Z axis drift when motors off

I just finished with my MPCNC assembly. I have mounted a Makita spindle. One potential issue is that the Z axis now has enough weight that with any slight bump it can over power the friction on the Z axis ball screw and drift down into the machine bed. This does not happen when the motors are powered on. The Z axis rail bearings don’t feel loose and I can still turn each bearing with my fingers. Should I tighten up the bearings more or just leave it until the ball screw accumulates dust from use?

The bearings won’t keep the router from dropping. The bearings should be touching the tubing, but not tighter than that.

The dropping can be fixed with procedures. You just need to park the router before disabling the motors.

You can also change the leadscrew with a 1 start. The downside is that you will lose top speed on the Z axis, because the motor has to turn 4x as fast (and steppers lose torque at higher speeds).

When you say “1 start” are you describing the lead screw thread pitch?

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Yes. Exactly.

The Z axis dropping is a common problem on the Lowrider, but I don’t remember ever hearing about the issue for an MPCNC. Maybe you have such a precise build there is little friction on the Z axis. If it were me, I’d 3D print a clip to be attached to the closer Z axis tube before disabling the motors. I doubt you need much to prevent the Z axis from descending. Note that all the bearings should touch the Z axis tubes.

It has been an issue a couple of times. Usually the router is running, which causes vibration enough to get it started.

See, this is all you need. If the motors are off, they will go down, even faster when the router is still on. There is a command in the G-Code that does not power off the motors. There is also a setting in Estlcam I think. Mine are not powering down, so Z does not go down either. :slight_smile: