Blocked extruder

Help!! The filament got stuck in my extruder and I can't get it out!

This morning, I did a print. Started it, verified it was working ok, and then went out. Came home and found a good print, with the extruder back up at Z=0 and the fan running, like usual. It was idling like this after the print finished for about an hour, I guess. I turned off the whole printer when I got home. (The bed was already cold and the parts separated from the glass easily, so I know the gcode had run to completion.)

This evening, I tried to print. The extruder's big gear was turning, but the filament wasn't moving. And of course, no extruded plastic PLA was coming out.

So I started pulling on it in various ways to try to get it backed out. First slowly, with help from reversing the extruder, making sure to have the hotend at 220C, then pulling harder with pliers, etc. I disassembled the idler and found the hobbed bolt spinning against a hole in the filament (duh). When I finally got the filament unstuck by levering it out with two pliers, it was puffed up on the end to a diameter of easily 4.5 mm (from nominal 2.85). And then I noticed it had broken off and the rest was down in the printed bracket leading into the hotend. So I took the hotend off, and heard a crack, and found that the filament was stuck inside the printed bracket, and also in the hotend. Drilling out the stuck filament in the bracket was easy. Drilling into the filament in the hotend and putting a screw in it for pulling it was the next plan, but it didn't work too well.

Wondering two things.... (1) what I did (or what went wrong?) to make this happen, and (2) how to get the filament stuck in the hotend out.

Sorry if this is a FAQ, feel free to point me at a "hotend is blocked for noobs" document if it exists.

I've read the manual's advice about only pulling out the filament when hot, and that it will stretch and come out without leaving stuff behind.That's how I planned to get the filament out, except for the fact that my filament swelled to 4.5 mm and wedged in the hole leading to the hotend.

-jeff

I should say, I quickly searched and found an overwhelming array of advice on blocked extruders. The problem is that all the videos/blogs etc look different than the extruder in the Mendel90 kit, so I'm not too sure which advice is applicable (just needs to be adapted) and which is totally useless.

-jeff

Sounds like you had heat travelling up your insulator to the point where the filament softened at the input and bulged causing a jam. A fan on the insulator can help with this sort of problem.

Did the gcode turn the extruder off at the end? I have only heard of it jamming like that if it sits at temperature without extruding for a long time. Since it completed the print it must have been working until the end. It should then switch off so should have been fine to start a new print.

If you have a heat gun you can heat the cold end until the PLA becomes rubber like and then you can pull it out with pliers. You only need to clear the grub screw area. The rest in the PTFE liner should extrude if you heat it up to extrusion temperature and push it with some new filament or the blunt end of a 3mm drill.

Don't drill into it as PLA is harder than ABS and PTFE so the drill will wander into those and damage them, rather than remove the PLA.

Edited 1 time(s). Last edit at 03/16/2013 08:15PM by nophead.

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Thanks for the advice. I came the the same conclusion about the hotend staying hot for a long time, so I'll check the GCode and the actual behavior of the printer carefully on my next print to see if I can find the problem.

I ended up disassembling the hotend, separating the brass from the black plastic so that I could apply heat on the top while simultaneously pushing the filament backwards by pushing an Allen key back up from where the nozzle would be. I really hated taking it apart, but I had no other option, the way it was broken off flush. Luckily, when I put it all back together, it worked fine, without leaks.

I was applying the principle of "if it's jammed, force it, if it breaks it needed replacement anyway". I figured that breaking my hotend in order to learn how to not break it the next time would be an expensive lesson, but worth it. In the end, I didn't break anything! Happy day.

-jeff

heppended to me a few times as i did not always shut heater down while I should have...

best way to fix this I experimented was to heat extruder on/off as many times as needed until big "blobs" of plastic blows out. Just on/off 2/3 more times until no blob flow from hotend. You can then manually reverse extrude pretty easily