TPU underextruding for a few layers

[grave willow]

The first half of my print went fine, but a few times overnight it started underextruding for several layers before recovering. I've used the same settings for a different roll of Ninjaflex without issue, but this print is more than twice as long as any other TPU print I've done.

Prusa Mk3S w/ Revo + ObXidian 0.4mm, sculpted PTFE https://www.thingiverse.com/thing:3819794/files
Ninjaflex white
245C, max volumetric speed 1.2mm^3/s
Brand new roll, dried at 130F for 6h

[edgy sinew]

AI Help

It sounds like you may be experiencing issues due to the length of the print and the characteristics of the TPU material. TPU can be more prone to issues like underextrusion, especially on longer prints. Here are a few troubleshooting steps you can try:

1. Check the filament path for any obstructions or tangles that could be causing intermittent underextrusion.
2. Double-check your nozzle and hotend for any signs of wear or clogs that could be affecting filament flow.
3. Try reducing the print speed slightly to see if that helps with consistent extrusion over longer periods.
4. Check if the extruder gear is gripping the filament properly and not slipping during the print.

Since you've had success with a different roll of Ninjaflex, it's possible that this specific roll may have slightly different properties that are affecting the print. If the issue persists, you may want to try a different roll or batch of filament to see if that resolves the problem.

WARNING: This response is AI generated and may contain errors.

[rotund berry]

check the extrusion tension, it might be over squishing, just tighten and loosen the screw while it prints and see if anyhting changes

[grave willow]

The screw is about 1mm from the surface with the filament loaded. (For regular filaments, Prusa recommends the screw be flush with the filament unloaded)
If the tension is off enough to underextrude like that, wouldn't it be more consistently bad? I checked several times and the walls looked like they were extruding the correct amount. (touching each other without getting pushed past where they should be)

[rotund berry]

actually if its under extruding for many layers i think it might be a jam or partial clog, might need to fine tune retraction settings to be lower or even off

[rotund berry]

just afraid that the spool might not be consistant enough, which a thinner or thicker section of filament can be jammed into the extruder gears

[edgy sinew]

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[grave willow]

I had a chance to run this again with speed (1.2mm^3/s to 1.15) and retraction (2.5mm to 1.5) reduced, and it did the same thing starting at about 12h in.
This time I was able to catch it pretty quickly and send M600 which usually fixed it for a bit. Around 3/4 through this stopped being effective so I tried pushing some PLA through which resolved the issue for the rest of the print.
I did notice the end of the filament was flat every time it was unloaded with M600 which seemed strange, does that tell you anything?
I also felt like there was some resistance higher up when I manually pushed the PLA in, followed by a bit lower resistance and finally higher when it started extruding. I'm guessing this could be the filament getting slightly caught on the transition from the heatsink to the nozzle threads, hitting something that got pulled up during unload, or hitting something that got pushed up during printing. Thoughts?