Geeetech Thunder: Z homing makes X gantry tilt — right side “binds/knarls” at the bottom, first layer impossible (back-right too close)

3D Printing
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Hello everyone and happy easter,

I’m Felix from Germany, and I’m looking for help troubleshooting a Geeetech Thunder. Here’s a video: https://youtu.be/4KKS4yWMjlg

My X gantry (the horizontal beam the toolhead rides on) does not stay level after homing, and it causes immediate first-layer failures. Copilot helped me summarize and translate this. That’s why the following looks like an AI text.

What’s happening (symptoms)

  • When I press Home XYZ (or when a print starts and does its homing), the Z axis moves down.

  • Only at the very bottom of Z travel, right around the moment both Z sensors should “trigger” (flag/plate goes into the sensor), I hear a grinding/creaking/knarling sound, I think mostly from the right side. See the video above.

  • After that, the printer does the typical small move up a few mm and down again (homing “bump” / re-home step).

  • During that small up/down movement, the gantry becomes visibly tilted: it looks like the right side sticks / hangs, while the left side continues moving, so the beam ends up not horizontal (right side slightly higher).

  • After homing, the gantry is still slightly tilted. I can see it with a spirit level, although I’m not 100% sure the gantry is ever perfectly level relative to the bed.

Important:

  • This issue happens only at the bottom during homing / print start.

  • If I move Z higher up (several cm), I get no strange noises, and the gantry seems to stay aligned during normal Z moves.

How it affects prints

  • First layer is inconsistent across the bed:

    • Front-left: good nozzle gap, extrusion/adhesion looks OK. PLA with suggested temperature (i believe 210°C), bed at 60°C. speed 100mm/s. slicer: cura ultramaker

    • Center and especially back-right: nozzle is too close → scraping / barely extruding / no adhesion → print becomes impossible very quickly.

  • It feels like either leveling compensation can’t fix it, or the gantry is already tilted right from homing. when I use babysteps, i can’t get it right on the whole bed. only for some parts of x/y axis (like when i print really small things)

What I’ve already tried

  • :white_check_mark: Reflashed printer firmware (mainboard firmware).

  • :white_check_mark: Reflashed the display/UI firmware (Geeetech calls this “UI upgrade”, using a System folder on SD/USB).

  • :white_check_mark: Adjusted eccentric nuts / V-wheels so there’s no play (toolhead + axes).

  • :white_check_mark: Checked for coupler / leadscrew slip:

    • Drew alignment marks across leadscrew + coupler metal piece → no movement/offset. Marks stay perfectly aligned whether I move Z by centimeters or press Home and watch it go crooked.

  • :white_check_mark: Turned the leadscrews by hand (printer off): both turn easily, no hard spots. red side turns a bit harder.

  • :white_check_mark: Adjusted the flag/plate height that enters the sensor:

    • Originally the flag/plate heights were different (right was higher than left).

    • I was able to adjust the left flag/plate upward, so now both flags/plates are at the same height.

    • Problem still remains.

Extra observations

  • The noise is only when homing at the bottom.

  • At the sensor board I can see two adjustment points labeled something like “D+” and “E+” (looks like tiny adjustment screws / trimmers). I haven’t messed with them yet.

  • I’m new to 3D printing and the printer did print well earlier on. I tried stuff that Copilot suggested but hours went by and no steps forward.

Thanks for your ideas!

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That’s definitely mechanical, I believe. The noise sounds to me like a stepper motor skipping steps. So one side is binding and the other side isn’t.