As I thought, there are so many pulley combinations with the countershaft that I decided to put them in a spreadsheet – just to make it easier to organize. I know that I’ll probably settle in to using two or three combinations most of the time anyway, but I’ll always have these handy should I need them. It looks like the highest RPM is going to be 1733, so if I need more than that, I’ll just have to hook the motor up directly to the lathe. Assuming I have the formula correct, here are the screen shots:
I hope someone finds this useful. Thanks to David and Bob for their help with the calculations.