Some ideas:
- Check the gantry geometry (red lines should have equal distance).
- Check that all bearing rollers on Z-axis can travel with equal pressure - if not use the excentric rollers to adjust.
- Ensure that the travel paths of bearing rollers are free of obstructions & dirt (blue areas).
- Check the geometry of the Z-axis threads (green): Ensure that the rods are not twisted by holding a ruler or any straight surface along whilst turning the Z-axis by Z-movement.
