Quote Originally Posted by EddyCurrent View Post
At the end of the day I would be looking to convert an S value in gcode to a combination of inverter speed and contactor selection, does that sound correct ?

So what is the relationship regarding gcode S value, inverter frequency, contactor selection, spindle output speed equal to gcode S value ?

If that can be determined then it looks like a Mach3 Brain can be used. If you watch the video linked to above you will see that their example has similarities to your own requirement
You've lost me a bit there, but I'll take a look at the video.