donmilne

I find the first article a bit anecdotal, and I wonder if the low quality of the prints accelerated their degradation: all that dirt and moisture being trapped in the "grain". The second article however I find very interesting. It seems to be saying that the claimed biodegradability of PLA is largely hype. I can believe that the colored dye might get bleached relatively quickly if not protected from UV, but it would be interesting to know what the effect is on mechanical aspects: brittleness etc. I'm especially interested in objects that are not buried in the ground!

What is the purpose of the option? Is it to fix non-watertight models? So I shouldn't need it if I use a decent modeler?

Yes, that was it, well done and thank you. Here's the new nut added to the original bolt. I'm not sure how that "Fix Horrible" option got set. Score one more for TrevM's thread library. Unfortunately the external size of the nut and the head of the bolt don't match what I expect for metric fasteners, but that should be easily fixed. Still, the threaded part is near perfect and it's all a huge step up from the other libs I tried that didn't work at all.

Hmm. I didn't expect that PLA would sag over time - it doesn't seem to go with being brittle. Thanks for that tip. I'm also surprised that ABS might fade, I know that external switch boxes etc are often made of ABS so I guess I assumed all ABS is like that. Is there a specific clear UV coating that is recommended?

I read that PLA is biodegradeable - a statement that makes me want to shop for a roll of ABS. But, before I go too far overboard... does anybody have numbers on how well PLA stands up to weather: rain, cold, strong sunlight etc? Of course, I happily make things out of wood, which is also a biodegradable material, which also has a tendency to warp, shrink or swell if not protected. You would typically protect wood by regularly painting it - ideally with an oil based paint. How well can PLA be expected to hold up in outdoor applications?

For some time I've been meaning to have a go at printing real metric threads, to see how well it worked. I'm designing in OpenSCAD and I've tried the internal threading library and a couple of others, without much success - I get loads of warnings in OpenSCAD - and what seems to be a total lockup, though maybe I just didn't wait long enough. That's just for background, I'm not looking for OpenSCAD support here. Anyhoo, I came across an "ISO metric thread library" on Thingiverse, by "TrevM", and it has been much more successful. See below for a result of a quick test of printing a hex nut and bolt. Points to note: These are an M10 nut and bolt. The inset picture is the same hex nut flipped over to let you see the underside. The bolt is particularly successful, nice clean realistic looking threads. So realistic in fact that that's a real steel M10 nut you see screwed onto it. There's a teeny bit of play in the nut, but perhaps I could fix that with tuning. The hex nut is... not so successful. It went great until z=1mm (approx - I suspect it's the 1.2mm shell thickness I set), at which point I saw what looked like stray hairs crossing the hole, however when I came back an hour later it looks like a solid plug filling the hole (top right of pic). Support was turned off. The nut looks ok in Cura and other views prior to slicing. Cura was the slicer btw. Nut and bolt were printed at the same time. I tried to fool the site into letting me upload a zip file containing the project files, but I couldn't see a way to link it to this message. I can email it to anyone interested if they pm me an email address (offer valid for a couple of days only!). Alternatively, suggest a way to attach a zip.

Were you printing both at the same time?

Just for completeness: I've seen the third fan now (I actually find it more visible looking at the rear of the printhead), and yes it is still working fine.

Thanks for that very clear answer.

Ah, right. Now that you mention it I do remember seeing that. Changed it how and where? I could hardly forget using the Tune menu, and you said above that a new print with Cura would reset the temperature back to default (*). If the temp sensor has failed after only two weeks then I'll not be best pleased. (*) Are you still sure about that? In the materials menu I see PLA, ABS and Custom. ISTM possible that non-default values could be stored in "Custom" and would apply until I explicitly selected PLA again from that menu.

No, I didn't check this. The circumstances of the original failure was given in my first post. It was a print that came loose from the bed and stuck to the nozzle, hence creating a blockage which I assume allowed heat to propagate back up the filament. Anyway I don't know what you mean by the "third head fan" - there are only 2 obvious fans on my UM2 printhead. I can hear what is probably a third fan somewhere, but I don't see it. Are you familiar with the UM2? I was careful to check here on how to remove and replace the Bowden tube before I tried it. I didn't simply yank it out and hope for the best. I did try your advice to loosen the print head screws before pushing in the tube and the retainer, but I can't say the grip on the tube seemed any firmer than doing it without that step. The print came loose because I made the mistake of trying a UM1 profile in KISSlicer, not realizing that it wouldn't include g-codes to heat up the bed.

"Tune menu"? I don't remember seeing one in the UM2. @IRobertl: Thanks for that. I'll keep an eye out tho. The cooldown display definitely showed 259C, but it's possibly just an approximate value.

You know it's weird, but I could swear that it's printing better than before. Can't think why, except that I reduced the temp to 220C and tweaked the support (moved it a tad further away).

I know that the temperature setting is now stored in the printer (UM2). However, if I use another slicer for one job - and this one overrides the temperature, then I use Cura for a second job, does the printer return to the default material temperature, or does it continue using the override? If I ask the printer, it shows me (say) the PLA profile - 220C, but I'm not convinced that was the temperature it was actually using, because the cooldown display showed ~260C, a temp I had set for a special print intended to clear a filament blockage.

Hooray! Filament feeder reassembled and bolted back in place (feeder motor too), material change went flawlessly and the printer is now printing again.... actually I just had to abort it because I forgot to enable support, but it looks like I'm up and running again, thanks for everyone's help.

Thanks for the advice on posting of images. Ok, if this works then it shows what the filament looks like. Wow, that was some rigmarole to post a picture. Thank heavens this site won't care much about how things look, right? As to the links to other discussions, they seemed to involve clearing a nozzle blockage and completely dismantling the print head - neither of which I thought I needed. I still don't.

Hindsight is wonderful, but how should one establish that in advance, and I wonder why no mention of this caveat in the manual?

Anyway, thanks to all for your advice, especially the advice on how to correctly remove the Bowden tube. Once I did that I found that the white bit could only be pushed down with difficulty, but once I did the filament did come out quite easily, everything looks clean inside. I'm glad I didn't have to disassemble the entire print head. On inspecting the business end of the filament the problem is obvious. I still don't know how to upload pictures so I'll have to describe it: the PLA has softened and created a nice little collar for itself around its entire diameter, about 8mm from the end of the filament (I would guess there must be a small (~1mm) gap between the end of the Bowden tube and whatever it butts up against). In my earlier mishaps described in my OP I assume the printhead has got too hot, the PLA has softened and filled that gap, then cooled again, and then it couldn't move. The collar is over 4mm at the widest, so there's no way that was ever going to reverse through the tube. I don't know what was stopping it going forward, I assume there's a similar constraint in that direction. I've replaced the tube now, I'll put the feeder back later on. I'm hopeful it will now work. I hope there's no trick to getting the tube back in place. I assume you push it in as far as it'll go, then push the white bit down and put the retaining clip back?

@gr5: the idea of printing PLA for at least 10 minutes at 260C in order to clear a print head blockage is the recommended procedure given in the current UM2 User Manual, "Troubleshooting" section.

Is there a diagram or parts list or tutorial that shows how the printhead comes apart?

Ok, I have the feeder disassembled and lying beside me in pieces on my desk. The filament is still in the printer and still stuck. Hopefully we can now all agree that the feeder is not the problem. I had a go at undoing the screws on the printhead. The stack all opened up concertina style, I can see that the filament doesn't go all the way through to the nozzle, but it still doesn't seem to want to withdraw.

When you say "extruder" I assume you're referring to what I call the feeder (IMHO the "extruder" is the hot end, where plastic changes shape). Luckily I had experience on day one of taking the feeder apart. That doesn't faze me, but nor, given my previous experience, do I believe that to be the problem this time.

I already checked the feeder, I mentioned it in my first post: there's a bit of dust in there, but it doesn't seem excessive. I have already given the filament as big a pull as I dared - this is what I referred to when I said that it wouldn't budge even with my assistance. I also tried loosening off the tension screw and tried the same thing again. I get about 5mm of movement in the filament, nothing more. Whether or not this is the cause, IMHO it would be useful to know how to take the print head apart, so I'd appreciate answers to the Qs in my last two posts?

I don't suppose there a slideshow of this anywhere?

Thanks for the quick reply. The Cura was set to 45mm/s, 230C. Shell thickness 1.2mm, 20% fill. I've had some good prints recently with these settings, if only the damn support structures wasn't so strong! Are you saying that if I undo the top four bolts then the major part of the print head (nozzle, fans etc) should pull off downwards? and I only need to avoid pulling the Bowden tube down with it?