"Was that too complicated to understand? Try this: If you can figure out how to put a VFD between the switching relays/drum switches and the spindle motor and still be able to run the feed motor, speed changing motor and electric brake (maybe a coolant pump, too) while maintaining the original operating control functions without wrecking the VFD, go for it."
I don't understand what's that complicated.
1) put the varispeed sheaves mid-range.
2) hardwire the spindle motor for high range.
3) the feed motor is a *dc* motor. It's run off single phase. No need to feed it via the VFD.
4) coolant pump? Few HLVH owners use that, but a static converter would would be fine for that if one insisted.
Yes. The owner needs to understand how to wire up a VFD direct to the spindle motor, and remove all the
items inside the box on the left side of the machine. Yes, the owner will have to be minimally conversant with
electricity.
Pro electrician? Maybe. Most lathe owners would do this on their own, at least the ones who cross over between
the 'lectrics and VFDs sub-board, and the hardinge sub-board.