Re: Adequate torque from VFD driven motors?

Thanks to those who replied. The theory is now clearer, but the
practice still poses questions.

The lathe I am working on is a 50's vintage Rockwell 11" with what they
call a "perfected" VS 1 1/2 hp drive. (Yes, it has functioning back
gears.) The amalgam of sliding sheaves, bearings, shafts, cams, gears,
etc seems awfully complex to restore and maintain compared to an
electronic VS drive, provided that performance would be equivalent or
better.

A VFD controlling a 3 ph motor came first to mind, since I have on hand
many 3 ph motors to choose from and the VFD could be run from a 1 ph
supply with suitable derating. The suggestion that a larger than
original motor may be required gives me some concern - doesn't that
create a possibility of greater-than-design torque at higher speeds
that could cause harm to the machine, or even operator if a
catastrophic failure occured?

Perhaps a dc motor and controller would be also worth considering,
especially if that would address my concerns about low-end torque while
keeping the 1 1/2 hp factory spec.

So, how do ac & dc spindle drives compare in terms of cost,
performance, availability, and ease of CSS implementation. And how do
the several dc control approaches compare?

TIA

Steve Clay-Young