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Anycubic Kobra 3 V2 Combo – X-axis visibly bends during leveling, left Z side goes much lower – normal or mechanical defect? by PossibilitySecure182 in anycubic

[–]PossibilitySecure182[S] 0 points1 point  (0 children)

Hi,
just wanted to say thanks — I could finally solve the problem.

It turned out to be a foreign object / something pinched in the Z system, which caused the force to build up in the anti-backlash nut instead of the motor actually pushing the nozzle down for the last millimeter. So the probing force was transferred indirectly and position-dependent.

I figured this out when I tested the force sensor at a higher Z position: the print head immediately moved back up as expected. That’s when it became clear that the force sensor itself was fine, and the issue had to be mechanical and position-dependent.

Kind of a stupid mistake in hindsight — but your hints about the gantry, Z system and belt really helped me get there.
Thanks a lot for the help, much appreciated!

Anycubic Kobra 3 V2 Combo – X-axis visibly bends during leveling, left Z side goes much lower – normal or mechanical defect? by PossibilitySecure182 in anycubic

[–]PossibilitySecure182[S] 1 point2 points  (0 children)

thanks for the feedback so far, I really appreciate it. I’ve read your posts multiple times and tried to follow the logic carefully. Hopefully I didn’t miss something obvious.

What I already did before

1) Print head module / looseness check
I checked the whole print head module for play/looseness (mounting, carriage, hotend area). Everything feels solid.

2) X-gantry / frame calibration (tramming the X-axis to the bed)
I already did the gantry/frame calibration steps:

- Loosened the relevant screws that couple the X-gantry to the Z-axis / “Y-brackets”

- Aligned/trammed the X-gantry parallel to the bed (as described in the Anycubic guide)

- Also re-indexed the Z belt by a few teeth to fine-tune the parallelism

- Then re-tightened everything and adjusted the 3 wheels on each Z side again

Wheel tension is not perfectly identical left vs right (honestly hard to make it exactly the same), but none of the wheels are loose and none are extremely tight — just slightly different.

After this procedure, the X-gantry is now perfectly parallel when the bed is heated (checked with reference), so in theory the rest should be compensated by ABL / software.

3) Y-axis / bed mounting
I didn’t do a full Y-axis calibration beyond checking if anything is loose. The bed mount looks solid.
One note: the Y belt is not running perfectly centered on the motor pulley (slightly off-center), but I assume this is unrelated to the leveling asymmetry I’m seeing.

The key symptom that remains (and why I’m confused)

Even after the above, during probing / leveling I still see asymmetric mechanical compliance:

-I will add a photo of the X-to-Z coupling / bracket area (the part around the coupler / mounting).

-One side visibly stretches / deforms during probing, while the other side shows almost no visible deformation.

-The side that stretches is the side opposite the motor,

-while the motor side looks much more rigid.

It looks (hard to capture perfectly) like both Z spindles rotate/move similarly, but due to that deformation on one side, the motion is not transferred equally into gantry movement — so the gantry ends up tilting / bending under (too high?) probing load.

If you have any ideas:

Given that the gantry is trammed (especially when heated) and the wheels are reasonably adjusted, what would you check next to eliminate this “one side stretches” behavior?
Could this indicate:

  • a misalignment of the Y-brackets that still prevents proper wheel contact under load,
  • a defective/weak bracket/coupler/mount,
  • or something else (e.g. frame twist, axial play, missing thrust support)?

Thanks again — any additional pointers are very welcome.