Strange behaviour: Oscillating print bed

[HansMeiser 0]

Greetings, my fellow printers! :)

 

Since about a month I am a happy owner of an Anycubic Mega Pro and so far everything works very well. At least as far as I can tell as a beginner. My already many prints have turned out well so far, there have been no serious problems.
Also, I have already read in depth into the matter, especially for the settings of a 3D printer. Because the bed leveling was somewhat unclear to me at the beginning, but is now clear. After I have printed already some, I wanted to re-level the print bed. In the process, I noticed (and thus remembered) something that I had already noticed the first time.

The print bed oscillates in height. What do I mean by this?
When I level the print bed, I use the Anycubic menu to do it. That is, I let the print head move to the respective corner points and use a sheet of paper for the spacing.
Now the effect:
I adjust the print head so that the paper can be pulled with slight resistance. A few seconds later, however, the sheet moves (almost) without contact. Again a few seconds later the slight resistance is felt.
And this is repeated again and again. Hence "oscillating."And this is the case on every corner of the print bed.

This oscillating is also noticeable in a 5-square print test with 1 layer. The area of the squares are thicker and sometimes thinner. Depending on where on the surface this oscillation is happening.

Now I would like to know if a) someone knows this phenomenon and b) how it can be fixed.

The prints themselves look like this doesn't create a serious problem, but of course I'd prefer it if this "up and down" didn't happen during printing.

Any suggestions?

[GregValiant 1,251]

Put a finger on the Z coupler of the lead screw and see if you can feel it "oscillating" back and forth.  I don't know enough about stepper motors to advise but it would seem that either the mainboard isn't settling down, or the stepper can't decide where it should be.  Swapping wires with a different axis motor would be a good test.  If the problem moves to the 2nd motor, its the mainboard.  If the Z stepper still oscillates then it's the motor.

[HansMeiser 0]

Thanks for the reply!

Too much tech for a newbie like me. 🙂 Maybe because I hoped for a "simpler" solution.

I have to find the parts you mentioned and look into it.

 

In the meantime, if anyone has another suggestion, please let me know. I need to learn more.