Author Topic: Burrell Single Crank Compound Traction Engines - 4" Scale  (Read 35678 times)

Offline deltatango

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #150 on: June 20, 2018, 12:09:36 AM »
Andrew,
It's good to see progress on the two engines. Not having much room to spare in the workshop must also be a problem for moving heavy objects around. I've learnt a lot about riveting for your posts - thanks!
Regards, David

Online Kim

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #151 on: June 20, 2018, 06:34:18 AM »
Nice rivet work on your wheels, Andrew!  Looks like your rivet jig worked quite well!
Kim

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #152 on: June 26, 2018, 03:37:27 PM »
It's good to see progress on the two engines. Not having much room to spare in the workshop must also be a problem for moving heavy objects around. I've learnt a lot about riveting for your posts - thanks!
At least one can roll the wheels for most of the distances needed. Lifting them onto the mill/flypress is more of an effort though. I'm glad you've gained something from my trials and tribulations.

Andrew

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #153 on: August 11, 2018, 10:01:44 PM »
While working on the front end of the traction engines I thought I'd have a go at the smokebox door and nameplates. These are supplied as castings:



Turning the back of the smokebox door, and creating a register to allow the door to be held front face out, is simple:



When turned round the OD can be brought to size. To machine the front face requires a large radius to be turned, 18" in this case. Normally I'd fudge it with some angled cuts, files and emery. But the nameplates need to fit neatly on the front face so I need a means of creating an accurate radius, and a matching radius on the underside of the larger nameplate. I have a hydraulic copying unit and while these are nornally used for profiling parts parallel to the lathe axis there is no reason why they cannot be used for facing. Accessories were available for this, but it seems to have been quite a rare operation, and there is very little information on the internet. Generally my lathe already has mounting holes and brackets for 3rd party accessories, like the copying unit. But there is nothing on the saddle to hold a bar that then holds the template for facing. So I came up with a simple clamp arrangement, and hogged a profiling bar out of a lump of hot rolled steel:



For those interested in scale the bar is 20" long. I was keen to get the bar made so I ran the Bridgeport hard, in a subdued light the swarf was coming off red hot and didn't half hurt if you got hit by it. When roughing out the rebates with a 10mm endmill I used a DOC of 5mm, WOC of 7.5mm and a feedrate of 300mm/minute at 2000rpm. The force needed to turn the table handle in the climb milling direction was significantly lower that for conventional milling. So that's what I did, climb milled.

A simple sheet metal template was hand cut from sheet, and the curve machined on the CNC mill, less than 3 minutes machining time! Here's the setup in action machining the front of the smokebox door. I had some issues with surface finish and found that feeding from the outside to the centre worked best. Which, if I'd thought about it, gives a better cutting geometry for the profiling insert:



Profiling the back of the outer nameplate is similar, using a second template. The door and nameplates fit together snuggly with no rocking:



I'm not overly happy with the lettering on the nameplates. The outer nameplate can be tidied up with a small chisel and files. But the inner nameplate has lost significant resolution as there is a large draft on the letters and the depth of the recess is not constant. So when the front is skimmed the letters come out different widths. Of course I could ignore it and just thump any rivet counters that pointed it out. But I'm inclined to bin the casting, update the 3D CAD model and create the lettering on the CNC mill.

Andrew

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #154 on: August 19, 2018, 11:24:42 AM »
The perch brackets are now fitted to the smokeboxes. I first tried drilling by hand, but that proved to be a fudge too far. So I reverted to using the milling machine:



The smokebox is clamped to an angle plate and an angle of dangle meter used to set the drilled surface of the casting roughly horizontal. Top middle right the small protrusion from the perch bracket is a bar with a small spigot on the end. The spigot engages with a hole in the smokebox to help alignment. Afterwards the hole is tapped and a screw fitted. I can then remove the screw and use the hole to oil the bracket that holds the front axle. To align the drill with the existing holes in the casting I used my ears. You can hear a 2-flute catching the edge of the hole when the quill is lowered. As the table is moved this changes to a swish as the drill enters the hole cleanly. Doing this in X and Y is quite quick and achieves an accuracy that is acceptable in this application. I spotted the smokebox using a 1/4" drill followed by a tapping drill for 1/4" BSF. Before moving clamps the holes were partially tapped to ensure alignment. Final tapping was done afterwards with the perch bracket removed. Here's the final assembly:



The homemade studs were individually adjusted to allow for varying casting thicknesses so that the same number of threads show above each nut. I couldn't find a new 1/4" BSF die (probably didn't buy one as I use a Coventry diehead for making the studs) so I used an old one marked AM (Air Ministry) and 1940. No doubt it is carbon steel, and had a chip or two, but it still worked fine.

Andrew

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #155 on: August 26, 2018, 11:38:07 PM »
But I'm inclined to bin the casting, update the 3D CAD model and create the lettering on the CNC mill.

Which is what I did! I spent ages creating a CAD model and generating CAM files. Then someone on another forum kindly sent me detailed pictures of the front end of a full size SCC engine. Which showed that my lettering and size was completely wrong, so I binned all my CAD and CAM files. However, I simply couldn't get all the proper lettering to fit. Then I noticed that the font on the full size engine is very narrow, it looks quite odd. So presumably the original pattern makers had the same problem. I didn't have access to a narrow enough font, but by creating individual parts for each letter I was able to scale each letter in width only. And then I could create an assembly with the correct width lettering. I had some real problems getting the assembly into the CAM program. My CAD program won't generate IGES files from an assembly, and my CAM program gets scaling wrong with STEP files. In the end I called the UK agent for my CAD program and their technical guru ran me through a procedure to convert an assembly into a single non-editable part. But not before I'd lost all my work when the CAD program overwrote everything.  :(

Today I've been playing with the final tweaks to the CAD and CAM and running the CNC mill. Here's the prototype nameplate ring in a piece of scrap alumimium from a client project:



I spent quite a while thinking about fixtures and turning the ring concentric with the CNC milled lettering. But by CNCing the inner and outer circles on the ring the fixture for the final rings in brass was very simple:



And the final two rings in CZ120, engraving brass:



The thickness at the bottom of the circles varies from 0.15mm to zero, so I should be able to break out the rings fairly easily. All milling was done with a 1mm cutter running at 350mm/min and 24000rpm with a step down of 0.2mm per step. The depth of the engraving is 0.635mm (25 thou). Machining time per ring was about 1 hour 20 minutes.

Next job is to machine the central cast iron boss in which the brass rings are embedded, as per this CAD assembly:



Andrew

Offline zeeprogrammer

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #156 on: August 26, 2018, 11:43:33 PM »
They look great!  :ThumbsUp:

It does make one think about CNC.
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
"To work. To work."
Zee-Another Thread Trasher.

Online Kim

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #157 on: August 27, 2018, 05:13:18 AM »
Andrew,
That was a lot of work but the finished product certainly makes it all look worth while!
Kim

Offline deltatango

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #158 on: August 27, 2018, 06:28:25 AM »
That was a big effort Andrew! Was Alibre playing up? One hour 20 sounds quick to me.

Regards, David

Offline Jasonb

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #159 on: August 27, 2018, 07:21:34 AM »
They look good Andrew, should be even nicer with some red paint flowed in to cover the tool marks which should show off the lettering even more.

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #160 on: August 27, 2018, 10:01:34 AM »
Thanks for the kind words. I had some issues with Alibre, primarily when converting an assembly to a part. The first time I did it all my files got overwritten with non-editable versions. After talking to the UK distributor I clicked the tickbox that said save the part file to a separate location. Simple, but not obvious when you don't know. The lettering is rather better than on the full size engine! But of course the original builders didn't have CNC available.  ;D

Given that the smokebox is going to get hot I'll probably paint both inner and outer nameplates with the same high temperature black paint that I use for the smokebox proper. That seems to be in accordance with the pictures I've been sent of a full size engine. Although it's difficult to tell what's paint and what's grime!

I'm itching to start machining the central boss, but I have to go out soon to do an aircraft inspection. Followed by a stint as afternoon tug pilot. It's going to be quiet looking at the weather; flyable but not really soarable.

Andrew

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #161 on: August 31, 2018, 09:28:13 PM »
The central bosses are now made:



Actually I made three due to a foul up on the dimension of the inner diameter of the groove on the second one. I made a thin steel ring and loctited it in place to compensate. But I wasn't very happy with it, especially as the smokebox will be getting hot, so I made another one. Fortunately I didn't have to buy more material. The lengths of cast iron I have for the cylinder liners are longer than the liners as it assumed the pistons are cut from them. Since I made my own pistons to a home brew design I had metal to spare. The HP liner was just right. The groove for the nameplate ring is very slightly (a couple of thou) oversize. The last thing I want to do is push the ring into place, and not be able to get it out again!

I'm now getting niggled by the dots around the word BURRELL on the outername plate instead of proper quote marks. I'm thinking of CNCing some quotes and somehow fixing them in place of the dots. Sadly the NHS (National Health Service) has said it won't offer therapy for this annoying affliction of wanting everything just so.  :(

On another matter I decided I didn't like the studs holding the perch bracket onto the smokebox, so I made some bolts instead:



The rationale is that I have several pictures of fullsize engines and three use bolts while only one uses studs and nuts. Bolts are going to be a darn sight easier to remove. And I can see the perch bracket coming on and off a few times during the build.

Andrew

Offline Jasonb

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #162 on: September 01, 2018, 07:06:29 AM »
Looks good andrew and fixing those inverted commas will be good silver soldering practice. If you don't fancy soldering then drill and tap a hole, CSK the rear and make a GM screw that you can then CNC the bit sticking out the front to shape.

J

You now just need to get over the fact that the inner and outer rings are different colour copper alloys :LittleDevil:

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #163 on: September 01, 2018, 08:22:03 PM »
If I make the quote marks I'll make them as a pair separately and then fix the block with a countersunk screw from the back.

Andrew

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #164 on: November 27, 2018, 09:48:40 PM »
The last few months have disappeared in a Kafkaesque tale of trying to get a bathroom and kitchen refurbished; and this is still an ongoing task.  :(  However, I have made some progress on my engines. I've been working on the hinge for the smokebox door. This needed completely redesigning, as originally drawn it would have never fitted together. A member of another forum has kindly sent me lots of pictures of a full size example of the engines, so I'm trying to follow that as best I can.

Once designed the hinges are fairly straightforward machining, from lumps of hot rolled steel. The hole for the hinge pin was drilled from each end, just deep enough to clear the hinge joints. When drilling the holes I used a fixture consisting of two angle plates clamped to the mill table to give a repeatable location and to ensure the embryo hinge was precisely vertical. Just for interest I formed the curves on the hinges using a form cutter on the horizontal mill. It worked rather well:



Here are the finished hinges. They sit in a recess machined in the smokebox door. The design incorporates 5 rivets as per full size rather than the 4 shown on the drawing. Note also the small fillets at each end across the fingers where the hinge pivots will fit. I don't know what purpose they serve, but they're on the full size engine. The rivet holes in the door and hinge were drilled separately, so it's pleasing all the rivets fit with just a light tap from a tack hammer:



The hinge pivots turned out to be a right royal PITA. I made a set from hot rolled steel. No problem until I came to cut the 2BA thread on the bottom. The threads were awful with the crests torn and incomplete. I tried a number of fixes, including buying a new die. Nothing worked, darn it can't even cut a 2BA thread.  :embarassed:

After a suitable sulk time I made another set in EN1A; no problems threading this time round. Each pivot was fine tuned to its position as the orientation of the threads in the smokebox ring are random:



Finally here is the hinge assembled:



The hinge pin goes in mostly with a firm push by hand. In a couple of places I can just get a 1 thou shim between the door and ring. The shim is gripped by applying light pressure. That's much better than I was expecting, and indicates I should have no problem getting an air tight seal on the door.

Next exercise is to make the dart and locking arrangement for the door.

Andrew