I've never thought about using a treadmill motor for a lathe application, and it sounds interesting. From a load/electrical standpoint, it would seem to be a good choice as it is subjected to periodic loading as when a runner is running. A person that weighs say 200 lbs. can exert the equivalent of 800 or more lbs. of force when jumping so the motor has to be subjected to similar loading as when cutting with a gouge, for example. Good idea.