#[Klipper] Enabling Bed Mesh Levelling Squishes Dense Parts

1 messages · Page 1 of 1 (latest)

next drift
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Problem:
Parts that are dense or have a lot of moves in one layer seem to get compressed vertically when using ABL. When the part is done it looks squished, and the toolhead is a lot lower than the software thinks it is. For the cubes shown, it's about 4 mm lower than the firmware thinks it is. Turning off bed mesh levelling makes the issue go away completely, but I unfortunately need this for large parts. To confirm, usually I get flawless prints but this issue has arisen on models which linger on a single layer for a long time. Large plates or small dense objects seem to be affected.

Things I've tried:
checking extrusion factor - single-walled cube is spot on
different parts of bed - same issue on larger parts
tramming bed
tramming x gantry - it does this at the start of each print
creating a new bed mesh - it does this at the start of each print after heating the bed
reassembling the z axis
updating klipper
turning off perimeter overlap - at 0% for all tests below
adjusting start and end fade in Klipper Config

Hardware:
this is on an ender 3 pro V2 with bl touch, microswiss DD, rpi 3 with BTT SKR Pico, and dual z axis motors. The bushings are free in x/y but very little slack in z. I've also tried tightening them

Test prints (see number of dots on images):

  1. PASS no bed mesh, perimeter only
  2. PASS Bed mesh, start 1 end 0 perimeter only
  3. PASS Bed mesh, start 1 end 10 perimeter only
  4. FAIL Bed mesh, start 1 end 0 80% infill no overlap
  5. PASS No bed mesh, 80% infill no overlap
  6. FAIL Bed mesh, start 1 end 10 80% infill no overlap (cancelled at about 57%)
  7. FAIL Bed mesh, start 1 end 100 80% infill no overlap (cancelled at about 15%)
  8. FAIL Bed mesh, start 100 end 200 80% infill no overlap (cancelled at about 58%)
  9. FAIL Same as 8 but with bushings tightened. Cancelled at about 50%

More info below 🙂

signal-2024-01-30-194958_002.jpeg
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Hypothesis:
I'm pretty sure this is due to the gantry moving down a little more than it moves up when doing the adjustments as per the bed mesh. This might be caused by:
A) some mechanical issue that appears when the gantry moves up and down by small amounts continously
B) some software bug in klipper that causes it to drift over time when moving up and down by small amounts

I am at a complete loss so any help would be very much appreciated!

Attached are models and logs and config

📎 config-20240130-174128.zip 📎 klippy.7z 📎 dense_box.3mf
broken zinc
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Hi. Just to let you know that this is a Voron-specific Discord, not a general Klipper one. For questions about klipper on other printers, I would suggest the Klipper discord.

next drift
# broken zinc Hi. Just to let you know that this is a Voron-specific Discord, not a general Kl...

Thank you. I'm aware but was desperate and figured this wasn't machine-specific

I've solved this by disabling stealthchop on the z axis. I think the constant torque in the z- direction meant it was more likely to skip steps when moving up. On layers with a lot of extrusion length this was more likely to happen. Hence the denser/larger the part the more squished it was. No idea whether it was skipping whole steps or microsteps but spreadcydle seems to work for the test models so I'm happy.

broken zinc