Filament getting stuck.

I’ve had the Taz 5 for a little over a week and I’ve loved it. It’s been very reliable and consistent up until last night. Filament suddenly jams on the slightest retraction. When it jams it not only won’t push further into the hotend, it won’t pull out without pliers either. Snipping the filament to a sharp point and feeding it back through fixes it, until I retract at all., then it jams again. I’ve had a similar problem on a cheaper printer when the PTFE became damaged, but to knowledge, the Hexagon doesn’t use PTFE. Hopefully this is a common and easily fixed problem? Any input is appreciated, thanks!

Printing Esun Pla at 205
With retraction at 20mm/s speed and 2mm distance. It’s been working just fine till last night.

My first thought is about the tension adjustment pressing the filament against the hobbed bolt. Is the spacing between the faces of the washers on each end of the springs in the range of 5 - 7 mm?

When you open the pressure roller, does the ball bearing that presses the filament against the hobbed bolt spin freely, in both directions? I had mine start jamming a while after I got my TAZ5, and it turned out to be what appeared to be plastic support debris left over from the support arms being printed, jamming between the bearing and its support arm.

Does the filament have a section chewed out of it, once you pull it out?

You might try cutting the retraction speed in half, as an experiment.

The tension started out kinda loose, it was one of the first things I checked. It is now around as tight as when I first go it, and 7 mm from washer to washer. The wheel opposite of the hobbled bolt spins freely in either direction. The filament does have a chewed out section from the hobbled bolt grinding away trying to shove the jammed filament downwards. Also, when it is jammed I have to apply upwards force with pliers just to pull out the filament.

I set retraction to .5mm and successfully completed an hour print, but I still don’t know why I suddenly can’t print on the retraction rate I had been using since I got the printer.

I noticed filament, even when clipped to a sharp point, will slide easily into the hole below the hobbled bolt up until it reaches the depth of where the plastic meets the metal platform at the top of the hexagon hotend. At that point it catches, and I have to apply extra downward force or lift it up and try again until it sinks into the hotend. Is that normal? I’m thinking maybe misaligned holes between the plastic and metal?

Inserting filament in mine works the same way.

I try to trim the end to a sort of sharp point, but usually end up having to rotate the filament around (by moving the flexible feed tube around) while pressing it in gently until it finally goes in the rest of the way and I can then push on it and see filament extruding out the nozzle.

I’ve also wondered if there’s not some sort of misalignment in there, and whether it affects the maximum extrude and retract speeds, but so far I haven’t taken things apart to check that. If you do check and find a problem there, please let us know.

I believe that the catch is actually a conscious design decision. The filament hole in the plastic portion of the extruder is slightly larger than the filament hole in the hot end to allow for mis-alignment between the two pieces. The machining tolerances achievable when manufacturing the metal hot end are much higher than the tolerances achievable with a 3D printer. If Lulzbot did not make the filament hole in the extruder larger it would be even more difficult to thread new filament in.

Hmm…That makes a lot of sense. Thanks!