Author Topic: Burrell Single Crank Compound Traction Engines - 4" Scale  (Read 35785 times)

Offline scc

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #30 on: January 10, 2016, 01:45:16 PM »
beautiful work

Offline zeeprogrammer

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #31 on: January 10, 2016, 01:56:34 PM »
Nice family shot and excellent work.

Just caught up on this thread. Wish I'd been more active earlier.
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
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Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #32 on: January 10, 2016, 05:41:56 PM »
It might be best if those of a sensitive disposition look away now! The wheel welding isn't pretty, although in my defence it's the first time I've done any serious arc welding. However, I don't think it's going to fall apart, and I hope that once I've used the angle grinder to remove the spatter, and odd lump, plus a good dollop of U-Pol it'll look alright:



The wheel jig seemed to work fine and kept everything more or less in line. Not perfect by any means, but probably better than the originals!

Andrew
« Last Edit: August 17, 2017, 09:51:21 PM by jadge »

Offline scc

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #33 on: January 18, 2016, 10:42:44 AM »
Hi Andrew,   I wonder if you have made the expansion link yet, and if so is the lsm drawing ok?  I know that the conrod drawing is a joke  and wanted assurance from a tech expert before I cut metal.               Cheers              Terry

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #34 on: January 31, 2016, 08:02:27 PM »
Terry: I'm embarrassed to say that I've only just seen your post regarding the expansion link. :embarassed:  I made an expansion link and die block in gauge plate to the LSM drawings, but that was for somebody on the TT forum. He had a professionally built engine, but it was rather worn and he was replacing parts as required. Once I get on to the motion work I plan to re-design the valve gear, but that is quite a way in the future. Some people say that the LSM valve gear design leaves something to be desired, but others who have engines built to the drawings say they run fine. Take your pick!

This afternoon after wielding a hot arc welder I have finished welding all four front wheel rims and T-rings:



I'm getting better at arc welding. Once I've finished all the wheels I'll be good enough to start again and make the wheels to a proper standard. The next welding job is to turn 32 quadrants into the T-rings for the rear wheels.

Andrew
« Last Edit: August 17, 2017, 09:52:38 PM by jadge »

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #35 on: February 26, 2016, 08:57:38 PM »
Elsewhere on this forum I mentioned that I'll try and post about a few more parts already made for my traction engines. For those that want more detail I run a build diary on TractionTalk under sobriquet 'oly2brf5'. On the same forum I am running a theory thread, although it has been in obeyance for a while due to work pressures. On the Model Engineer forum I am also involved in a thread on the theory and design calculations for steam injectors, although again it is temporary obeyance.

Now on to parts - in this post bevel gears, because I like gears. My traction engines have a differential based on two bevel gears and three bevel pinions. Traditionally there are two ways to cut approximations to bevel gears using standard equipment.

The first method uses an involute gear cutter, takes three passes and results in a tapered tooth form. The first pass is on the axis, followed by two offset passes that widen the space between teeth at the outer edge of the gear. I have made bevel gears using this method in the long distance past. However, there are two problems, the first concerning the involute cutter. It has the correct curvature for the involute form at the outer edge of the teeth, but since it has to pass through the narrower gap at the inner end it is narrower than a standard cutter of the same DP. These cutters are normally stamped 'BEVEL'. However, they do not seem to be available now - when I made the bevel gears all those years ago I had the facilities of the Royal Aircraft Establishment main workshop at Farnborough behind me.  :ThumbsUp: The second issue is the curvature of the teeth at the inner edge is not correct, and needs adjusting with a file or similar.

The second method treats the teeth as being constant depth, and can be cut in three passes with a standard involute cutter. However, in this method the gears are designed using the DP at the inner edge, not the outer edge as is standard. This means that it is very difficult to design gears to fit into an existing design while retaining an integer value for the DP.

Now, if I could design the bevel gears in 3D CAD I wondered if it would be possible to make proper straight tooth bevel gears using a 4-axis CNC mill? The answer was yes! The design process was quite long winded. It's one thing to pontificate about gear design but quite another to put numbers on things. For instance everyone knows that the tooth form is based on the involute of a circle, but which part of the involute and which circle? It turns out that it is the involute of the base circle, the diameter of which is the diameter of the pitch circle times the cosine of the pressure angle. Having drawn the gears in 1DP I created an assembly in CAD to check the meshing and face to face distance (note the undercutting of the pinion teeth):



The observant might note that the teeth on the bevel gears look rather rack like for a 36 tooth gear. This is because the shape of the tooth is determined not by the number of teeth on the bevel gear, but on the 'equivalent' spur gear. The number is given by the number of teeth on the bevel gear divided by the cosine of the face angle. For my pinion this gives a value of 10.3 instead of 10, so use 10 teeth, ie, no change. However for the gear we get a value of 134.5 instead of 36, so use 135 teeth. The method is known as Tregold's approximation. To get the CAD models for the 6DP gears I need just use the CAD to scale the gears by one sixth.

That's enough flavour of the theory, onto the practical. Here are all the gear blanks and one of the pinion blanks ready on the 4th axis of the mill:



Note that the pinion blanks are simply cylinders. The bevel gear blanks were originally castings, but I fouled up on some dimensions and had to ditch the castings. The blanks shown were machined from continuously cast iron bar - lovely stuff to machine apart from the dust. The bevel pinions were machined with one cutter, a 4mm diameter ballnose. First a series of cylindrical roughing passes were done followed by a profiling pass with a fine stepover. The profiling pass is being machined in this picture, although the roughing passes can be seen:



The bevel gears do not need the 4th axis for machining as they are relatively flat:



The bevel gears needed several passes with different cutters. First roughing passes with a 4mm ballnose cutter, followed by a profiling pass with a 3mm ballnose cutter. Finally there was another profiling pass with a 2mm ballnose cutter to clear out the roots of each tooth. After several broken 2mm cutters I twigged that I needed to chamfer the inner edge of the bevel gear first, unlike the bevel pinions where it was done after machining the teeth. Here are two sets of finished bevel gears complete with bronze bearings where called for:



And finally all the parts for a complete differential:



For scale the ring spur gears are 10.833" and 11.833" OD. Note that the three pivots for the pinions (centre of picture) have a threaded hole in the end. That's so one can get the darn things out if disassembly is needed without having to resort to naughty words. In due course I'll write a few words on the differential centre and ring gears.

Andrew
« Last Edit: August 17, 2017, 09:57:24 PM by jadge »

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #36 on: March 07, 2016, 10:55:08 PM »
Following on from my previous post here are a few notes on the differential centre and ring gears. The observant will note that the differential centre is painted red, or not, in some pictures. I forgot to take any pictures of the machining of the differential centres when I did mine. A while later I cut the pinion slots and cut the ring gears for a friend who is building the same engine. He had already protected his differential centre with red paint.

The turning of the differential centre and ring gears is straightforward faceplate work. I used the diddy 12" faceplate as this saves mucking about removing the gap piece and then replacing it correctly. Once machined the slots and holes that take the pins for the bevel pinions can be milled, drilled and reamed in the vertical mill using the dividing head. The paper towel stops the worst of the cast iron swarf getting into the 3-jaw chuck. Hidden behind the towel my dividing head has a handy reversible plate on the spindle with 56 and 60 slots. So this simple divide by 3 stuff can be done without faffing around with dividing plates:



The slots into which the bevel pinions fit were cut using the rotary table. The rotary table is set up so that the T-slots are aligned with X and Y axes on the mill when the table reads zero. The DRO is set to zero at the centre of the rotary table. The differential centre is mounted central and such that one of the slots aligns with a T-slot on the rotary table. The four corners of each slot can then be co-ordinate 'drilled' using the milling cutter. The top and bottom of each slot can then be cleaned using the X axis on the mill table. The position and width of the slots are important as they control the engagement of the bevel pinions and gears. The sloped sides of the slots are machined by turning the rotary table ±22° around each slot and then using the Y axis of the mill to join the holes in the corners, by eye. The sloping sides are for clearance only.



In theory cutting the two ring gears is simple - they're just spur gears. However, two practical problems arose. First, my dividing head has a 5" centre height and I needed 5.9". So I had to make some riser blocks from a lump of hot rolled steel. The blocks for the dividing head and tailstock were made as one and separated at the end to ensure that they aligned. Here is the slot for the dividing head being checked against a length of 5/8" gauge plate. The slot that holds keys for the table has already been machined and is being used to align the block during the machining of the second slot:



When the blocks were split and machined to width two horizontal 'V's were stamped on the edge, so all I need to do is have the 'V's pointing at each other to ensure proper alignment. The second problem is more interesting. The ring gears have 63 and 69 teeth, neither of which is prime, but they cannot be cut using simple indexing with the standard division plates. Rather than mess about with gears for differential indexing I decided it was easier to make a special dividing plate with 63 and 69 holes. Very simple using the bolt circle function on the vertical mill DRO, if a little tedious. Just to be different the manufacturer of the dividing head chose to make the three countersinks in the centre of the plate 60° rather than 90°. I used a large centre drill to create the countersinks:



Finally the gear cutting:



Note the special green clamp! In an ideal world the cutting forces from the involute cutter should create no torque on the gear. I cut all the small spur gears for the engine with no problems. However, on the first 69 tooth gear the cutter didn't cleanly enter the first tooth once I'd been round once - it was about 15 thou out. I spent ages checking and re-checking the maths and the indexing. This showed that only the last few teeth were out, so near the end the darn gear must have slipped slightly. Although it couldn't be seen it annoyed me, so I scrapped the gear, bought another casting and did it all again. This time the green clamp holds the blank against a small angle plate bolted to the mill table for each cut. You live and learn, and the wallet suffers in silence.

Andrew
« Last Edit: August 17, 2017, 10:04:28 PM by jadge »

Offline Kim

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #37 on: March 08, 2016, 03:13:18 AM »
Nice gear cutting Andrew!  And I love the special green clamp :)
Kim

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #38 on: March 08, 2016, 01:28:09 PM »
Kim: The green clamps, called crab clamps I think, are really great. Here they are in use this weekend assisting in the welding of laser cut quadrants to make the T-rings for the traction engine rear wheels:



I bought them through 'Model Engineer' some time in the late 1980s. I recall there being some problem with delivery. Being a fully paid up member of the awkward squad I regularly rang the advertising manager at the publishers for about a year, until she decided it was easier to get the problem sorted, as I wasn't going to go away otherwise.

The 6DP involute cutter for the ring gears was the only one I bought new. I ended up buying from Victornet (?) in New York. Of course it's an 'import' but at least it is 20°PA. Although such cutters are available in the UK they all seem to be 14½°PA, but I'd already decided to use the more modern 20°PA. All the other 6DP, and 5DP, cutters I needed, plus a few I didn't, were bought secondhand from the US via Ebay - bargain.  :ThumbsUp:

Andrew
« Last Edit: August 17, 2017, 10:07:37 PM by jadge »

Offline scc

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #39 on: March 08, 2016, 08:12:03 PM »
Looking good Andrew...............Terry

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #40 on: March 10, 2016, 10:29:09 AM »
Looking good Andrew...............Terry

Thanks Terry.  :ThumbsUp:  Progress on the wheels is frustratingly slow. One problem being that it's not worth getting the welder out and everything set up for an hour or so, but finding several consecutive hours is an issue. If nothing else the gliding club membership is finally coming out of hibernation and I'm getting lots of requests to review and sign off the ARC (Airworthiness Review Certificate) for assorted gliders. It takes quite a few hours for each review. The ARC is a legal document certifying that the glider is airworthy and hence fit to fly. So one doesn't want to make a boo-boo!

In the meantime here's a completely OTT use of the green clamps to hold the connecting rod tapered lock to CNC machine the round/tapered section at the top:



Andrew
« Last Edit: August 17, 2017, 10:09:23 PM by jadge »

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #41 on: April 21, 2016, 01:24:00 PM »
This thread seems to be attracting a steadily increasing number of views, but no comments. I'm not sure if that's good or bad?

Anyway, here are a few more gears, specifically the crankshaft pinions and final drive pinions. Here is one set of pinions, along with the arbors for holding them during gear cutting. On the right are a couple of ground arbors to check the bore size.



On the left is a gear vernier. When I first started cutting gears I did a roughing and finish pass with the cutter and checked the tooth width with the verniers. It turns out I was wasting my time. I now cut gears in one pass; all that two passes does is wear out the cutter. Likewise the gear verniers weren't much use. For non-precision gears like these it is fine to touch off the cutter on the OD and then move the mill by the theoretical depth of the tooth and commence cutting. You live and learn. Unless of course you do something really daft and get a Darwin award.  :facepalm:

The final drive pinions are 5DP in cast iron and are straightforward machining. The crankshaft pinions are 6DP in EN8. The horizontal mill cut the EN8 like it wasn't there:



The crankshaft pinions as shown thus far have been scrapped. When I made the first set I was ignorant about machining EN8 and didn't get a good finish, as can be seen. I was also concerned about the fit of the splines and made the bore 10 thou bigger than specified for clearance. Sometime later, with more experience, I machined another set of EN8 gears for a mate, and got a much better finish. So I remade mine, and also reduced the bore to the proper size. I found that the key to a good finish on EN8 is surface speed. The new sets of pinions were machined at 800-1200rpm, using insert tooling.

Once I'd made the crankshaft thoughts turned to cutting the internal splines in the pinions. I wanted them to look neat, so I puzzled about how to get the correct radius on the end of the tool to be used in the slotting head. Eventually I twigged that I could use the cylindrical grinder to grind a diameter that I could measure, and then cut the toolbit in half and grind the reliefs by hand:



Here is a rather poor picture of the slotting in progress on a scrap blank (I cut the gear selector slot in the wrong place) as a trial. The pinion is mounted centrally on a rotary table. Relatively fine cuts were needed or the Bridgeport slotting head jammed:



The pinions required some work with needle files to achieve a good fit on the crankshaft splines. Not least because the width of the crankshaft splines vary by a thou or two over their length, but that's another story.  :'( Finally here are the proper set of crankshaft pinions in place and one of the final drive pinions just visible at the bottom of the picture:



Andrew
« Last Edit: August 17, 2017, 10:16:08 PM by jadge »

Offline Steamer5

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #42 on: April 21, 2016, 02:03:57 PM »
Andrew,
 Don't worry about the lack of comments, just keep the updates coming ...PLEASE !! It's just gob smacking work, would be nice to sit & watch the work on the cutting of the gears.

Cheers Kerrin
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Offline steamer

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #43 on: April 21, 2016, 02:36:39 PM »
This thread seems to be attracting a steadily increasing number of views, but no comments. I'm not sure if that's good or bad?

Anyway, here are a few more gears, specifically the crankshaft pinions and final drive pinions. Here is one set of pinions, along with the arbors for holding them during gear cutting. On the right are a couple of ground arbors to check the bore size.



On the left is a gear vernier. When I first started cutting gears I did a roughing and finish pass with the cutter and checked the tooth width with the verniers. It turns out I was wasting my time. I now cut gears in one pass; all that two passes does is wear out the cutter. Likewise the gear verniers weren't much use. For non-precision gears like these it is fine to touch off the cutter on the OD and then move the mill by the theoretical depth of the tooth and commence cutting. You live and learn. Unless of course you do something really daft and get a Darwin award.  :facepalm:

The final drive pinions are 5DP in cast iron and are straightforward mchining. The crankshaft pinions are 6DP in EN8. The horizontal mill cut the EN8 like it wasn't there:



The crankshaft pinions as shown thus far have been scrapped. When I made the first set I was ignorant about machining EN8 and didn't get a good finish, as can be seen. I was also concerned about the fit of the splines and made the bore 10 thou bigger than specified for clearance. Sometime later, with more experience, I machined another set of EN8 gears for a mate, and got a much better finish. So I remade mine, and also reduced the bore to the proper size. I found that the key to a good finish on EN8 is surface speed. The new sets of pinions were machined at 800-1200rpm, using insert tooling.

Once I'd made the crankshaft thoughts turned to cutting the internal splines in the pinions. I wanted them to look neat, so I puzzled about how to get the correct radius on the end of the tool to be used in the slotting head. Eventually I twigged that I could use the cylindrical grinder to grind a diameter that I could measure, and then cut the toolbit in half and grind the reliefs by hand:



Here is a rather poor picture of the slotting in progress on a scrap blank (I cut the gear selector slot in the wrong place) as a trial. The pinion is mounted centrally on a rotary table. Relatively fine cuts were needed or the Bridgeport slotting head jammed:



The pinions required some work with needle files to achieve a good fit on the crankshaft splines. Not least because the width of the crankshaft splines vary by a thou or two over their length, but that's another story.  :'( Finally here are the proper set of crankshaft pinions in place and one of the final drive pinions just visible at the bottom of the picture:



Andrew

Jadge.....just too much going on, on my end.....please proceed!   I'm watchin...

Dave
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Offline Jasonb

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #44 on: April 21, 2016, 04:04:53 PM »
Quote
Likewise the gear verniers weren't much use. For non-precision gears like these

Andrew is that because we use involute cutters that will cover a range of tooth numbers, do the verniers only work with gears cut on a proper machine with a true form?

What sort of feed does the slotting head need, I did mine the hard way planing in on the lathe and 0.001" per pass was all I wanted to lhe the lathe cope with, at least the Fowlers are flat topped.

Looking good, I hope the start of the flying season won't slow progress too much.

J