I have an ex-school (UK) 'CONECT' mill. I have successfully installed MACH3 and new stepper drivers and the machine moves perfectly (with no perceptible back-lash). However when I run the spindle, using the original circuitry - modified with a speed control - the machine occasionally moves erratically. I wish to drive the motor from Mach3 but have no clue where to start. The motor is a SEM DPM30H4-33 rated at 130v 37A(?) 4000 RPM Max. I cannot contact SEM by phone and can't seem to find any simple, off the shelf, solutions being offered. Any ideas.