and welcome to the forum.
There are two possible reasons for that behaviour I can think of.
- dirt or grease between the motor and the drive wheel (under the leather wheel). Clean it and try to use some sandpaper on the surface of the drive wheel. A rougher surface with some "new" rubber exposed will give new grip.
- if that's not the reason, it might be a faulty capacitor.
Is your Tormek machine older or brand new? In any case I'd contact Tormek support, they'll help you find what causes the problem ...and how to solve it, too.