Quote Originally Posted by JohnT View Post
Thanks Doody. Yes I checked with a multimeter and the Bob shares it's grounds. I was looking at those isolation boards. I checked the motor controller and measured the 0-10v terminals against each other and to machine ground. I'm getting 270v DC and 9v AC with the multimeter. I don't have an oscilloscope. I'm leaning towards ordering one of those isolation boards. But if it doesn't work I could blow the motor controller etc. I'm thinking feeding one end of the isolation board to the 0-10v terminals on the motor controller and the other end to the 0-10v output on the Bob. Use a transformer power supply to feed the vcc and ground. Or else not risk it and let linuxcnc control the SGR relay and use a potentiometer to control the speed.
From what I squinted at with that particular board the circuitry was visible separate from the LV and HV sides. You’d supply the LV from the general machine supplies and the HV from the reference voltage provided by (most) spindle controllers (is these that you’d otherwise write a speed control pot to). It’s low risk and you can test with a meter easily. I wouldn’t have much fear of going this route.