Ian, I believe the gears inside the headstock are Mod 1.5. 
 
You can check this by measuring the outside diameter of one of them in millimetres; preferably one with an even number of teeth. If that measurement is approximately equal to (N + 2) x 1.5 where N is the number of teeth, then they are Mod 1.5. 
 
If I'm wrong and they are a different Module, use the formula Mod = OD/(N + 2). The gears are made in China, so don't expect it to work out exactly.
 
In terms of diametral pitch, Mod 1.5 is just under 17DP, so if you prefer to work in DP, 16 DP would work OK. Actually, these gears only have to mesh with each other so don't have to be to any particular standard, as long as they are about the right overall size.
 
Will it be difficult to cut the smaller gear without the cutter hitting the larger one to which it is attached? 
 
Metal headstock gears are available from LMS. They are probably noisier than the plastic ones.
 
Andy
 



To: 7x12minilathe@...
From: iannovak19@...
Date: Thu, 6 Dec 2012 06:31:07 +0000
Subject: [7x12minilathe] Re: 7x Lathe Transmission Gear Specs?

  



Thank you for your reply. I am not so worried about the specs of the gears that are right behind the cover. I am looking for specs (pressure angle, diameter, spacing between gears, pitch diameter etc.) for the Hi-Low gears inside the cast spindle head stock.

These gears are the most important for the lathe, and the most likely to break compared the the carriage travel speed adjustment gears.

If they turn out to be straightforward to make with the help of the experienced instructors, it could be a valuable learning experience and a economic decision.

Thank you,

Ian

--- In 7x12minilathe@..., SirJohnOfYork  wrote:
  

Metric. Module 1. Center hole is 12mm and on most lathes the keyway is 
3mm (there were some 7x mini-lathes with 4mm keyways, check yours if in 
doubt.) Thickness is 8mm, but I made some using 5/16" thick plate that I 
happened to have handy and they work well.

You can look at LMS to see the replacement gear sets here 
 for the plastic and here 
 for the steel sets, which list all of the 
factory gear sizes minus the two 80 tooth gears which are sold 
separately, here  (plastic) and here 
 (steel).

Useful sizes not included on the older lathes are 21 and 32 tooth 
gears, with the 21 gear being most helpful for doing closer 
approximations of metric threads with a 16tpi leadscrew (or I believe 
inch threads with a metric leadscrew, not sure where you are located or 
whether you have a U.S inch or metric leadscrew machine.).

LMS's Change Gear Page 
 is real handy 
for finding workable gear combos for threads not listed on the machine 
labels or instructions, and for seeing how the 21 tooth gear can make 
for more accurate approximations and such. To see the A, B, C & D gears 
illustrated on that page, you need to first enter in a desired thread 
and click Calculate, then scroll down to see the pictures. There is a 
spacer that is normally behind the D gear than can be swapped to in 
front of it for those gear combos where an "any" gear is specified, so D 
will mesh directly with B (instead of with C as per normal).

Cheers,
John Z.
York, Pa. USA

On 12/5/2012 10:40 PM, Ian wrote:
    

Hello. I have the resources to make my own metal gears in my machine 
shop at school. I would like to be able to make my own set of 
replacement Metal Gears for my 7x Mini lathe.

I am looking for help in finding information about the dimensions and 
specifications of the gears located in the head stock.

Thank you,

Ian