Auto-level bug

I encountered a problem with several prints (at least 3). On longer ones there's a drift on Z that occurs randomly. All is good during some time then the layer thickness becomes greater and filament no more stuck to model.

After disabling auto-level the same print was realized without problem but I wasn't able to determine when and how this problem occur. The first and third time it occurs at the beginning (less than 10 layers I guess), the second one occurs at layer 49 on 81 after about 3 hours.

I'm using RAMPS 1.4 with Arduino Mega 2560. I already successfully made lots of prints with my printer without problem. I'm using negative Z-probe height. The Z min endstop is also used as Z-probe.

Thanks for your help.


  • What type of printer is - delta or cartesian?
    If delta have you enabled distortion correction (z correction)? This is the only autoleveling feature that can change z heights, also I had no problems with it so far.
  • It's a cartesian printer.
    The start script uses G32 S0 after G28 Z0 and G1 Z2.
  • Strange, also I use G32 S2 so I do not need to repeat autoleveling, there is no way that the formula starts to tretch z axis. It is always a linear matrix operation so transfomed coords are always scaled the same and I haven't seen this in my cartesian printer so far.

    Are you already using 0.92? It has some improvements for autoleveling.
  • Yes, I'm using 0.92 so I can use negative Z-probe.
    My problem is I can't (or don't know how to) get full log since print start with Windows Host to check what exactly was sent to printer and compare with real Z height. The idea is to add commands to G-code to get current Z from firmware at different places.
    I doubt it's a hardware problem, I made other long and high prints without problem with auto-level disabled.
  • You can enable logging in preferences->basic settings. It will create a file repetier.log in your work directory (reachable from file->work directory).

    One difference with autoleveling is, is that z is constantly moving during print. If you loose steps while doing so or if printer has z backlash the layer height will vary. Normally z moves only slowly so no big jerk and acceleration and also no problem. But as a test you can reset autolevel matrix (M322) and enable autoleveling (M320) so your print is identical as without autoleveling but without these z moves and still autoleveling routines/transformations enabled.
  • I have to measure the Z backlash, you're certainly right it might be the cause.

    Thanks for your help.
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