I’ve looked through all the issues with other types of z-probe failures (inconsistent heights, shimming corner supports, deformed corner supports with thicker modular bed, etc.). The bed is also physically level, as far as I can measure. However, I’m having yet a different issue after updating to Marlin 22.214.171.124 firmware (latest from Cura LE).
The positions where the nozzle touches down on each washer are significantly different.
- Front-Left - nozzle touches down about where it always has - halfway between the center screw and the edge of the washer
- Front-Right - position is less than 1mm from the edge of the washer
- Rear-Right - position is approximately where it was but slightly lower real y-position
- Rear-Left - position is almost on the screw in the center of the washer
The electrical contact on each corner is a little different (I assume) because of the probe positioning. Particularly, the Left-Rear contact is slightly early/high because the screw head is ~0.5mm higher than the washer.
A typical leveling output (from G29 V4) shows the corner where the nozzle touches close to the screw head (Left-Rear) as 0.5mm higher, which makes it impossible to get the z-offset set correctly, print a consistent first layer, etc.
Send: G29 V4 Recv: G29 Auto Bed Leveling Recv: Bed X: -9.000 Y: -9.000 Z: 2.811 Recv: Bed X: 288.000 Y: -9.000 Z: 2.801 Recv: Bed X: 288.000 Y: 289.000 Z: 2.731 Recv: Bed X: -9.000 Y: 289.000 Z: 3.349
What could be causing the leveling routine (baked into the firmware) to be so far off of the physical bed corners? Is there something besides the extruder steps/mm and the z-offset that needed to be restored after upgrading?
REF: Marlin/Conditionals_LulzBot.h · v126.96.36.199 · LulzBot 3D / Marlin · GitLab
Things I have already checked…
- Both x and y steps per unit (mm) were 100.50 before and after updating firmware, and nothing mechanical has changed there (same belts, same tension, same stepper motors, same controller board, same wires and connectors… so unlikely the steps per “real” mm would need to be adjusted).
- Print bed carriage is not mounted askew (at least no more than a fraction of a mm) - checked with a straight edge against the front and back plates / feet of the frame, and with a square against the extrusion rails of the main X/Z part of the printer frame.
Have not tried to downgrade to the previous firmware version but it’s on my list if I run out of more plausible things to check.