Author Topic: Burrell Single Crank Compound Traction Engines - 4" Scale  (Read 41418 times)

Online Kim

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #45 on: April 22, 2016, 06:04:49 AM »
Hi Andrew,
I'm following along and enjoying watching your build, and learning!  Not a lot of comments from me, cause I don't have much to add.  But you're work looks beautiful to me!
Thanks for sharing!
Kim

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #46 on: April 22, 2016, 10:37:39 AM »
Thanks for the comments; I'm not planning to stop posting, just curious as to why no comments.

Jason: Not so much the flying getting in the way at the moment as airworthiness reviews (sort of like an MOT). I've done 9 so far this year and at least two more to go, excluding getting some-one else to sign the ARC for my aircraft.

If I recall correctly the slotting head was happy with about 4 thou per stroke for a 5/16" slot. With narrower keyways it's happy with higher feeds.

As I understand it gear verniers measure the chordal thickness at the chordal addendum. The addendum and the tooth thickness across an arc of the PCD depend only on the diametric pitch. But the gear verniers can only measure linear dimensions, so both the chordal addendum and chordal thickness change slightly according to the number of teeth. For the 20 tooth 5DP pinion the difference between addendum and chordal addendum is about 6 thou, and between tooth thickness and chordal thickness less than a thou. Even allowing for the corrections the parameters we are interested in measuring do not depend on the shape of the involute away from the pitch circle. And therefore should not be affected by the fact that the form of an involute gear cutter is theoretically correct only for the lowest tooth count of the range of a given cutter.

The difficulties I had were mainly practical. If the gear vernier isn't exactly vertical over the tooth, and isn't exactly perpendicular to the gear axis you get false (over) readings. It became apparent that I was chasing my tail with the measurements and wasting time doing further cuts for no benefit. The price of a new 456A Starrett gear vernier is $1473. I'm glad I only paid around 20 for mine on Ebay!

Andrew

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #47 on: May 07, 2016, 11:59:58 PM »
Having recently described the gears, including the crankshaft pinions, it seems logical to have a look at the machining of the crankshaft. The cast crankshaft comes with two integral lugs to allow turning of the crankpin. The first operation was to drill two centres at each end at the correct spacing for the throw. I used the vertical mill and DRO to ensure accuracy, and used the mill right-angle attachment for the first time:



With the crankshaft mounted between centres on the lathe the crankpin was machined using a insert parting tool sticking a long way out of the holder. A series of plunge cuts were made and once the rough cast surface had been removed the parting tool was used to take shallow cuts sideways to reach the correct diameter:



Once the crankpin was machined the crankshaft is located between centres on the second set of centres and the main shaft rough machined. Then a fixed steady is used to machine the shaft to length and a new centre drilled. Finally the shaft is machined to size:



For the second half of the shaft the previously machined feature can be held in the collet chuck. I had a lot of chatter problems when machining the main crankshaft. The only solution seemed be fairly aggressive feedrates. The chatter was probably partly due to the fact that I chose not to use jacks to increase the stiffness of the crankshaft. I've only had severe chatter problems once before, when machining the front axle. That was SG iron too, so I wonder if it a characteristic of the material? Poor damping possibly? I am sorry to say that one of the crankshaft journals for the eccentrics has ended up undersize.  :embarassed:

The final part of machining the crankshaft is the splines for the drive pinions. The standard way of machining these is to use a dividing head on the vertical mill and an offset cutter to produce the sides of each spline. The waste material between the splines is then removed by a series of cuts, rotating the crankshaft a small amount each time. Alternatively the splines can be created by milling slots and then fitting keys to mimic the splines. I didn't feel that either of these methods was ideal. It is possible to buy commercial spline cutters that create the gap between the splines, in a similar fashion to involute gear cutters. However, no commercial cutter was available for the size of spline I needed. So I decided to make my own cutter.  :ThumbsUp:  The cutter was modelled in 3D CAD, with relief, and machined on my 4 axis CNC mill from gauge plate. The roughing cuts were parallel to the axis of rotation of the cutter, and the finishing cuts were perpendicular to the rotation axis. Here the roughing cuts have been finished and the final cut is in progress:



There is a compromise between the stepover distance for the finishing cut and machining time. In this picture of the finished cutter (before the drive key slot was machined and before hardening) the finish cut stepover can be clearly seen. However, some gentle draw filing with a needle file removed the high spots:



After hardening and tempering the cutter was used to cut the splines on the horizontal mill:



I am embarrassed to say that the width of the splines varies by a couple of thou over their length, probably because I didn't take care to ensure that the tailstock was exactly on centre height. Fortunately the mating pinion gears only travel a short distance on the splines. So the final filing to ensure a snug fit of the pinion gears can be tailored for the postion of the gears on the splines. And you'd never know looking at it.  ;)

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

Online yogi

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #48 on: May 08, 2016, 02:04:08 AM »
Fantastic work Andrew!  :ThumbsUp:
That spline cutter turned out beautiful.
Thank you for sharing your techniques.  :cheers:

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #49 on: May 10, 2016, 06:48:37 PM »
Hi Yogi,

Thanks for the compliment. As well as the spline cutter I've had a go at making some square thread taps and a hob for free hobbing a worm wheel. Generally I've been pretty pleased with the way all the cutters have turned out, and the job they've done.

Andrew

Offline Mcgyver

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #50 on: May 10, 2016, 07:04:34 PM »
very nice work on challenging parts, thanks for posting it

Offline zeeprogrammer

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #51 on: May 11, 2016, 01:11:48 AM »
I hadn't seen a right-angle attachment before. Not that I remember anyway. That's cool.

But the cutter is awesome. Just as awesome as making a part, no?
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
"To work. To work."
Zee-Another Thread Trasher.

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #52 on: May 11, 2016, 11:27:49 AM »
Zeeprogrammer: Agreed; if anything making the cutter was more interesting than cutting the splines, especially as I hadn't made this sort of cutter before.

The right-angle attachment (Bridgeport No. 3 I think) also comes with a arbor and a support bracket that fits on the Bridgeport ram, so it can be used for horizontal milling. I have used it in this mode, but a caveat is that it is only suitable for light milling. For heavy milling I use my horizontal mill, which makes the Bridgeport look lightweight.

Somewhere I've also got a Quillmaster for the Bridgeport which comes with it's own dinky right-angle attachment, but as yet I haven't used it.

Andrew

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #53 on: May 14, 2016, 10:53:14 AM »
FOr the idly curious this is the Quillmaster and dinky right-angle accessory that fits on it:



I call it chicken and egg tooling. If you haven't got one you never consider designing a part that may need it. On t'other hand if you do have one you never seem to have a need for it.

Speaking of Bridgeports mine clunked more than usual yesterday afternoon and then the spindle coasted to a stop. It happened just after I'd countersunk the wrong hole. Turns out it was the varispeed drive belt that had broken. I've changed this before so it only took me an hour or so to change this time. The manual isn't a whole load of help. When removing the motor it talks about using some screws from a cover plate to hold the drive cones apart before removing the motor and belt. Of course this don't work if the belt is broken.  :'(  Once I wrestled the motor out and got in on the mill table, without dropping it or falling off the ladder, I used the trick I eventually worked out last time. You hammer the old drive belt into the cones and this prises them apart enough to get the screws in place. The belt doesn't damage the cones, and the cone angle, and friction, is such that it doesn't ping out. The new drive belt seems quieter than the old one, so I hope it will last a bit longer.

Andrew
« Last Edit: August 17, 2017, 10:23:12 PM by jadge »

Offline scc

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #54 on: May 29, 2016, 11:38:28 AM »
You have certainly got some nice equipment there Andrew,  I'd love to do my own gearcutting.       Nice gliding weather this weekend?
Best Wishes,          Terry

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #55 on: May 29, 2016, 08:48:19 PM »
You have certainly got some nice equipment there Andrew.............

That's because I suffer from OIS - old iron syndrome. I just can't stop buying it.  :embarassed:

Not great gliding this weekend. I was tug pilot yesterday afternoon. After a lot of low cloud in the morning I eventually did a couple of tows late afternoon. They were both passenger flights and wanted to get to 3000ft. I declined to climb above cloud, as the blue gaps were too small, the visibility was very poor, and there is a large American Airshow at Duxford this weekend. The exclusion zone is only a few miles from us; I'd look a right wally if I got lost above cloud and infringed the zone. I got to 2700 feet on the first tow before deciding it was time for the glider to go, as I couldn't tell what was cloud and what was just haze. On the second, later, tow we got to 3000 feet in the murk, but below cloud.

Today was similar, low cloud all morning, breaking up mid-afternoon. I'll probably work tomorrow, despite it being a public holiday. I really want to do more grinding and welding of the T-rings on my rear wheels, but I don't suppose the neighbours will appreciate some idiot spending hours angle grinding on a Bank holiday.  :ThumbsDown:  So I'll work tomorrow and take a day off later in the week to do the wheels while everyone else is out at work.

Andrew


Offline scc

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #56 on: May 30, 2016, 10:32:08 AM »
You are right Andrew, neighbours and angle grinders do not mix.               Terry

Offline scc

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #57 on: May 30, 2016, 05:06:11 PM »
Tug pilot, glider "MOT" person,    do you ever get the chance to fly your own?

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #58 on: June 01, 2016, 11:00:38 AM »
Tug pilot, glider "MOT" person,    do you ever get the chance to fly your own?

Not as often as I'd like. I haven't flown my small glider at the local club this year, although I have done a few flights in the big glider. So far this year the weather has been poor too. It seems to be mostly low cloud and murk. I am trying to take one day off each week to either fly a glider or work on the traction engines.  :ThumbsUp:

Andrew

Offline jadge

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Re: Burrell Single Crank Compound Traction Engines - 4" Scale
« Reply #59 on: July 13, 2016, 08:53:44 PM »
As an antidote to gears I've finished the water pumps, and delivered the third one to my mate in return for folding drinking vouchers. Here is one pump assembled and all the parts for the second:



All the parts for the pumps, including nuts, bolts, studs and washers, apart from the 4BA nut (upper centre) are home made. The two wing valves (centre) were machined from glass filled PTFE, which machined beautifully, unlike pure PTFE which is 'orrid stuff to machine and hold tolerances on. The spacer (bottom right) is a fancy shape just for the hell of it, and because it's easy on a CNC mill.

The key to machining the main casting was an 'angle plate' drilled and tapped for the casting and made from aluminium extrusion, plus a steel spacer block which eventually became the fancy shaped spacer. Here are some examples of the angle plate and block in use. The first operation is to drill, ream and bore the ram bore and gland recess:



In a different orientation to drill, ream and screwcut the overflow valve spigot:



And the last operation machining and threading the outlet spigot. This was the only thread on the casting cut with a die. The 3/8" BSP die was held in the tailstock with special home made die holder that was thin enough to pass between the outlet spigot and the bolt down spigots:



Not only was the aluminium angle plate multi-purpose for the water pump casting it was original made and drilled for holding the main gear change casting. Pretty good for an offcut acquired from the scrap bin of my commercial aluminium supplier.  :ThumbsUp:

Finally here is the water pump in place on the hornplates:



I have also been busy making the eccentric straps and sheaves. So once I've made the water pump eccentric rod I can connect everything up and see if it goes round. And, more to the point, see if my 3D CAD model is correct and that the few thou of clearance between the eccentric rod and ram is positive.

Andrew
« Last Edit: August 17, 2017, 10:28:23 PM by jadge »