Author Topic: Burrell Single Crank Compound Traction Engines - 4" Scale  (Read 35784 times)

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #15 on: June 05, 2015, 11:45:07 AM »
Ooopsie, looks like I was in the wrong place, and I've been downgraded to a supporting role.  :'(

Andrew

Online Jo

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #16 on: June 05, 2015, 11:46:38 AM »
Same as my BB1  ;)

Jo
Usus est optimum magister

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #17 on: October 09, 2015, 11:06:13 AM »
I have been struggling with the gear change mechanism over the past few months. What should have been a set of simple parts to make turned out to be anything but; let alone trying to get the mechanism to actually work.

As an antidote I've returned to gears, which I find fascinating. Almost all the gears on the engines are already made; the only ones left are on the governor. I've just spent a happy couple of evenings modelling the mitre bevel gears in 3D CAD. The LSM drawings are close on OD and face angle, but not quite right, and give no other details apart from 18 teeth and 18DP. Here is the assembly of the two gears to check meshing and spacing, as there are almost no dimensions on the drawing for the governor casting:



For scale the OD is just over 1" and the involute tooth form is for a 25 tooth equivalent spur gear, as per Tregold's approximation. It should be possible to machine these on the CNC mill, roughing with a 1.5mm ballnose cutter and a final pass with a 1/32" ballnose cutter to clean out the small end roots. Some quick CAM programming shows it should take 22 hours to machine at the maximum speed of my CNC mill, ie, 5000rpm. So I'm considering buying a high speed spindle to bolt along side. It means I lose the ability to use tool tables, but I can cope with that for a setup like this where there are only two tools.

I've also added a 3D PDF of the assembly. By clicking on the PDF you should be able to zoom, pan and rotate the gears.

Andrew
« Last Edit: August 12, 2017, 11:36:54 AM by jadge »

Offline Jasonb

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #18 on: October 09, 2015, 11:48:01 AM »
A timely post Andrew as I soon have a set to cut for my Tidman engine governor at 2:1 and about 2.5" dia for the larger wheel. I'll be following along even though I will have to opt for parallel depth method.

Nicely drawn too, did you cut-extrude one gear and then place that in a circular pattern?

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #19 on: October 10, 2015, 10:47:12 AM »
The base gear was drawn by constructing planes and axes representing the pitch cone angle and the face angle, plus lines representing the addendum and dedendum. Some while ago I found a DOS utility on the internet that generates DXF outlines of 20šPA 1DP gears from 10 to 200 teeth. An appropriate DXF is imported and all bar one tooth is deleted. That is then imported as a sketch onto the plane representing the back face. It is not exact as the back face is curved in reality, but the differences are small. In an ideal world the sketch is then lofted with a point at the origin and the resultant tooth then circularly patterned. Needless to say Geomagic is not that simple, I cannot get the loft to a point to work. So I use a 2 thou square instead. The circular pattern function seems to have a wobbly if there is overlap of the repeated shape (?), so the square at the origin is actually 7 thou above the origin. The errors caused by this are small, may be a thou or two at most, and are reduced by a factor of 18 when the model is scaled for 18DP. Here is the 1DP gear with the construction geometries:



I looked at using the parallel depth method for the design of these gears some while ago, but it all got very messy and either gave fractional DPs, or gears that weren't going to fit without a major re-design.

By playing with the CAM software I've got the machining time down a bit, but there is really no alternative to having a high speed spindle.  :) When I made my 6DP bevel gears in cast iron I was running the 4mm cutter at 4000rpm, so for the small cutters I need here running at 5000rpm is definitely pedestrian.

Andrew
« Last Edit: August 12, 2017, 11:39:09 AM by jadge »

Offline Jasonb

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #20 on: October 10, 2015, 01:16:14 PM »
Thanks Andrew, I'll have a better study of the drawing later.

I suppose you could print them out and get some lost wax brass castings done. My diff gears are cast but they do run a lot slower than a governor, suppose it depends on how much belt work you are ever liekly to do. MAybe even get them printed in metal?

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #21 on: October 10, 2015, 08:41:33 PM »
A strange thing happened today; I actually made some parts without having to scrap them and do it again properly.  :)

I tackled the worm and worm wheel adjuster for the governor. The drawings are somewhat lacking in detail, so I mostly ignored them. Rather than muck about cutting an Acme thread worm I chose to use a V-thread; in this case 7/16" UNC. For some unknown reason I already had a threading insert for 14 tpi UN series, which helps. Here are the two worms and worm wheels:



By my normal standards these are teeny weeny. The worm wheel was cut using a spiral flute tap as a hob. Last time I tried this was 40+ years ago, while I was at school. It worked then and it worked now:



Just the governor bevel gears to go now, and that will be all the gears for the engines finished.

Andrew
« Last Edit: August 12, 2017, 11:46:20 AM by jadge »

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #22 on: November 01, 2015, 08:46:37 PM »
Interspersed with weeding and digging the vegetable patches it has been a nutty time in the workshop this weekend. I've made all the 3/8" BSP nuts, and a few other parts, needed for the water pumps and boiler feed valves:



The embryo nuts were made on the Britan. First operation was to face off, chamfer, drill thru, bore out to minor diameter of the thread and part off. Second operation, using a backstop, was face to length and chamfer the second end. All pretty straightforward stuff, apart from drilling the brass; in the end I stoned the edges off the drill. Given that it's a left hand stub drill I don't suppose I'll be using it for anything else.  :) It is, however, the first time I've used a boring bar on the Britan:



I could have threaded the nuts with a BSP tap on the Britan, but wouldn't be able to thread the complete depth of the nut due to the tap lead. By screwcutting on the centre lathe I can get within one thread pitch of the bottom. It was also an excuse to buy a new toolholder for the size 11 inserts, as the size 16 inserts I normally use are too big:



After a bit of faffing about with a couple of trial nuts I got the screwcutting down to less than 3 minutes per nut at a conservative 260rpm.

Andrew
« Last Edit: August 12, 2017, 11:58:29 AM by jadge »

Offline Jasonb

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #23 on: November 01, 2015, 08:55:01 PM »
Look good Andrew, did you cut the thread in one pass or several?

I see you have an article on the Britan in the latest MEW, will have a read of that in teh week.

J

Not flying this weekend or were you fogged in? It has been very clear hear both days.

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #24 on: November 02, 2015, 11:26:48 AM »
Jason: The threads were cut in several passes. Four passes at 20 thou total cut each, plus a pass and spring pass at 15 thou total cut. That got me to the arbitrary reading of 105 on the cross slide dial. A quick check with the external 'gauge' and a final cut at a reading of 102, plus one or two spring passes at the same setting. Quicker to do than write about. That's the beauty of a high speed threading unit, no faffing about with thread dial indicators, and an automatic trip at the end so you can run the tool to within a thou or so of the shoulder. The spring passes produced rather odd swarf. For most cuts the brass comes off as a fine spray, as one would expect. However, for the spring passes it comes off as a thin crinkly ribbon. Never seen brass behave like that before. If anyone is curious I can post a picture.

No flying this weekend, but I'm tug pilot next Saturday. Both weekend days were a bit misty and Sunday went completely pear-shaped. It started a bit misty but then got a lot worse. It fooled the gliding club as on the webcam mid-morning the gliders and winch were out and ready, but you couldn't see more than a 100 yards.

I finally got around to writing the article on the Britan, sent it off, and got an email back from Neil saying it had been expedited into the forthcoming issue.  :o

Andrew

Offline Jasonb

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #25 on: November 02, 2015, 11:45:11 AM »
I think I have had similar swarf, when taking a wide cut and feeding slowly



I also find the **GT tips will produce curly brass swarf which may be due to their higher top rake than the usual shallow rake on a HSS tool

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #26 on: November 02, 2015, 08:06:34 PM »
Jason: That's the swarf type! I've only ever seen it during screwcutting with shallow depths of cut. Having just looked at some of the swarf under a magnifying glass it is of a V form. I screwcut by plunging straight in so the tool is cutting on both flanks. Thus the swarf seems to mirror the shape of the tool. It is as if each small piece of swarf cannot escape and so attaches to the next piece to produce a long curl. Certainly the crinkly swarf is not thrown off in the energetic shower that brass normally produces.

Andrew

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #27 on: December 08, 2015, 12:38:47 PM »
I am making slow, but generally positive, progress on the water pumps. The wing valves are made, as are the gunmetal valve bodies that screw into the main casting. Here are one set of wing valves, plus a set installed in the valve body:



The wing valves are made from glass filled PTFE. It's the first time I've used this material. It's waaaay nicer than virgin PTFE, which is 'orrible stuff for holding tolerances. With the glass filled PTFE it is easy to hold a few tenths.

After a false start I've also made the blanks for three rams. Material is 303 stainless steel and with a bit of fiddling on setup, and a lot of sparkout passes, I got the 10" blank parallel to within a tenth or two:



Next job is to hacksaw the ram blanks to length and finish the machining. The plan this time is to not let the hacksaw slip and damage the surface.  :facepalm:

Andrew
« Last Edit: August 12, 2017, 12:08:48 PM by jadge »

Offline scc

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #28 on: January 09, 2016, 09:09:54 PM »
Hi Andrew,   I hope the hacksaw didn't slip!     Your water pump looks different to mine.  I'm using ball valves as per Filby drgs.

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #29 on: January 10, 2016, 11:18:26 AM »
Terry: Fortunately the hacksaw didn't slip second time around!

My water pump looks different because I have completely re-designed it. There were persistent rumours on the forums that the pump as drawn was over-sized. Having run through the calculations for steam, and hence water, consumption it certainly seems to be. The ram is now 17mm (convenient as I have a 17mm reamer) rather than the original 7/8". While redesigning the ram I took the opportunity to alter the internals to use wing valves as per full size. I also changed some of the internal passages to ensure that there were no choke points in the flow. Here's a picture of the parts for one pump of the three I am making:



Three pumps? That's because I'm making one for a friend who is building the same engine. Apart from the main casting the only parts in the picture I didn't make are the M4 nuts, although I did buy a length of hex steel just in case! It will probably get used when I make the nuts/bolts for the wheel hubs. Speaking of which it's a nice day for a change so I'm now off to angle grind and weld parts for the wheels.

Andrew
« Last Edit: August 12, 2017, 12:09:56 PM by jadge »