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

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