Creating a set of changewheels

Happy New Year all!

I have an Adept ordinary lathe that I am upgrading as near to watchmaking quality as possible.

I have read the article from 1947 by L.V.P.Clarke, who did much the same, and used 50DP gears. I’m going to do things in metric, as I am a railway Modeller, so intend to use 0.5 module.

The problem is, I can’t work out what size the set of gear blanks has to be. I have Ivan Law’s Workshop practice book, but try as I might, I can’t find out what size to make each gear blank. I must be missing something important!!

Can anyone point me in the right direction, please?

I want to make a standard set:

20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 90 and 120 Teeth.

Mike

Edited By Mike Waldron on 01/01/2023 10:23:16

Edited By Mike Waldron on 01/01/2023 11:20:01

Mike,

HPC Gears tables give the overall dimension for various counts….should help as a starter…

https://www.hpcgears.com/pdf_c33/23.10-23.13.pdf

I’m away so can’t look it up, but I’m pretty sure the calls are in Ivan’s book.

The diameters relate to the number of teeth and the module size.
I seem to remember it’s something like number of teeth + 1 divided by the module, but that might be pitch centre or totally wrong…

Dave

I think it is (N+2)*module. Page 57 of Law's book, LH column.

When this question comes upon the forum, I always recommend Geardxf download, a freeware program from forestmoon.com. It not only gives all the gear dimensions you will ever need, but covers DP and MOD gears too and you can export the results to dxf file, as the name implies.

John

edit: corrected hyperlink

Edited By John Hinkley on 01/01/2023 10:55:52

+1 for John Haine. The result is the O/D of each blank, in mm. N is the tooth count

Brian

Mike,

As above, for 0.5mod all you do is take your tooth count, add 2 then divide the result by 2. So your 120 tooth gear would be 61mm diameter.

Very many thanks all for your help!

A first time for everything!

Now I can get going!

Mike

While what you say is true in this particular case, it is a bit of a poor way to express the maths. The division by two is actually multiplication by the module, which in this case just happens to be 0.5.