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! )?
No, this is (supposed to be) a straight “regular” Mini extruder. And there’s no tube up at the top of the channel, or any reduced air gap between the extruder gears and the “entry hole.”
I’ve never printed any filament in that color, though.
Plus, the white “tube” feels too rubbery to be hardened PLA or PETG, which are the only materials I’ve run through this extruder.
If whatever it is had been there for any length of time you would not have been able print anything with it like you can not now. So it must be something that got pulled into the extruder. If this was a Taz I would think the end of the PTFE guide tube got pulled into the top of the block, but a Mini does not use any PTFE guide tube.
On the zoomed in picture it definitely looks like it was deposited in a melted state. There is some blue stuff there too. It’s the wrong color to be thread lock, and there’s too much of it. Can we see the rest of the extruder, including the top of the hotend? My only other theory is you ended up with one of the rare bowden style hexagons that did have a short ptfe tube in them, but which there should have been precisely zero of at Lulzbot hq. Seeing the hotend top will tell us more. Also I’d be concerned your cooling fan is nonfunctional.
I’m pretty sure my fans were functioning properly – I never saw any symptoms of heat creep, and the “stub” of PETG still sticking out of the hot end (see photos) measures out at exactly 2.85mm. So if heat creep were my problem, I would expect that stub to have swelled up – remember, that stub is what was “jammed” in the extruder body.
Weird. It’s not PTFE, AFAICT. Too rubbery and rough textured. Also a bit sticky. Not PLA or PETG either, though, – again, too rubbery, even at room temperature. About .25" long. That bit of blue looks like it could have come from one of my previous filaments, but that color was two+ spools ago. Is slight fibrous when cut with a knife. I honestly cannot figure out what it is, where it came from, or how it got down into my extruder. But the extruder exit hole looks perfectly fine with the white material removed, so I can only assume that this was foreign material of some kind. Weird…
Anyway, I’m going to re-assemble my extruder and see what happens.
That seems like the best contender – some sort of gummy label/sticker that got carried down into the extruder and only scraped off once it hit the closer-toleranced hole at the top of the hot end assembly.
Extruder seems to be working fine at the moment. My current problem is that, for whatever reason, I’m not getting any “squish” of the initial layer against the bed, even though the 4-pt bed calibration appears to be working perfectly fine.
(also, my hot end seems loose in the extruder body – it’s good in X,Y, and Z, but it’s able to rotate around Z. Is that normal? There’s no way to eliminate the rotational looseness – the mounting screws are already as tight as I can make them without cracking the extruder body)
It’s not ideal that it rotates, but it’s not unknown either. Usually the stock ones don’t though. it’s generally a symptom of underextrusion when the extruder body was printed. You can fix it by printing a thin ABS spacer washer and glueing it in to the underside of the extruder body above the hexagon barrel where it sockets into the extruder using Plastruct plastic weld or acetone (or hobby model glue). 0.5mm thick should be fine. Just make sure you keep the fillament hole itself clear of obstruction.
The other extrusion issue where it isn’t making good contact with the bed, you just need to adjust your starting Z offset. Also you may be underextruing slightly so running a fillament calibration test on the extruder is not a bad idea. Also make sure the fillament diameter is set correctly in Cura (the default 2.85mm may not be what your fillament actually measures with calipers)
Yeah, I had to spend some time making the M851 offset more negative. Had to change it by nearly 0.3mm, which seems odd – it was fine before, and even if the extruder mount change a bit due to my taking it off/on, you’d think that the bed levelling sequence would compensate for it. Oh, well.
(filament diameter is exactly what it should be, according to my calipers).
Your first picture shows your extruder body is cracked on the left side. I see the crack running between the layers between the bolt/nut and the edge of the block. So you might want to print a new body.
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