Yeah, the start capacitor and its centrifugal cutoff seem to be the fly in the ointment. I did a little reading on VFD's in wikipedia (which makes me a leading expert ). They can be used with universal or induction motors, 3 phase or 1 phase.
They also say that the VFD delivers more torque per amp at startup. They use the soft start principle seen in var speed routers to slowly ramp up the juice. This creates the same torque with half the current at startup.
I'm wondering if an induction motor with the capacitor and centrifugal switch removed would start under those conditions. If nothing else, in a belt drive system (not much help for the bench grinder) using an idler to remove the load at startup, it would likely work.
I have an arbor and pulleys that I used to spin my 8" stone and buffer on, but I don't have a spare motor to play with. And I don't have a VFD. Before anyone says the obvious - yes, I know it's easier to reduce the rpm's here using pulleys
Now, if anyone wants to send me a free Baldor grinder (postage paid, of course) and a suitable VFD - I'd be happy to perform the necessary experiments. Don't thank me, guys - my offer is made in the name of science !!
All the best,
**Now holding auditions for a catchy new signature**