I have a vfd on my BP but since fitting it's been left set at 50Hz so just a phase converter really.

I am now converting the old girl to CNC and trying to figure out what to do with the speed control.

Is it workable to set the vari-speed knob in the middle at say 1500rpm, mark the position, and then calibrate the VFD to control from say 500 to 3000rpm?

I know back-gear will still be needed for torque/low speed but that could be treated the same maybe?

What's a good way of treating this system?

Fitting a plain pulley head is not really an option as it means buying another machine and butchering it.