Prusa Mini Z-Axis Fail Self Test Solution (length of Z axis rod)

Does your Prusa Mini fail its self test wizzard on the Z-axis?

This can be due to several issues. The item printed here relates to failure due to the length of the Z rod. A simple fix and one i didnt initially believe would work.

Process: You need firmware verion 4.3.2 or above. Insert a usb stick, run the self test wizzard. It fails on the z axis, let it complete and say the test failed overall. Remove usb and place in a PC/Mac. There are 3 txt files generated with test results. One file is for Axis. Open that file, scroll all the way down until you get to the end of the Z axis result.

It should be around 185mm i believe, mine said this:

length = 191.069992 mm
Z-Axis Failed
SELFTEST END

I made a clip-on spacer 6mm high for one of the vertical bearing rods, to effectively reduce the open rod length to 185mm. It clips on nice and tight, but not too tight. Its wide enough so its just wider than the linear bearing (to avoid the bearing being pushed out when the bearing hits the spacer) and actually the spacer will touch the plastic surround of the bearing.

Once the spacer is clipped to the outer vertical rod, push it to the top of the Z axis. It must of course be above the extruder/z-motor :) The spacer will grip firmly and remain at the top of the rod.

Re-run the self test wizzard. Hopefully it will pass the test. (if it fails again make sure to use the usb to obtail the latest results). If there is still no luck there may be another reason.

If your ‘length’ is different in the report, you may need to reduce or extend the spacer thickness. The STEP file is included, making it easy to amend thickness.

I'm not sure if the fact i have a Bondtech extruder had any affect to cause this failure, as the original extruder seemed to have a similar profile.

Printed in Petg @ 20% infill at 0.3mm

I hope this troubleshooting option is helpful.