I spent a few years investigating what motor combinations could give me a wider speed range with more torque and less problems. I actually tried a 3 phase and a few DC setups. The end result is that I could not fit either the 3 phase motor and VFD controller or a DC motor and controller inside the Mark V headstock without heating problems and/or modifying the headstock. Then Shopsmith came out with the PowerPro so I quite all my testing in this area as I believe this is the most power/torque and speed range you could ever come up with for the stock Mark V headstock.joshh wrote:Answer above is correct.
For AC motors you would need a VFD (variable frequency drive) but these really only work with 3 phase motors. Any motor with a capacitor (like the shopsmith) won't work because the start circuit would turn back on as the speed slows and fubar the whole process.
I have thought about offering VFD kits for the shopsmith. That would replace the standard motor with a 3 phase reversible motor, eliminate the speed control, replace the sheave system with standard pulleys (no more oiling!), and create a custom VFD control panel that takes the place of the speed control dial on the front. Once I convince my wife to get me a good milling machine, I'll make a prototype. (Sadly years away I think)
My last attempt was an external box that I plugged the Shopsmith power cord into where I varied the frequency from 10 cps with an increasing voltage to 120 cps with a decreasing voltage. I had gotten to the test phase before my memory and reasoning ability slipped away. Everyone said it would not work but I had started to varing the speed of a small induction motor before I lost track of what I was doing. I can now remember a little about the circuits I was using but thats about it. My computer hard drive died a few years ago with all the information and pictures. I did not back up any of it.