K2 Plus PETG Nozzle Buildup/Shedding Clumps of PETG on Build Plate

Flagship K Series Creality Flagship K2 Plus & CFS
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1

Hello there,

We recently got a K2 Plus with CFS just for printing functional parts out of black PETG. I’ve had several issues getting the system to print well including extruder jams, poor dimensional accuracy, print to print precision, and calibration issues. I’ve been able to solve all the above issues (mostly by switching filaments and doing extensive testing and calibration), but I have one remaining I cannot seem to solve: nozzle buildup leading to clumps of PETG shedding onto the build plate. If these clumps happen to fall on the prints, they often will bond enough and the print be ruined. The PETG on the nozzle also adheres to new layers while printing, messing up dimensional accuracy and print quality.

I’ve done everything I’m aware I can for this:

  • Removed the hot end and remounted, ensuring all screws are tight
  • Run Auto bed calibrations before every print (would prefer not to, but that’s where we’re at)
  • Calibrated z-offset So. Many. Times! (Settled on a value of .05mm. If set higher than that, my first layer is underextruded/comes out poor with gaps between lines)
  • Calibrated my filament’s temperature, pressure advance, flow ratio, and max volumetric speed)
    • Overture Black PETG, 250C, .13 PA, .92 FR, 11 mm3/s MVS
  • Enabled “Avoid crossing Walls”
  • Experimented with Z hop when retracting and disabling wipe while retracting, but this causes stringing issues and didn’t seem to help
  • Changed first layer height to .28mm, and others to .24mm (from default .2mm for both)

From what I can tell, this buildup seems to occur on layers 2-5. There is no build up after layer 1, and I’ll often pause after layer 5ish to clean the nozzle and any chunks (sometimes there are chunks, sometimes not, even if it’s the same item being printed. It’s weirdly inconsistent). If I do that, the print usually comes out great with minimal buildup after that.

I know PETG is sticky and there are non-stick treatments for nozzles and such, but I’d prefer not to go down that road, as that seems to be sidestepping the real issue. I print these same parts with my BL A1 with the same filament and similar settings, and I’ve never had any nozzle build up, ever.

I’m really hoping I’m missing something obvious. Does anyone have any ideas for me? Please and thank you!

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That build up on nozzle is often associated with the nozzle bulldozing the model. Check your infill / wall overlap. The programs (CP6) defaults to 30% (waiting for it to be fixed) but it should be 15%.

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Will try, thank you very much!

Will this lead to worse joining of the walls and infill/pinholes or will 15% still provide suitable fill for those transitions?

5

It will lead to standard joints as per Bambu and others.

If you hover on the infill it will advise 10 to 15% but they cocked up the programming defaults. It took me lots of the above to find what causes it, and if you happen to do a tall thin model then it will fall over 1 out of 5 prints.

Hope its the reason.

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Alrighty, after about 8 more prints, it seems this may have helped a bit, but didn’t completely eliminate the issue for me. I tired 15% “infill/wall overlap”, then 10%. I also changed the “Top/Bottom infill/wall overlap” from 25% to 15% to see if that helped, but it’s about the same.

After closer inspection, I’m seeing some buildup on the first layer will prints with very large bases. Interestingly, the accumulation only seems to happen on the right and rear-right part of the nozzle (from looking in the door), never on the left. Don’t know if that’s a helpful clue.

Any other ideas are greatly appreciated!