For fractional HP I find it easier to use a PWM speed controller and a DC motor. I have a Jet Mini wood lathe that I converted to DC. The motor has an encoder so it is essentially a servo. The controller will keep the set RPM regardless of the torque requirements. The minimum speed is <> 60 RPM.
Surplus Center has several controllers for DC motors in their site at <= $50 right now, and DC motors from $10. A 2 HP - 230 VDC motor run at 90 V will still develop 3/4 HP, which should be enough for a Taig lathe.
I have no idea how to control the speed of an AC motor other than with a VFD, which is kind of expensive. |