Learning curve!

[IanH]

Help!

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.

[CNCRouterMan]

There seems to be a ground problem. Noise is causing the problem. Check to make sure you have good grounds and the wires that are running your spindle is insulated away from stepper motor wires in the e-chain .