Warco WM16 Mill - Conversion to AC motor with VFD

[birchy]

Ideally do both - keep the gears (or much better replace them with timing belts) and then add the induction motor. The power output from an induction motor will reduce with speed, when driven from a VFD, so it's best to keep some form of gearing so that you can still have a useful amount of power at low speeds. The other option is just use a huge motor, but that's often not practical/sensible/economical.

If I go to an induction motor, I'll most likely get rid of the main input gears between the motor and gearbox and replace them with a belt drive. Vee belts are not out of the equation as they WILL slip in the event of an accident. But then again, do we need to minimise slip and use timing belts?

The existing 600W DC motor is a gutless thing at low speeds, so I'd be looking at maxing out the VFD with a 1.5kW motor. IIRC, the Altivar drives have a few functions for "torque boost" and "constant torque" which may help.