Printer drastically changes z offset every print

General Discussion
1

Basic Information:

Printer Model: custom (vzbot’ish)
MCU / Printerboard: robin nano v3
Host / SBC btt pi v1.2
klippy.log
klippy(13).zip (640.8 KB)

Describe your issue:

around 3 weeks ago, ‘‘out of nowhere’’ i started having this issue where every single time i start a print my z offset is drastically different then the last time, i’m talk 0.5/0.7/0.9mm variations, sometimes i start a print, manually adjust the z offset while it prints via commands, let it finish, run a saveconfig and the next print i start, the nozzle is almost going through the bed, then i adjust again, save, start again and now the nozzle is floating over the bed and so on.

-i use a robin nano v3 running a custom klipper config on a vzbot330 printer with some custom mods

-my probe is a bltouch clone (worked fine before this)

-changed probe once because my older had some connector damaged, but before that also worked fine

-i haven’t changed anything on the probe part of my printer.cfg (besides checking some values, testing and then reseting to were they were)

-sometime ill start a print, the nozzle will be too close, ill stop, start the exact same file, without adjusting the z offset and it will print pefectly

-i ran that probe consistency test, it returns average numbers, all seemed fine

-bed level has been a little finicky these last 3 weeks as well, but not as bed as this offset issue

-the probe mount is fixed in place and has no play, the hotend/extruder also has no play, z movement is fine (dual motors, 4 10mm linear rods for stabilizers)

2

Likely a mechanical thing. Check:

  • Loose screws
  • Beld tension
  • Linear components running freely without binding
  • etc
3

checked everything i could think of, had a belt pop around 2 weeks ago, changed all belts on the printer, my mgn12 and mgn9 rails are both pretty new and have no issues, checked for loose stuff in general, almost took apart the entire bed assembly checking for something, frame is squared and stiff, no binding, etc.

however, yesterday, doing some more tests, i’ve began noticing a pattern, i would start a print with perfect z offset, lets say 1.8mm, the print would finish, then, the next one i started, the nozzle would be too close to the bed, around (if not exactly) 0.6mm and after that print, the next one would get back to normal, so i seems like it’s oscillating 0.6mm too close.

i ran started multiple prints yesterday, and everytime (from what i could tell) the print would do the same pattern: perfect, 0.6mm too close, perfect, 0.6mm too close, and so on (that is, if i didn’t adjust the offset, because in reality it was:
0
0.6mm too close adjusted to 0
0.6mm too far adjusted to 0
0.6mm too close, adjusted to 0
and so on

4

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