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Mystery Gears

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Keith Long26/01/2011 16:03:08
883 forum posts
11 photos


Hi Everyone

I've just up loaded a picture of a set of small gears that I've acquired via E-Bay. The seller didn't have any idea of their origin, and I'm hoping that for interests sake someone here might be able to shed a bit of light.

The details of the gears are:-

28dp, pressure angle unknown. The gear wheels have a 7/16 inch bore with a 1/8 wide keyway. The 3 pinions are all 20 teeth, and have a plain bore of 3/8 inch. The gears are 0.400 inch thick, but you will see in the photo that the pinions are of different lengths (thicknesses), the shorter being the same as the gear thickness, the middle very nearly twice the gear thickness (but with a very slanted end and the third being 2 and a half times the thickness of the gear wheels. The only mark I've found on the wheels apart from tooth count is the following stamped onto the end of one of the pinions "SM 40/3".

The numbers of teeth look a bit of an odd progression being, 3 x 20 (the pinions), 30, 40 ,48, 70, 80, 88, 106, 116, 117, 119 and 120. Putting those numbers into the "nthreadp" program and guessing a use with either an 8 or 10 tpi lead screw shows that it would be possible to cut most imperial threads up to about 70tpi and most metric threads with an acceptable accuracy to about 2mm pitch, the 10 tpi lead screw being better for the metrics.

At 28dp they seem a bit small for a set of lathe change wheels, although I believe the mini lathes use 1 mod gears which are very similar, and the of the set of gears I have, the spoked are made from cast iron, as I suspect are the 30, 40 and 48 wheels. The pinions I don't know about, they would be just as easily made from round bar stock.

I intend to use them for index purposes as they have some useful numbers of teeth that include most of the primes to 20 and being 28dp are half the size of my lathe change wheels so should leave more room, when used on the cross or vertical slides, to see what I'm doing.

If anyone has any ideas where these may have originated from, or what machine they've come from I'd be very interested to know.

Many thanks

Keith

I've popped this in the General Questions topic area as I'm not even sure they come from a mahcine tool - could they be for a model of some sort?

Edited By Keith Long on 26/01/2011 16:07:55

ady27/01/2011 00:19:04
612 forum posts
50 photos
Looks like a bit of a heinz57 varieties of wheels to me, the bore being the main reason they were purchased.
 
If it's any help it may be Britannia lathe stuff, they did various spoked wheels for some lathes, old smart and browns also had spoked wheels.

Edited By ady on 27/01/2011 00:31:25

John Olsen27/01/2011 07:27:09
1294 forum posts
108 photos
1 articles
If they were lathe change wheels I would have expected to see steps of either 4 or 5 teeth. Myford uses 5, some of the Drummonds used 4.
 
(eg 20, 25, 30, 35, 40, 45.... or 20, 24, 28, 32, 36 und so weiter.)
 
Of course over the years one or two might easily get lost. YOu might not see a nice progression the same with wheels for a metric leadscrew, since the metric series is not designed to make change wheels or gearboxes cheap and easy to make.
 
regards
John
Keith Long27/01/2011 21:22:17
883 forum posts
11 photos

Hi

Thanks for the suggestions.

Ady I see what you mean about the Smart & Brown gears although the spokes look to be a different pattern. A very early issue of MEW had a design for a quick change gearbox to fit a Myford and that used 28dp gears, but very different tooth numbers, but it has got me thinking that if the 3 pieces of the pinion had originally been one long gear then there would be about 2/3rds of the bits needed for a quick change box, but again with those tooth numbers it would be anyones guess as to what machine it was. Could even be from a special purpose machine.

Keith

ady28/01/2011 10:24:16
612 forum posts
50 photos
With the spoked gears being cast gears there's also the possibility that company A had them made by company B.
 
Britannia made a ton of different designs so if you're a wee firm or you don't want to set up a foundry just for making gears then you would subcontract it out, especially if it was a cheaper route.
 
Some firms did this with leadscrews, since it made sense to have a critical part made at a different firm who had a high quality leadscrew making machine which could bang out exactly what you needed in the quantities you wanted.

Edited By ady on 28/01/2011 10:24:40

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