Filament gets bent and stuck in the extruder when ejecting
I originally posted this in the straight MK3s forum but was suggested I move it here since it may be (almost certainly is) MMU related.
After a print has finished (or failed and I hit stop) and it goes to eject the filament, there's about an 80% chance that the filament will get stuck.
It's not jamming in the hotend, it's getting stuck at the extruder gear. I've attached some pictures of the inside of the extruder (after removing the filament sensor) to demonstrate what I mean. I also just took some videos with some masking tape as a metric and what I found was that, at the end of a print, it pulls the filament out a couple cm, pushes it back in, and then pulls it back about 8cm. When everything works, this initial 8cm ejection is followed by a brief pause and then full ejection. When it doesn't work (which is frequent), it's only able to pull another half cm or so before that bend in the filament gets stuck and the MMU starts grinding.
8cm is about the distance from tip to extruder gear. My hypothesis is that the tip of plastic is still too warm when it ejects, and when the soft tip gets to the extruder it just causes it to warp into this hook I keep seeing which is then too big to be pulled out, but since it appears to happen entirely automatically on an M702 (or when I cancel the print) I don't know how to go about testing this, or how I'd fix it. Interestingly enough, it doesn't happen on a Tx command; I can run multimaterial prints with no problem, but then at the end there's about an 80% chance it can't make the final eject.
Has anyone else experienced this before? It wasn't always a problem, I remember making many prints without issue a few years ago. I can't recall when it started though. Is there a setting I'm not seeing that's, like, "wait X seconds after ramming before ejecting"?
RE: Filament gets bent and stuck in the extruder when ejecting
I was right. After some gcode experiments I figured out the filament was still a little soft as it was ejecting. As part of my experiments I also noticed that a lot of my filament was massively stringing as it was ejecting. Long story short, wet filament. I opened a fresh vacuum sealed spool and it's printing and ejecting with no problems. I thought I'd been doing well keeping them in sealed containers but it's been a moist summer, which explains why it seemed to "suddenly" just start happening, and has been getting worse.
RE: Filament gets bent and stuck in the extruder when ejecting
Thank you for posting. I have a roll of PLA that is doing the exact same thing. Was driving me crazy. I also thought it was coming out of the hot end too hot but could not figure out why it is just one particular roll of filament. I will toss it in the drying and see what happens.