i have a breakout board that has PWM capability , from what i can gather. i haven't got around to the spindle side of the build yet! i'm trying to get my head around getting these motors to turn and getting the inputs to signal. i was hoping to get the M/C up and running with the basic controls and safety functioning and when i become comfortable with the operation going back at the spindle control. for the time being i would use the VFD . if the PWM doesn't work out , then i would definitely go the route of the link you posted, in fact it would be quicker to adjust a pot and have an instant response i would think, especially if the pot was mounted in a home made pendant that could be brought to the front of the M/C? i have my machine e/stop on a lead that i can mount either side of the machine on a hanging bracket and i could incorporate the pot and some other controls as i become more familiar with the process. by the way , is my understanding of how i should incorporate the e / stop to the BOB correct? i'm reallly not too sure if i'm right.