Thanks for the update Bob.

That is what I am trying to figure out. The revs can be quite slow and I am wondering how to drive such slow revs. You indicate about 7.5"/min is good for TIG. So welding a 2.375" dia. tube would be about 1 rpm but if you were welding a 14" dia. car rim then the rpm is slowed down to about 1/5 RPM. That is a 5:1 ratio and I was wondering how to get that kind of range in a power supply and still have torque at such a low voltage.