Reasons for changing extrusion width in the same layer?

  • Hello all! 🙂

    I've got a weird problem which I noticed on several prints of my DIY printer: In the same layer the top surface has gaps AND very slight overextrusion.

    Reasons I've considered to be the cause for this:

    • Sponginess in the extruder.
      The area where the gaps are is the beginning of the infill pattern so that would make sense. On the other hand I use a Bondtech BMG as a direct extruder and PLA which is quite stiff which again makes the extruder an unlikely cause.
    • Some weird distortion of the gantry.
      I had this problem on a prior iteration of my printer where I had a quite stiff hose attached to the carriage which flexed the gantry beams (12 mm smooth rods) depending on the position of the print head. Since then I exchanged the hose for a much more flexible one; also the part is very small so even if the gantry were to be distorted the effect shouldn't be noticeable.
    • Uneven bed.
      My print bed is indeed not the straightest one (it's an IKEA mirror about 400x400 mm) but the part is very small compared to the global wonkiness of the bed and also this effect should even out after some layers above the bed.
    • You tell me 😬
      Are there any more reasons you can think of? I'm running out of ideas 🙄

    Thanks in advance! 🙂

  • I'd say the gaps are down to what the slicer is doing. Can you look at the individual layers in the slicer? If so, try varying the extrusion width and see if that helps.

  • @deckingman In the slicer (PrusaSlicer 2.1.0) the lines look consistent... I hope that the slicer does produce even extrusion commands but it's hard to judge looking at a bunch of numbers in the g-code

  • @Eumldeuml Just looking closely, there is a gap lower right of the "D" and also, looking closely, it looks like 3 perimeters but they don't touch fully - almost like you can see 3 individual beads. Try increasing the extrusion width. TBH, I'd say that's more like under extrusion than over extrusion apart from the slight blobs likely caused by not quite enough retraction or too slow a retraction speed.

  • @deckingman The extrusion preview in the slicer around the "D" does show the gap that is also visible in the picture I took. But my problem is the uneven extrusion on the outer "rim" of the part. In the bottom left there are gaps in the zig-zag pattern that aren't there in the top left corner...

  • @Eumldeuml I think I see what you mean. It looks rather like the top layer is more "squashed" on the right than it is on the left. Almost as if the part isn't level so you have a bigger gap between the top of the part and the nozzle on the left than on the right. Try printing it again but rotated 180 degrees on the build plate. If it still looks like gaps on the left, then it's a mechanical issue with your printer, rather than anything related to extrusion or slicer.

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