First of all, I'm quite new to 3D printing. After printing some temperature towers, stringing and bridging tests, I wanted to print the Bechys to see everything working together. I'm getting some strange "bumps" in the outer walls. It looks like for 2-3 layers, the filament gets lifted up.

infill before walls set

infill before walls unset

I first thought, the infill is printed too far in the outer shell, so I unchecked "Infill Before Walls" in Cura. Surprisingly the outcome did not change and the "bumps" where in the exact same spots as before.

I am aware of a part cooling problem, but my stock cooler already sits at 100 %. I don't think, the extruder temperature is too hot, with it being only 200 °C. As you can see, the printer only has a one sided cooling solution with a very small fan conduct.

fan conduct

Print settings:

  • Printer: Anycubic I3 Mega S
  • Slicer: Cura
  • Material: PLA
  • Extruder Temp: 200 °C
  • Bed Temp: 60 °C
  • Print speed: 45 mm/s
  • Travel speed: 100mm/s
  • Layer height: 0.2 mm
  • Layer width: 0.4 mm
  • Nozzle: 0.4 mm
  • Infill: 10 %
  • Retraction distance: 4.5 mm
    Retraction speed: 40 mm/s

So I am suspecting it must have something to do with the way, it is sliced. Does anyone have an idea?

Update: I started the print again with aligned seams. Now you can clearly see the artifact. At the point of the seam the print is warped inwards and upwards.

aligned seams

I did some more prints and tried to increase retraction distance up to 10mm and retraction speed up to 60mm/s, but I also did not manage to improve the print. I also tried to enable the "retract at layer change" option and to disable "Z Hop When Retracted" but without success.

I set the travel speed down to 45mm/s with no change in print quality.

  • $\begingroup$ Please slice with layer change aligned and post an image (20 layers should suffice), so that we can see if this is related to layer changes or not. $\endgroup$ – Davo Jun 18 at 16:37
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    $\begingroup$ Hi welcome to 3DPrinting.SE! What can be seen on the bottom photo is that your nozzle is a little too far from the bed, and you aren't using enough part cooling (see the overhanging bow). $\endgroup$ – 0scar Jun 18 at 22:00
  • $\begingroup$ @0scar I am aware of the part cooling but it already sits at a 100 %. I think I will do an upgrade shortly. I have already done a temperature tower, bridging and stringing tests. The benchy was just to see everything together. How did you determine, the bed being to far away from the nozzle? $\endgroup$ – mrei Jun 19 at 7:11
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    $\begingroup$ If the fan is already at 100 %, then you print too hot or the cooling fan doesn't provide enough flow, many print fan ducts constrict airflow, we cannot see what you are using. Your first layer doesn't look that well, there are many channels, but it is hard to tell from the photo. Sometimes 200 °C is just too hot, most PLA can be printed from 185 °C. The last photo looks as if the nozzle has overpressure at the end of the outer wall or oozed out filament at the start of the outer wall.This could be a retraction issue. $\endgroup$ – 0scar Jun 19 at 8:01
  • $\begingroup$ Thanks for the help so far. I'm going to play around with the retraction again and see if that helps. $\endgroup$ – mrei Jun 19 at 10:47

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