# Thread: Need help on measuring spur gear

1. Senior Member
Join Date
Jan 2006
Location
Indianapolis
Posts
194

## Need help on measuring spur gear

I am attempting to measure a change gear from a Grizzly G9972Z 11 x 26 lathe in order to make two mating gears. These gears will be part of a reverse tumbler. What I believe I have determined from an existing spur gear is; 35 tooth, root diameter is 1.281” (32.54mm), outside diameter is 1.452” (36.88mm). Using my 10x magnifier lenses, the pressure angle looks very similar to the chart in machinery’s handbook showing 20 degrees.

Is this enough information to calculate the dimensions for a 36 tooth mating gear? How do I go about these calculations? I have studied the machinery’s handbook but still do not understand. I would like to make a single point tool for a fly cutter and use a spindexer in the mill to make these gears.
Thanks

2. Senior Member
Join Date
Mar 2001
Location
Nottingham, England
Posts
16,177
Gary,

From your figures and knowing that the Grizzly is an import take the OD, add 2 to the number of teeth making 37 and divide this into the OD.

To all intents and purposes it comes to 1 which is 1 MOD the metric equivalent of spur gears.
1 Mod is equal to 25.4 DP in imperial terms.

3. Senior Member
Join Date
Jan 2006
Location
Indianapolis
Posts
194
Thanks John. If I understand correctly, the diametrical pitch then is 25.4. Using this link www.doov.com/cgi-bin/tgc_spurgear.cgi, I input the diametrical pitch as 25.4, number of teeth as 36 and the pressure angle as 20. The program return the other values needed to make the gear.

4. Senior Member
Join Date
Mar 2001
Location
Nottingham, England
Posts
16,177
Yes, had a look at the output and that's all you need.

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