Hi, Tom
One way is to use a DPDT ON ON switch, Run your rot. table step & die wires to the center terminals, Mach3 A axis S/D to one side of the switch and a LM555 oscillator to the other side.
This would allow you to set a cont. speed for your spindle/rot. use and switch back to A axis use.
PM your phone # if in USA / CA, I'll give you a call after 9:00 Eastern tonight.
Thanks, Chip