Hi, I’m Jadon and I’m running Mach4 on a CNC router with an external motion controller, and I’m seeing a strange issue that I haven’t been able to track down. If Mach4 is left idle for more than a few minutes with the machine enabled, the Z axis still jogs and homes normally, but the moment I start a G-code job, Mach4 suddenly reports a motion fault and ignores all Z moves in the program while X and Y continue running. There’s no E-stop triggered and no following error shown, but the DRO for Z freezes at the last jog position and the tool just air-cuts. Restarting Mach4 temporarily fixes it, which makes me suspect some kind of state or buffer problem rather than wiring. I’ve checked soft limits, probe settings, and motor tuning, and nothing stands out. Has anyone run into Mach4 losing axis motion control only after sitting idle, and where should I be looking to diagnose this properly?

the forum probably needs to know your motion controller.

motion controller would help. Also if your using external drives, make sure and turn off the driver sleep function. DM542's have a switch for half-current

Does changing the 'Idle Timeout' setting in Mach4 affect this error?

Hi, I’m Jadon and I’m running Mach4 on a CNC router with an external motion controller, and I’m seeing a strange issue that I haven’t been able to track down. If Mach4 is left idle for more than a few minutes with the machine enabled, the Z axis still jogs and homes normally, but the moment I start a G-code job, Mach4 suddenly reports a motion fault and ignores all Z moves in the program while X and Y continue running. There’s no E-stop triggered and no following error shown, but the DRO for Z freezes at the last jog position and the tool just air-cuts. Restarting Mach4 temporarily fixes it, which makes me suspect some kind of state or buffer problem rather than wiring. I’ve checked soft limits, probe settings, and motor tuning, and nothing stands out. Has anyone run into Mach4 losing axis motion control only after sitting idle, and where should I be looking to diagnose this properly?

It does sound more like a motion controller or plugin state issue than a wiring or motor tuning problem, especially since the Z axis can still jog and home correctly after sitting idle. The fact that the DRO freezes when the G-code starts suggests Mach4 may not be receiving proper position feedback or motion confirmation from the controller for that axis. I would check the Mach4 diagnostic and plugin logs immediately after the fault occurs and see if there are any communication or buffer-related messages. It's also worth looking at whether the Z drive or controller has any idle timeout, sleep, or watchdog settings that could affect programmed motion but not manual jogging. Another useful test would be to let the machine sit idle until the issue appears, then run a very simple G-code file containing only Z moves. Also, which external motion controller and plugin version are you using? That information could help identify whether this is a known controller-specific issue.

Hi,
I've been using Mach4 for ten years and have never had the problem you describe.

I seldom de-power my machine, and Mach4 can stay on for many weeks, and even on occasion months at a time. I rock up to the machine and start work, I usually do not
even re-home, as the machine has not lost reference from its last use, and I can go for weeks like that.

As williamcorlin has posted I think that suggests a problem with the motion controller or its plugin rather than Mach4. After all if it were a Mach4 problem would not all user be subject
to the same bug?

Craig