Help with gear calculation

Hi all,

I'm trying to calculate the dimensions of an internal gear ring. It is 72 tooth 1.25 mod 20 deg PA.

Can I use the same calcs as for an external gear or are there additional compensations to take into account on an internal gear,

It will be meshing with a 36T pinion.

thanks in advance

Graeme

ok, I've done a bit of digging around and I;ve come up with an internal dia of 3.34" or 84.93 mm. Can anyone confirm if I am even close?

ta

Graeme

Clearer picture here **LINK**

Hi Graeme

I thought you were asking how to generate the tooth profile so I kept schtum.

If it's just the basic dimensions, then the same as the external gear, except the dedendum is subtracted from the inside diameter and addendum added to the outside diameter - in effect the tips of the teeth and bottoms of teh gaps have exchanged places.

Neil

JS, thanks, thats exactly what I needed, what software are you using there?

Neil, thanks, thats what I thought, from what JS provided I can see I was almost in the right ballpark.

Graeme,

It's a program called Gearotic motion written by Art Fenarty, the original writer of Mach3.

GM is actually defunct and has been superseded by a program called Gearotic Thought which has more features but I like the simpler earlier version better.

Link here. **LINK**

Art has done his customary licensing for life deal and once you sign up, all updates and new versions are for free.

Can't say enough about it, so far it's earn't me some serious coin.