A customer has a gear program that didn’t do internal sun gears. It wasn’t friendly.
The law curve capability in NX12 is excellent. You are able to quickly input four equations; t=1, xt=f(t) yt=f(t) and zt = f(t), then access the law curves ability on the curve tab. It will make the appropriate curve. In this case the equations perform the involute gear tooth profile.
Find out exactly how you can do this too and see samples. Gears in motion
Also download the .prt file .PRT Download