VFD & Motor - Belt Ratio

Generally what do people run for their ratios for a vfd & motor to the spindle?

I've seen quite a bit of 1:1 & 6:1 for low torque, but finding a decent priced motor to push over 3krpm is becoming quite the issue.
I'd be looking at putting an encoder on the spindle to potentially rigid tap.


40rpm-3/4krpm is my end goal without pushing the frequency of the vfd too far (or too low). Approx 3-5hp motor, 7-10hp rated vfd.


Any one have positive results with a 'larger' setup?

One of my lathes has a 4-pole motor (1500rpm) which I push to 120Hz (for 3600rpm motor speed) and that works fairly well.

I get the extra torque of the 4-pole at 50Hz but the extra speed when needed. Final spindle speed max is 1500 rpm.

My other lathe has a mechanical gearbox with magnetic clutches to help span the range, but that goes to 3000 rpm spindle speed.