I’m running into issues with z-axis sync issues with my Prusa i3 MK3/S. I’d like to force both z-axis steppers to the top, ensuring that the x-axis is level, before each print. Specifically, I’m looking for the proper gcode to force the z-axis past the boundary that works with Prusia’s firmware.
I remember hearing Tom mention in one of his videos that he uses some gcode to force the Z-axis all the way to the physical top of the frame to force both z-axis steppers back into sync. That sounds like exactly what I want. Unfortunately, I can’t remember which video this was in, since I’ve binge-watched dozens of them in the last month. I think it may have been a live stream; during one of those impromptu discussions triggered by chat. (Next to impossible to search for.)
I’ve been periodically noticing that the z-axis stepper motors are getting out of sync just a little. Typically it’s not bad enough to trigger a z-axis alignment warning during the 3x3 bed leveling, but enough that it’s causing prints to fail from time to time. I don’t know if there’s multiple cause for this, but I know for sure that I’ve caught my kids walking by the printer and manually turning the z-axis threaded rods. I’ve been burnt by this a few times now, trying all kinds of things before realizing the real source of the issue. Fixing this by hand requires (1) remembering, and (2) manually running the Z-axis half-way up, resetting (to clear the z-axis location info), and then finally running it all the way to the top, but not too quickly so that it doesn’t grind against the for any longer than necessary. (And, if I get too aggressive, holding down the turn knob too soon during the restart, then the printer wants to factory reset, instead of move the z-axis, which is NOT what I want!)
It seems like if I knew the right gcode, I could just drop it in the “Start G-code” section in Prusa Slicer (right before the G28/G80 home/mesh-level sequence) and then never worry about this again.
Does anyone know the proper gcode to tell the printer to run the Z-axis all the way to the top to hit the physical limits?
What I’ve tried so far
G1 Z210; Stops short of hitting the physical top G1 S1; Disables boundy checking? Nope, does not work M45 Z; This "works" but runs the full calibration \w user prompt G34 - Z Steppers Auto-Alignment; Sounds promising. Response: Unknown G code M120 - Disable Endstops - Listed on Prusa Wiki page of gcodes. No luck.