[QueueJr]

Hey all,

I've got a NM-145 that's having some strange problems with the z-axis. It seems to be losing it's position. Sometimes when I jog up, the position counter increases on the controller, but the machine does not move. If I home it, the counter will continually increase well beyond the limits of the machine (70+ inches? I don't think so). Eventually, the z-axis will start to move and when it hits the home position, the counter will reset to the appropriate number. This problem only happens with the z-axis. To make matters worse, sometimes it seems to work just fine and I haven't found any reliable explanation for what causes it to work certain times and not others.

I've taken apart the machine, cleaned and lubricated where necessary, and made sure the home switch inside was free of any debris that might be interfering. I would guess the problem is either the motor or an incorrect signal from the controller software (Mach 3 v R3.043.022).

Does anyone have any insight or suggestions? Thanks.

[rpovey]

Sounds like your missing steps.
Could be mechanical, or noise,but I'd start by turning down the ZAxis speed and acceleration in Mach, see if that fixes it.
Turn the down dramatically if that fixes it, it's just a question of tuning them back up.

[QueueJr]

I'm pretty sure the step is not the problem. I've tried moving the Z-axis with speeds as low as 0.5% jog and it doesn't move at all. I've also ruled out the motor by swapping the motors on the X and Z-axes. The problem persists, so it's definitely a control or home switch issue and not a motor problem.

[rpovey]

If it's the homeswitch, the axis would move up until it hit the mechanical stop and mach would continue to count Z, unless you have set your home switches as stops, that's the only effect it should have.

Just to eliminate it try turning the acceleration on the axis way down.
If it's too high the axis will stall intermittently when it tries to start moving.

Turn off any backlash compensation in Mach when testing, if it's configured badly it can do the same thing.

You should also try enabling Sherline mode in Mach, just to see if it has an effect, if it does, it's not the right fix, but it's a data point.

Unfortunately the other potential issues are harder to track.
Rule out the driver by swapping a working axis with Z.
Try and rule out mechanical issues, the coupler, gibs too tight etc.
After that you're down to noise issues, and they are no fun to track down.

[QueueJr]

Thanks, all good suggestions. I've ruled out backlash compensation, and axis acceleration. The Sherline mode setting didn't seem to do anything. The most likely issue now is the stepper driver. Either a bad connection, or the driver itself. As soon as I can, I plan to swap the stepper drivers on the Z and X and see if the problem persists. Unfortunately, I'm in the middle of a production run and I can't afford the downtime to troubleshoot.

In the meantime, it's developed a new problem. Occasionally the Z-axis motor will forget how to reverse. Jogging down moves down. Jogging up moves down. Dangerous if the bit is close to the vise or part. I've given up running anything CNC while it's losing it's Z-coordinates, but I've been able to proceed running manually so I can move slow and check the position. When it freezes I can simply re-zero and continue, but as long as the up-is-down problem persists, I can't make any progress.

[rpovey]

Up is down can only really be a couple of things.
Bad wiring, a loose wire is enough to do this, there is a single pin on the driver if that pin has voltage it goes one way, if it doesn't it goes the other.
Bad driver (same logic).
Mach, I've heard of this problem with pirated copies (not suggesting your using one).

Just as a point of reference I'd take 10 minutes to go through the electrical cabinet and make sure all the screw terminals are tight.
I just replaced the PSU board on mine (shipping damage) and in doing so found a couple of loose wires.

If yours has the same drivers mine does, swapping the drivers over is a 10 minute job, everything is on removable terminal blocks, it's just unplug plug.

[QueueJr]

Problem solved! As I suspected, the Gecko motor driver was to blame. A simple tightening of the wires seemed to fix the problem, but I'm ordering a replacement driver just to be sure.