Z Axis sag ruins levelling

I left a print going overnight and took off the result in the morning. Left the printer on. Then tried to do another print and the nozzle gouged the bed on the left side.

Turn the printer off, lift both z towers as high as they’ll go, print again and it’s fine, don’t even need to re-level.

I guess at some point overnight after it had finished the steppers were disengaged, and the toolhead caused the left z tower to drop.

So I guess this is an advice post - turn machine off and reposition both z towers after it has been idle for a while, otherwise your levelling is ruined cause the controller doesn’t know the left axis has moved.

This makes me quite sad. I hope SM have considered new splitter modules which can drive each axis individually, then the controller can at least attempt to do something about this.

Do you have an M18 or M84 with delay in your gcode?

I am not aware of the machine ever turning off stepper on its own, although perhaps that’s a change in the most recent firmware.

D’oh! I have an M84 in my ending sequence. User error!

Thanks Brent


Although… if sag happens when I disable steppers, it will also happen when the machine is switched off between prints.

Does your start gcode not do a home? The snapmaker calculates it’s axis positions by bumping the end stops when it does a home, you should be doing that before every print.

I am, but the machine stops when either of the endstops are hit, not when both are hit. Thus, if the machine is skew on powering the steppers, it is always skew, as it lacks the ability to control each tower independently