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.