Need help troubleshooting extrusion that gets stuck
I have a MK3S that I've got a lot of good use out of (the stats say 180 days of print time). Recently, it's developed a problem where it just stops extruding partway through prints - the other axes keep moving along, but nothing is coming out of the nozzle (or at most, a tiny bit of stringing.) It starts out great, I get a beautiful first layer, then at some point often around half an hour or so in (though the timing is not consistent), it stops extruding and doesn't start again. I can usually (though not 100% of the time) unload the filament normally. After clipping off the chewed-up part where the gears have been trying to push it, it loads again just fine. After reading the Prusa manuals, searching through this forum, etc. I've tried a bunch of things and I'm running out of ideas. Here's what I've tried:
- Adjusted idler tension, all the way from just barely catching on the nut, up to levels that are clearly too tight, and everywhere in between. When the idler is on the loose side, the extrusion just stops silently. When it's tighter, I get the telltale clicking.
- Tried several different filaments (mostly PLA) from different brands including Prusament. Tried some brand new spools as well as some older ones that have worked fine in the past.
- Checked bondtech gear alignment and cleaned out plastic debris on the "teeth" from previous failures.
- Tried three different nozzles (0.40), all genuine E3D ones that have worked fine before, and have tried cleaning them with acupuncture needles and nylon cold-pulls (one is brass, one is hardened steel, and the other is the E3D "Nozzle-X", which is what I usually print with).
- Re-calibrated PID in case the temperature wasn't staying steady enough or something.
- Completely disassembled my hotend, so that I could get a good look inside the heatbreak, etc. to look for obstructions and so that I could make sure everything was still tightened properly when I re-assembled it. Didn't find anything, and could feed filament through by hand just fine. Replaced the PTFE tube with a fresh one while I was in there.
I'm running out of things to try here - can anyone suggest where to look next?
Out of curiosity, does your heater block wiggle from side to side when pressure is applied to it from the side while it is heated. Also does filament curl up immediately after exiting the nozzle when extrusion is working properly? I had an extrusion issue very similar to what you described and I’m curious if your hotend has the same issue.
Good questions @almostsheldonpk! When I started this whole thing, the heater block would indeed rotate when pressure was applied. After tightening down the screws that hold the 'C3' part that holds the heatsink in place, it no longer does this. And, when I first load, the tip of the extruded plastic gets stuck on the nozzle, so I get kind of a big 'loop' descending. where one end is stuck to to the nozzle and the other is extruding, extending the loop until there's enough weight to detach it, then it extrudes straight down. Does this match what happened to you?
Thanks for the in depth response,
My hotend also had the rotational movement. I didn’t know that tightening c3 would fix that. Thanks for the tip. But in addition to the rotation there was a lateral non rotational movement of the heat break and heater block that made me suspect that the hotend might have became damaged.
Regarding the curling of the filament, it matches pretty closely, in my case it was cyclical though. Every time the filament built up enough weight to drop it curled up again and repeated in that cycle. After I replaced the hotend that behavior ceased almost entirely.
Yeah, I could definitely consider replacing the hotend, though this one is not all that old. I had to replace it a few months ago when a failed print encased the whole heater block in a blob of plastic, breaking the thermistor and heater cartridge wires when I tried to remove it, so I just decided to replace the whole thing. I also wonder about the E-axis stepper motor, though there's not obviously anything wrong with it and I'm not sure what I could test short of just replacing it.
This is probably not worth the effort, but assuming you still have your previous hot-end, you could remove it’s heatbreak and swap it into the current hotend because it sounds like the only part of the filament path hasn’t been replaced is the heatbreak.
Good luck with whatever you chose to do