Strange artefact on outer wall (solved -> under extrusion)

[sebastianha]

I am currently printing the Hula feets (Hula Feet Sovol Zero Remix (3MF Plug-and-Print) by Barry | Download free STL model | Printables.com) and I noticed strange artefacts on the side, exactly after the “HULA” on the outer wall:

I checked speed and flow in the slicer but there it nothing interesting:

I also tried to print without pressure advance but this did not change anything.

Does anyone have an idea what the reason for these artefacts could be?

Note: I did not use the predefined slicer settings from the 3mf, but my “normal” ones which worked fine on other models.

[cardoc]

Classic ringing. The sharp turns at the boundary of the letter excites printer resonance.

Try:

1. Check belt tension
2. Lower acceleration
3. Adjust “square corner” speed.
4. Rotate the model on the print bed

[sebastianha]

I will try, thanks for the answer. Never had this before.
Is there a guide somewhere how to tension the belts of the Sovol Zero correctly?

[sebastianha]

Findings:

• Ringing appears on both, X and Y axsis, so at least it’s not axis dependent. Also rotating by 45° does not help.
• Massively lowering the speed (to 50mm/s) produces perfect results (but that’s not the reason why I bought a Sovol Zero )
• Halfing acceleration (5000mm/s^s) did not help. Even lowering it down to 1000mm/^s still produces the artifacts.

I am not sure about “square corner speed” it’s on default and for what I have read the default should be good enough and not the reason.
Update: I lowered it to 3.0 but still getting artifacts.

This is leaving belt tension as last thing I can change but I am not sure how to set this properly.

[sebastianha]

I think I found it: It was under extrusion! I think somehow the PTFE tube was causing too much friction. I also tightened the extruder tension screw a bit and now it prints fine. I also lowered the max volumetric speed in the filament profile.

[HandyDoodads]

I replaced the stock PTFE tubing with a low friction variety that has a slightly over sized inner diameter. After replacing it I had significantly better printing performance with flexible filaments and one of my fiber filled filaments. The new tubing also is much more translucent which is nice when doing filament changes.

[sebastianha]

Digging deeper into this topic: It always happens when there are rapid speed changes and I think pressure advance cannot keep up to compensate this or the extruder cannot extrude as much as needed.

Example: With “Slow down for overhangs” here is a rapid speed change:

Exactly at the right part of the arc there are these artefacts. Of I can turn off “Slow down for overhangs” which solves the issue:

But that’s bad for overhangs. There is a relatively new setting called “Extrusion rate smoothing” which also helps:

But for me it only solves the problem if set to a relatively low value, e.g. 50

Perhaps I just have “bad” PETG?

[cardoc]

@sebastianha

Perhaps I just have “bad” PETG?

Is your filament 100% absolutely dry?

As the filament feed rate slows, hydraulic pressure in the melt zone drops, steam expands.

As the filament feed rate increases, hydraulic pressure in the melt zone increases, steam contracts.

Effectively moisture = negative pressure advance.

I never considered it but I suppose it is possible the filament could contain small amounts of volatile chemicals that vaporize at print temperature causing the same effect. What DO the manufacturers add to “high speed” filaments to lower the viscosity of the melted plastic? High speed filament could be exceptionally sensitive to temperature if some component chemical is on the cusp of vaporization.

Klipper’s square corner velocity is another “knob” to turn to help overcome this effect.

[sebastianha]

My filament is freshly dried, that is not the problem.

I again calibrated my pressure advanced especially for this filament, and that helped a lot! I think now the value is too high, but I will experiment further with it.