While printing large flat surfaces, I just noticed that the right front Z lead screw turns visibly, and I can even see the bed move up and down a little. Just to be clear, this is not Z hop, which is a sudden jump. This is a gradual turn as the print head moves.
I recently manually trammed the print bed. First I followed Bambu’s instructions. Then I reran the tramming gcode, which sets the print bed at a 0.4mm offset below the print head, and used a feeler gauge of 0.4mm thickness to ensure that the distance is the same for all three positions and is snug.
I would therefore not expect to see much movement on the Z axis during XY motions.
I also recently put a support ticket in with Bambu, where I provided the printer logs. They said, “the bed mesh data appears to be in good condition.” What “good condition” means is probably a bit subjective. Should I be questioning that claim?
Yes. As I mentioned, not only did I follow the instructions, I used a 0.4mm feeler gauge to double-check that the tramming had in fact achieved the same distance between the print head and the bed in all three test locations.
The three jackscrews that raise and lower the bed are all synced with the toothed belt. I can’t say for sure but what I think you are seeing are the jackscrews compensating for any height errors the system found. You’d need to gauge the whole bed at each point where it made measurements to know you were getting a good read with the feeler gauge. It’s probably fairly possible the points you tested with the feeler gauge were indeed 0.4mm spaced but do other positions and maybe not?
I can see mine moving the bed up and down slightly to put the area being printed at print height. I mean that literally - mine does the same thing. The jackscrews are turning a few degrees back and forth as it prints top layers on a piece and the head is moving back and forth across the print.
I think it’s normal but maybe there is some other issue if yours are turning a lot.