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[Solved] Overextrusion on random layers  

Overextrusion on random layers

Hi! This is my first post about the MK3S I built 5 years ago. Just stating that as a testament for how solid these machines are 🤗

As of recently (I suspect since my printer got clogged while printing with Arnitel: a flexible material) my prints contain very pronounced ridges on rand0m layers. I went and removed the PTFE tube from the hotend (didn't notice anything weird about it), pierced the 0.6mm nozzle with a needle until I could see through it with a flashlight (the inside seemed pretty smooth), inserted a new PTFE tube and ran the calibration process again.

Nothing has changed. This is a picture of a print I did directly after. It is a simple 25x25x25mm cylinder with the 0.3mm QUALITY preset in PrusaSlicer 2.7.4, printed in PLA.

As you can see the print quality is pretty impeccable, except for... well that's probably obvious 😅 There seems to be something weird going on with the flow rate, as if it gets blocked incidentally and then releases the pressure in one big swoop. The frequency and z-height of this happening changes from print to print, so is not g-code related.

Even after the new PTFE tube, cold pulls give this very weird geometry, where a main strand "blossoms" from the embrace of another strand, like the stem of a flower:

To me it seems like the filament somehow leaks out to a channel surrounding the central hole, but I'm quite puzzled as to how that would be possible or how to proceed. Any helpful ideas would be greatly appreciated!


Posted : 20/04/2024 11:24 pm
Illustrious Member

That looks like varying extruder pressure combined with a partial/intermittent clog ...

And is the collet gripping your PTFE tube properly?

Release the extruder idler pressure.  Heat to the hotter of your regular filament and PLA melt temperatures.

Take half a meter of PLA and manually push it down through the hotend, slowly first then accellerate to as fast as it will go - finish by pulling it out fast.

Retension the extruder idler, reload your flexible filament at the higher temperature, extrude extra (colour correct? No), go to working temperature and try printing again.


Posted : 21/04/2024 6:01 pm
soimon liked
Topic starter answered:
RE: Overextrusion on random layers

Thanks for your suggestions! It turned out either the heaterblock or the nozzle got loose during the cleaning of the dreaded filament blob. This created a channel where the filament could flow, harden and get stuck, preventing clean atomic pulls. Heating it up to the hottest temperature and then tightening the heaterblock and nozzle solved the problem: when I pushed white filament through it afterwards it contained a lot of black contamination that had built up and wouldn't get out earlier.

Posted : 22/04/2024 1:50 pm