No minus Z

I have an old cnc wood router I built with ideas from this site several years ago. It worked ok till now. I run master5(from art before mach); using stepperworld's sp-3 and little japan servo steppers. Was quite cheap at the time but ok for light work. Now when I run a program Z will go positive for clearence but will not go negative into the work. The program waits for Z- and the DRO shows its moving but it doesn't. While a g-code program is running there is no holding torque on the Z motor. I swapped Z motor for Y still has no torque on Z.(I can spin the motor with my fingers). Here's the kicker, the Z axis will jog up or down with holding torque on the motor as long as a g-code isn't running or in manual! I am stumped. Any help? Thanks Paul.

I have a few thoughts. Since I haven't see the drives themselves, I don't have enough information to fully answer your question, so I'll respond with more questions.

Does the drive have an enable signal? It seem interesting that the drive produces no holding torque in one direction only. Since you swapped motors, this is not a motor problem, it's likely drive or controller related.

Have you tried to swap drives? Perhaps the controller is not providing an enable signal to the drive - this would be especially true if the enable signal was tied to the direction signal. It would display this exact symptom.

Does jogging go through a handwheel or manual pulse generator that is different than under CNC control? This would be another piece to the puzzle. Specifically, how do you jog the axes?

Please keep me up to date.

Matt

Paul,

Check your software settings. It could be a function called "Z neglect" which will ignore Z axis commands while active.

Some industrial CNC's offer this feature, too.