Here's some images of a 1946 Delta 17" DP I just got done restoring. It came with a 1.5 HP 3 phase motor. I couldn't decide whether to swap it with a 1 HP 1 phase motor or possibly a 3/4HP commercial servo sewing machine motor with variable speed. I ultimately decided to power the original motor with a Teco L510 VFD.
I decided to take a chance and used a 1HP 4.3 amp VFD even though the motor is 1.5HP at 5.8 amps FLA. (I could have gone with a 1.5 HP VFD but prices jump from around $150 to around $300+!!)
I also decided to overclock the motor to 1.5X max. (ie 1725 to 2587 RPM).
I'm not sure I understand all the theory, but the motor runs well under 4.3 amps from about 800 RPM up to 2587 RPM. Below about 800 RPM amps exceeds 4.3 amps by around 10%. So far the VFD has not complained.
It surprises me that amps is inversely proportional to motor speed???? I also noticed that when I apply load to the spindle at the lower speeds amps actually goes down slightly??? (power factor related???)
So far everything runs great. I've set the pulley system to give me an effective speed range at the spindle from 275 RPM up to 2175 RPM with the turn of a dial. (I programmed the VFD to indicate spindle speed vs frequency or motor RPM.)
I added remote control for start/stop and speed control at the front of the DP. I also added a main power switch since the VFD lacks an on/off switch.