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Marlin Autoleving Issues

Posted by Matt225588 
Marlin Autoleving Issues
January 19, 2021 11:22AM
Hi, have an Anet A8 that I swapped the Frame with metal extrusions. I have been working on this printer for about 2 years and I cannot get the auto bed leaving to work properly. I currently have a BL Touch see the reading on the bed attached. With just the G28 command I can print just fine; however, when I use G29 it seems like it is un-leveling the first layer. No matter how many times I relevel or even unlevel the bed the results are the same. The printer lays down one side of the bed too high and the other side too low. I have tried an inductive sensor as well but has the same effect. It seems like the printer is getting consistent readings. Does anyone have an idea what is going on? Thanks.
open | download - Photo Jan 17, 5 35 04 PM.png (773.7 KB)
Re: Marlin Autoleving Issues
January 19, 2021 12:17PM
What version of firmware do you have, newer versions have

Computer Programmer / Electronics Technician
Re: Marlin Autoleving Issues
January 19, 2021 12:30PM
I believe it's version 1.1.9. I was unable to get 2.0 to compile. I have enabled "#define RESTORE_LEVELING_AFTER_G28" but I had to disable it because it makes the first layer uneven.
Re: Marlin Autoleving Issues
January 19, 2021 03:43PM
With an Anet A8 (even one upgraded to a metal frame) there are two possible mechanical issues that could cause something like that.

The first is a twisted X axis - if the two rods the X axis moves on are not exactly parallel (it doesn't take much - 0.5mm difference from end to end is noticeable) and the Y probe offset is not 0, then the effective probe Z offset will change across the bed and the mesh will be higher on one side vs. the other.

The other is that due to the 8mm pitch lead screws it is very easy for any push on the X axis to make it unlevel. This can be worked around by printing out leveling blocks that you can use before each print (such as Anet A8/Prusa i3 - Z-Axis Alignment Tool) to ensure the axis is as level as possible. Other options are (if the control board and Marlin version are upgraded) using independent drivers for the two Z motors and enable Z_STEPPER_AUTO_ALIGN so you can use the G34 gcode to auto-align the X axis at the start of the print, or to add a belt connecting both Z motors so they don't get out of sync.

The upshot is that this is most probably a mechanical issue to be resolved, not a Marlin issue. I speak from experience - I saw the same sort of behavior with my Anet A8. On the left hand side the bottom rod was around 0.5mm behind the top rod, while on the right side they were even. This caused my mesh to always be higher on one side than the other. Even upgrading to the AM8 frame was insufficient to resolve the issue until I also implemented the BLV MGN12 upgrade which replaced the rods with a linear rail.
Re: Marlin Autoleving Issues
January 20, 2021 09:36AM
Thanks. I just checked the x axis and they where slightly off. I reprinted x axis holders and it is now perfect. I did a few test prints and it had no effect. I checked the y axis and it seems to be off quite a bit. The rails don’t appear to be level. It appears to be the metal extrusions need to be readjusted. I will adjust them and follow up.
Re: Marlin Autoleving Issues
January 20, 2021 05:12PM
I think that the bed leveling would handle the problems in your Y axis just fine. It's the X axis that generally results in the behavior you're seeing. It doesn't take much - 1/2mm between the rods at one end can result in over 0.5mm offset across the bed.
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