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enter image description here

When I print the gcode repeatly, under extrusion happens at the same place.

The under extrusion not only occurs on first layer. I noticed the second layer also has some part under extruded, but not at the same place as first layer, because the infill line direction is rotated 90 degrees.

I have tried the following but could not solve the problem:

  1. Delta calibration (leveling)
  2. z=0 gap adjustment
  3. Filament flow calibration

It's a delta printer running Marlin 2.1. Slice with SuperSlicer.

The top layer doesn't seem to have under extrusion. There is even a bit over extrusion at the corner.

enter image description here

aleung
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    It looks like you came across a solution. It is preferred that "answers" to questions be posted separately so future readers can find the solution. Please [edit] your question to remove the "answer". – agarza Feb 09 '23 at 14:19
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    Please remove your last edit and post this as an answer! You can refer to the answer that helped you solve the problem (and leave that the accepted answer). Thanks! – 0scar Feb 09 '23 at 20:38

2 Answers2

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The most likely cause is that your bed just isn't flat. At least as I understand it, delta calibration is not mesh leveling, and is not there to correct for a non-flat bed, just for skew from the bed not being square with the towers or possibly other errors in the tower configuration.

Without knowing more about your printer, it's hard to know if you could add mesh leveling, but it's really a tradeoff anyway. You may be better to just adjust your Z offset so that the low points are sufficiently extruded, leaving the high points slightly overextruded.

R.. GitHub STOP HELPING ICE
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    Interesting read: https://www.klipper3d.org/Delta_Calibrate.html Delta calibration is not equivalent to Bed mesh, it is performed prior, so, non-flat build surface is therefor very likely! – 0scar Oct 10 '22 at 11:19
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    I had tried several solutions after asking this question. Now I can't tell how I exactly fixed it. But the most likely reason is that the bed wasn't flat -- I replaced the coated glass bed with a plain glass. Presumably the coating became uneven after cleaning and wiping. – aleung Feb 13 '23 at 05:47
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low-spots in the bed

If the bed is lower in some areas, the line is not squished there and more rounded. As a result, a line appears to be "under extruded"

High-spots in the bed

In other areas, the bed might be too high and block the nozzle - the line looks under extruded because it is too thin.

Uneven filament

When filament is uneven and below nominal diameter, those areas create a real under extrusion in the area when that area is fed.

Trish
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