View Full Version : Module Gears

Shuswap Pat
12-27-2004, 03:40 PM
I am looking for some 1.75 Mod gears, to suppliment my Harrison Lathes thread cutting abilities. Any leads on an economical source?
Possibly 21, 23& 24 tooth or 42,46,48.


John Stevenson
12-27-2004, 03:48 PM
Are you sure?
Most Harrison's are 16 DP some later ones like the M300 are 1.5 mod.
Can you measure one of the ones you have and state the OD and number of teeth?

The earlier DP gears are also 14.5 degree pressure angle which are quite hard to find. The later Module gears are the more modern 20 degrees.

John S.

Spin Doctor
12-27-2004, 05:07 PM
Just like DP gears there a few oddball sizes out there. Between 1.5 and 1.57 is the 1.7 Unfortunately none of them are close to DP pitches that would allow you to cheat. But try telling my boss that. Last week he had me making helicals for a German gear reducer that would take 6 months to get parts for. But it looks like it will work.

Shuswap Pat
12-27-2004, 05:20 PM
Thanks John. The existing gears are as follows:
30 Tooth - 2.2885 OD
60 Tooth - 4.4290 OD


John Stevenson
12-27-2004, 05:37 PM
God this must be an old Harrison.
You are looking for 14 DP gears

What you do is add two teeth onto the number of teeth and divide the OD into that so 30 + 2 =32 / 2.2885 = 13.98 DP or 14.
chexk with the 60 and we get 62 / 4.429 = 13.9986 which is a gnat's cod off 14.

Bad news, as 14 DP at 14.5 Pa is like rocking horse $hit.

What are the bores on these? plain with keyway or 6 or 8 shallow splined ?

John S.

12-27-2004, 05:40 PM
The o.d. isn't going to get you an accurate measure of the p.d.

Machinery's has charts for measuring d.p. of gears using a mic across 3 gage pins, same concept as thread measuring wires - two between 3 adjacent teeth on one side, the 3rd on the opposite side. You can approximate using number drill shanks if you don't have gage pins.

You may have to guess at the pressure angle and try different tables until you get a measurement that makes sense. I'm no doubt omitting details but this ought to get you started.


John Stevenson
12-27-2004, 05:58 PM
You only use three pins on odd numbers of teeth. Pat's are even so you only use two pins.

These are cahnge wheels though and as such don't need a high degree of accuracy so this general method which is in most gear handbooks works fine.

Another thing, Machine tool builders are idle.
They tend to stick to what they had last year so parts are interchangable, that's why the majority of lathe changewheels are still 14-1/2 PA.
Myfords are still on 20 DP 14-1/2 PA same as they started out, they can't change at this point with all the lathes out there.
Stocking two types would be a nightmare.

John S.

Shuswap Pat
12-27-2004, 06:30 PM
The gears are smooth bore, single keyway. The lathe is a 13 x 40, 1970's vintage.


12-27-2004, 07:43 PM
John, thanks for your last post. I posted 3 minutes after yours and so hadn't read yours, the comment about "o.d. won't work" was directed at Pat not you, just to be clear.

I'm glad to know there is a quicker way...

John Stevenson
12-27-2004, 07:50 PM
No problem, I have often spent ages writing a post only for it to sit belows someone elses reply that says exactly what I have put.

Pat I did some gears for the Drummond group some while ago and I'm sure there was some 21's amongst then, can't remember what other sizes, 16 and 20 come to mind.
I'll check tomorrow, it's 1.00am here and absolutly pi$$ing down so I'm not going out to the shop.
What width and bore are your gears?

Shuswap Pat
12-28-2004, 11:02 AM
Greetings John. The gears are 3/4" face width, 7/8" bore c/w 1/4" kwy.


Joe H
12-28-2004, 02:31 PM

If you can't find any, MSC Industrial Supply
http://www.mscdirect.com has the cutters for 14 DP in both 14 1/2 deg and 20 deg PA to cut your own gears.

Joe H

John Stevenson
01-07-2005, 06:32 PM
Pat, Sorry for the delay, I got side tracked [ Dolly got a puncture ] http://bbs.homeshopmachinist.net//biggrin.gif

Found those gears. These are all 14DP at 14.5 PA, 5/8" wide with a 3/8" pilot bore.

I have 13T,[3 off]
16T,[3 off]
20T,[1 off]
21T,[3 off]
28T [3 off]
and a 40T with splined bore.

John S.