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Printer: SecKit Go w/ BMG/v6 and SKR v1.3/TMC2130 Drivers

Slicer: Simplify3d or Cura (problem is much worse in Cura?)

Long story short - after getting this printer running, I have noticed that it will underextrude ONLY on corners on an internal perimeter specifically once we're above bottom layers - and nowhere else. See below:

enter image description here

E-Steps have been calibrated, extrusion multiplier has been calibrated (single perimeters are 0.48 mm), linear advance has been calibrated, but here it gets weird. Anything resembling a 'standard' value (suggested between 1-2) results in MASSIVE underextrusion after the speed change. I was able to get a good looking line using the linear advance test with a value of 0.15 (which seems very low).

enter image description here

Retraction (1 mm @ 30 mm/s), junction deviation (0.02) and all other settings are off the factory Simplify3d profile. Turning linear advance off makes the problem slightly better but doesn't fix it, going to a value of around 1 results in huge underextrusion after any change in direction.

I am absolutely lost as to what to try next.

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  • $\begingroup$ I read that linear advance or junction deviation settings in firmware clash with Ultimaker Cura as it uses similar techniques in the slicer itself. $\endgroup$ – 0scar♦ Mar 9 '20 at 22:45
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I switched over to PrusaSlic3r and 99% of the issue went away even with copying settings straight over.

Maybe Cura/S3D handle internal walls differently?

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  • $\begingroup$ Thanks for posting an answer to your question! Please accept after 48 hours. $\endgroup$ – 0scar♦ Mar 9 '20 at 22:46
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From what I can find, the SecKit Go has a direct drive extruder, so 0.15 is a very reasonable linear advance K value. For comparison, I have 0.6 for PLA with a bowden. Values in the range 1-2 are way too high for direct drive except possibly for really soft TPU.

Geometrically localized underextrusion almost always means you have either

  • loss of material due to oozing elsewhere, or
  • filament slippage

usually due to whatever's being printed just before the part with the underextrusion. If it's oozing you may need to increase retraction or disable or limit combing in your slicer (to prevent unretracted moves; these can ooze a lot of material when crossing infill areas). If it's slippage it could be from trying to print too fast.

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  • $\begingroup$ I was under the impression that most direct drive extruders ended up with a value around 1 (the Titan clone I had before was 1.2).Happy to be wrong though. Although I have experience with multiple printers, 32 bit boards and 'fancy' stuff like this are new to me. You can see in the print that the underextrusion happens on multiple perimeters, when there is zero chance for any oozing to happen. These are printing at 75mm/s which is well within the capable speeds of the SecKit (many are printing +100mm/s), and even if I slow down further to ~50mm/s I get the same issue in the same places $\endgroup$ – Drew Spriggs Mar 4 '20 at 6:11
  • $\begingroup$ Are you aware that the units of K changed between Linear Advance 1.0 (older Marlin) and 1.5 (Marlin 2.0.x and 1.1.9)? See marlinfw.org/docs/features/lin_advance.html $\endgroup$ – R.. GitHub STOP HELPING ICE Mar 4 '20 at 6:34
  • $\begingroup$ That might be why I thought the figure was nonsense, but I now don't believe it's relevant to the issue I am having. Increasing it makes considerably more underextrusion in -different- places, but decreasing or turning it off doesn't improve the underextrusion on corners of inside-perimeters only. $\endgroup$ – Drew Spriggs Mar 4 '20 at 11:59

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