached to the ceiling joists that will allow me to run a manual hoist. The intention is to cover the centre lathe and all three milling machines, as they're the machines that have the heaviest accessories. I'll probably include some support pillars, as the joists are not that large.

Some while ago I had a look at the 'crane' that John Stevenson added to his Bridgeport. If extended it could cover all the machines, but would be a PITA when I wanted to swivel the Bridgeport ram, as I have operational heads on both ends.

Andrew

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #77 on: August 20, 2016, 11:11:26 PM »
The final drive gears are the last gears to be made for the engines, apart from the governor bevel gears, which are designed but not yet machined. As is the norm with me the final drive gears have been a bit of a drawn out saga. I started machining the castings some years ago. The OD is 14.8" so they were bolted onto the large faceplate:



After machining the first casting I discovered I had some runout, up to 20 thou, on the OD, side to side, radially it was fine. :embarassed: At this point I gave up and moved onto summat else. After I had machined the flywheel some while later it sank in that I must have distorted the casting when bolting it down to the faceplate. So I changed the way I clamped, and drove, the castings and then carried on regardless (English joke):



After tidying up the part machined casting and machining the remainder the maximum runout was 4 thou or less - much more acceptable. One needs to keep in mind that on the full size engines these gears were often 'as cast', gear teeth and all. There was no way no how I could get the gear blanks on the dividing head and under the arbor/cutter on the horizontal mill in the normal manner. I considered 'overcutting' where the gear sits above the arbor and cutter, with the outboard end of the arbor supported by a special support down to the mill knee. However, this wouild have required a considerable amount of hardware to be made, not least some large riser blocks for the dividing head. So in the end sense prevailed and I decided to cut the gears horizontally, using the rotary table rather than the dividing head:



Fortunately the gears have 72 teeth so each index is exactly 5, making the indexing easier. Note the spotlight in the picture shining on the rotary table scale. A disadvantage of the method is that the mill table and knee need to be raised and lowered, by hand, to cut each tooth. I found I could do about a third of a gear at a time before needing tea. It keeps yer fit if nothing else. The teeth are cut full depth in one pass, and although not obvious there is support under the casting near the cutter. Here are the four final drive gears, and winding drums:



I actually cut the teeth on six gears, as my mate just 'happened' to have his gear blanks machined and ready at the same time.  ;)

Andrew

« Last Edit: August 17, 2017, 10:37:21 PM by jadge »

Online crueby

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #78 on: August 20, 2016, 11:46:00 PM »
Very nice! Those gears are beautiful monsters! Bet you could build a nice tower clock movement...

 :popcorn:

Online Kim

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #79 on: August 21, 2016, 12:52:50 AM »
Your gears look great, Andrew!  Cutting six 72 tooth gears of that size, by raising and lowering the knee, that's a lot of work!  You must be exhausted!

I'm doing some gears right now too, but they are MUCH smaller :)

Kim

Online Jo

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #80 on: August 21, 2016, 07:47:02 AM »
A disadvantage of the method is that the mill table and knee need to be raised and lowered, by hand, to cut each tooth. I found I could do about a third of a gear at a time before needing tea. It keeps yer fit if nothing else.

 :Lol: Yes I found with "H" winding the knee up and down makes my arm ache after a while. Which is why when I went looking for my "bigger mill" to make my Steam Plough on I made sure it came with a powered knee  :cartwheel:

I'll have to be careful of these friends just happening to have gears ready for cutting as I get to that stage. I can see someone wanting to visit to have his winding drum gear cut. Assuming he has worked out how to turn it on his Chinese lathe by then :mischief:

Jo
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Offline scc

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #81 on: August 21, 2016, 09:37:38 AM »
Nice work Andrew      :ThumbsUp:                Terry

Offline Steamer5

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #82 on: August 21, 2016, 02:11:29 PM »
Hi Andrew,
 I got worn out just thinking about how much handle winding you had to do to cut those gears! Well done! Who needs to waste time at the gym when you have a project like this on!

Oh by the way just watched Carry on up the Khyber, they are playing one a week, I'd forgotten how funny there are! (Must be my bent sense of humour!)

Cheers Kerrin
Get excited and make something!

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #83 on: August 23, 2016, 08:47:25 PM »
Thanks for the kind words. The answer is 432 cycles, plus a few to check that the cutter passed cleanly through the first gap cut, so as to double check the indexing. Just listening to the noise, or lack of it, my impression is that the rotary table is tad more precise than the dividing head after going round once.

It's good that a least one person got the joke. Some of the Carry On films have dated a bit, but 'Carry on up the Kyhber' is still well worth watching. Of course one wouldn't be allowed to make such films these days.  ::)

Andrew

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #84 on: September 03, 2016, 11:25:32 PM »
I have previously shown shown a picture of the hollow pistons for my traction engines, but I hope I haven't described them before in this thread, or I'm going to look a right Rodney.

Full size engines had hollow cast pistons to save weight thus reducing the reciprocating forces on the connecting rod, bearings and crankshaft. In 4" scale the norm is to use aluminium pistons rather than cast iron to save weight. However, aluminium has a larger coefficient of thermal expansion than cast iron. To allow for this the piston is made undersize, if I recall correctly the allowance is 4 thou per inch of cylinder diameter. For my LP piston which is ~3" diameter that is 12 thou, otherwise known as a rattling good fit. I wondered if it would be possible to make hollow cast iron pistons, as two halves screwed together. Some playing in 3D CAD showed it was possible. The hollow cast iron HP piston would weigh about the same as the solid aluminium piston, but the hollow LP piston would be somewhat lighter. Here is a section of the two parts of the LP piston:



It seems sensible to check and see whether the hollow pistons would survive the boiler pressure. Now of course in reality the pressure in the cylinder is going to be lower than boiler pressure due to losses in the passages and possibly wire drawing in the ports. However, I chose to use full boiler pressure (170psi) for both cylinders. That may seem strange for a compound, but I am planning to fit a simpling valve, as per full size, which allows boiler pressure steam to be applied to both HP and LP cylinders for extra ooomph. For the LP piston here are the deflections under 170psi, derived from a FEA add-on package to my 3D CAD:



And here are the stresses, all comfortably below the strength of the cast iron (GR17). Note that the central boss is filleted, this is to reduce the stresses due to a sharp change of section:



Having modelled the pistons it seemed sensible to 3D print them to get a look and feel. Note that these were printed before I altered the boss of the LP piston to a fillet (piston top left):



Turning the piston halves is straightforward, if a little tedious. Here are all the tools used for both halves:



This picture shows cutting the thread that holds the two halves of each piston together. Since my lathe is imperial I chose to use a Whitworth form 32tpi thread. After cutting reliefs there are about three pitches on the thread. The internal thread halves were made first, and these were used a gauge to check the external threads. Before each fitting care was taken to brush the thread with a fine brush to remove cast iron dust, otherwise one gets a false impression of the fit:



The final operation on each half was to nearly part off, the final cut being made with a hacksaw. The piston ring grooves are exactly to width and depth for the Clupet piston rings I have decided to use. However, the OD of the pistons are left approximately 15 thou oversize. The completed pistons will be ground to final size once I have made and fitted the liners:



Once the halves of the pistons are made they can be screwed together and mounted on an expanding mandrel in the collet chuck to bring the piston to the correct width and to machine the recess for the piston rod nut. Hollowing out the internals of the pistons and forming the ribs was a simple operation on the CNC mill. A 6mm cutter was used for bulk material removal and a 4mm cutter for forming the ribs:



Finally here are the finished piston halves, piston rods and nuts:



The piston rods and nuts are made from 303 stainless steel. My experience of 303 stainless is that it is easy -peasy, and that was true for the nuts, simple to get an excellent finish. The opposite was true for the rods, they turned like a complete pig. So much so that I went back and checked my invoice from the commercial steel stockist to make sure I'd got the right material. You never know with commercial metal stockists. As well as the traction engine material I buy quite a lot of metal and plastic for work. I can safely say that commercial metal stockists are hopeless. I've had the wrong size delivered, metric when I've ordered imperial, and vice versa. I'm always amazed when the complete order is actually on the lorry all at the same time. And on the last aluminium order they missed off a 6 metre length of angle. When it was delivered the next day it resembled a banana having a bad day. I took it anyway, but insisted on a credit note.

Back to the 303 stainless; after some experimentation I found that slowish sfm, with coolant, gave an acceptable, but not great. finish. Oddly enough screwcutting the 32tpi thread was absolutely no problem.

Of course, when the engines are finally assembled all this work will be lost to the outside world, but at least I will know what is there internally.

Andrew

Rodney = plonker - from the UK TV show 'Only Fools and Horses'
« Last Edit: August 17, 2017, 10:43:46 PM by jadge »

Offline Steamer5

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #85 on: September 03, 2016, 11:37:41 PM »
Hi Andrew,
 Oh goody, saw you article in M.E.(well I think it was yours) on making these, now will have to digest this.
No popcorn today, it's farther day here, so I requested Eccles cakes  : :P!  And they have just come out of the oven, so time for coffee too!

Cheers Kerrin
Get excited and make something!

Online crueby

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #86 on: September 03, 2016, 11:46:12 PM »
I've never seen hollow pistons before - thanks for the details, and great work!!

Offline fumopuc

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #87 on: September 04, 2016, 06:51:48 AM »
Hi Andrew, very interesting piston project. Impressive how you did the entire process, like in real job live.
Kind Regards
Achim

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #88 on: September 04, 2016, 10:27:56 AM »
Oh goody, saw you article in M.E.(well I think it was yours) on making these, now will have to digest this.

Correct, it was my article in Model Engineer, a couple of years ago if I remember correctly. I'm now in the process of writing up the design and manufacture of the water pump for ME.

Ah, Eccles cakes, mmmmm. It hadn't occurred to me to heat them? I'll have to try that next time I buy some.

Andrew

Offline Steamer5

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #89 on: September 04, 2016, 11:02:39 AM »
Hi Andrew,
 At the time the Eccles cake were fresh out of the oven! Raewyns a very good cook!

It's going to be interesting to see how they preform, the reduced weight has got to be good & similar materials for the cylinder & piston can't be bad!

Cheers Kerrin
Get excited and make something!