Trouble with homemade CNC machine glitching

[ink251]

I recently finished constructing a cnc with uses the hobby cnc 205oz motors and their pro chopper board. Using mach 3 and mastercam to program it. The machine with randomly freak out, jerking back and forth a short distance on one axs and not not moving correctly for a short time and then the program continues. It is very intermittent and this code has been verified by other machines and the mach 3 tool paths. I have a nice computer running it with a PCI parallel port card. XP Pro in Standard PC mode. Interesting to note I duabooted EMC2 and the test showed a latency value 100x more then recommended. Not really over that learning curve yet. My other concern is it might be noise. I connect the motors with cables, connect all the commons to the foil wire shield (in pictures). I did this to prevent noise but it may not be the correct way? The motors are running at 2.5a. Also the Z and Y axis wiring is ran together through a wire guide in close proximity for 4 ft+, noise an issue?

So I figure its either:
software parallel port problem
noise

Attached pictures, what do you guys think?

[metalworkz]

Hello,
Have you done any motor tuning with this machine and axis calibration?

[MrWild]

Did you connect the cable shield foil at both ends? This is BAD and will cause ground loop interference. Only one end gets grounded and the other end floats.

[MarshaJ847]

Originally Posted by MrWild Did you connect the cable shield foil at both ends? This is BAD and will cause ground loop interference. Only one end gets grounded and the other end floats.

This is true if just using it as shielding, but from the wiring diagrams for the driver board, it is being used as the return common for the four motor phase wires.

[awerby]

Foil shields are just good for case grounding; they shouldn't be used for current. How many wires are coming out of your steppers? Usually there are 4 or 6. In a 4-wire motor, each phase has a hot and a ground. 6-wire motors are pretty much the same, except you get a choice of running them unipolar or bipolar, depending on whether you hook the separate windings together. Here's a link to a simple explanation of stepper motor wiring:

http://www.ehow.com/how_4738199_wire-stepper-motor.html

Andrew Werby
www.computersculpture.com

[ink251]

Thanks for the tips guys. I wired it up where the frame and cable shielding were connected to DC - and the other end of the cable shielding is floating. Works like a charm, really was a noise issue. Thanks again for the help.