Thanks Boyan,

That was my worry. They are two separate units and don't have a common ground. Added to that one is a digital common ground for the start forward and one is an analogue ground for speed, so different I presume?

I haven't received the CNC controller yet so I can't probe any ports at the moment. I'm still trying to figure out what the lower 25 pin 0-10V port is for

Gavin