I’ve looked around the CAD drawings and the forums, but haven’t found anything referring to what I’ve run into. So here goes:
I recently hit the end of a spool of PETG that was printing very nicely. I actually ran out of filament near the end of a print (gambled, lost), so I cancelled the print and tried to pull out the filament stub (which was below the hobbed gear, so the extruder couldn’t grip it anymore). And the stub broke off down inside the extruder body(!). Well, no big deal, I could just push it through with the front end of the next filament.
And that’s where I got stuck – literally. No matter how much force I applied, I COULD NOT push that remaining filament through. Thinking I had a hot-end clog, I ran (very carefully) a 0.3mm end mill up through the nozzle orifice as far as it would go – no blockage. I then tried a length of 28-gauge wire – same result. Judging by the length I was able to push through before hitting a roadblock, whatever the blockage was was above the hot end.
So, I just finished pulling the entire extruder apart. And It took quite a bit of force to remove the hot end from the extruder body. Once I got them apart, I discovered the culprit: I white (PTFE?) tube inside the extruder body, between the extruder gearing and the hot end. This tube had somehow shrunk around the filament and had it in a literal death grip (there’s about 10mm of “stub” sticking out the top of the hot end, which was what I was fighting during disassembly). The hot end, as far as I can tell, is fine. Thinking it might have been some heat creep, I cut a fresh piece of filament and tried to poke it through this tube – no way. And the stub of PETG sticking out of the top of the hot end, which was what was jammed inside the tube, still measures just under 3mm. So heat-creep induced swelling seems unlikely.
Thing is, I can’t find any reference to any PTFE(?) tubing being used in the Mini extruder in the documentation, the design drawings, or the forums. So I’m wondering what this tube is, and where it came from.
Looking at this extruder (I’ve attached a photo), I wonder if I got a lemon – this was a replacement tool head I bought from Lulzbot after my original hot end got damaged from running LayWood and LayBrick filament through it (back before I new any better). It ran three full spools of filament without any issue before this happened, but if you examine the photo. you’ll see that the tube end looks pretty rough, the green gears are not very well printed, and the body has a split through one of the hot-end mounting holes (it was there before I started disassembling the extruder).
Still, it’s well past warranty, so I’m not really interested in trying to pin blame at this date. I’m more interested in what this tube is, and if this is a normal but undocumented part of the Mini Extruder, and if anyone else has ever seen this happen before. There doesn’t seem to be any way to remove this tube, so can I try fixing it (run a 3mm drill through it?), or would I have to buy another toolhead (again! )?