Help! Filament jamming problem

Hi all,

Been printing in ABS every day since Oct last year. I've had a few filament strippings in that time, and only ever needed to yank out the cooling filament from the J-head for "cleaning". Last week that method stopped working, the prints were constantly beading or stopping as the filament struggled to feed. I ended up dismantling and cleaning the nozzle for the first time, but on reassembly it would only feed for a couple of print layers then start stripping the filament. Trying to push the filament through by hand was near impossible. It used to be easy.

Anyway, I had this hot end from Poland that I'd been wanting to try. I put it in and printed a fantastic thin-walled cube before it jammed up. Hmm, two jams... ABS? Near end of successful reel, but anyway I changed to a different (new) spool of ABS, same problem, also near impossible to push by hand once it started failing.

So... anyway again, I this other other hot end, another J-head, aluminium this time, and 0.4mm, and guess what? Fed a little then jammed and almost impossible to push through by hand.

What have I tried? Lower temperature, higher temperature, lower pressure on the hobbed bolt, higher pressure, 3 different hobbed bolts, and finally a piece of paxolin board just above the heated end to shield the PEEK.

I am so out of ideas, and I'm feeling like a guy who used to have a 3D printer, which I can say isn't a great feeling.

Any suggestions will be eagerly devoured.

Anyone know what this means? (filament pulled back out of head after jam):
Here's the .5 and .3 output before it jams:
and here's the filament after it's pulled out of the hot-end, with the last cm slightly thicker:
and here's a minor fail face to face with a major fail:
Going wrong, recovering then losing it totally:
More recent with 0.4mm Alu J-Head

Looking closely at the pics of the failures, there're signs of "stiction", like the filament's sticking then releasing, giving the larger blobs. This may point to expansion into some liner tube somewhere, and its gripping the sides rather than hitting a blockage. Though why now? Humidity changes?

Update: Put a fast centrifugal fan onto the ventilated PEEK of J-Head, above the paxolin board covering the brass. Still got the same problem

Edited 9 time(s). Last edit at 03/02/2013 09:27AM by infodude.

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Mendel iteration 2
J-Head Mk4 (0.5mm & 0.4mm) 3mm sleeve
That head from eBay from Poland (0.3mm)
Wade, Wade's accessible

First thought is to verify the nozzle is heating to the temp it should be, oozing is a good indication, else stick a piece of plastic (ABS in your case) against it when hot to verify it is getting hot enough.
When you said that you replace the hot end, did you mean the entire hot end?
Here is a thought: The thermal isolator bore can get deformed and expanded internally when hot in a region after getting plugged and then subsequent usage when the liquid plastic pushes back up the bore just around the filament filling the gap (as usual). Usually at some point up the bore the melt cools enough to solidify and rides along with the filament down to the melt area. If there is an expanded region in the bore, then the plastic may cool in the expanded area and become unmovable past the lower narrower region. The heat from the melt chamber can't reach up that high efficiently and the filament won't push through.

Thanks for the excellent reply
I've since checked the nozzle temp by ramming a thermocouple into the hot end and comparing - same to 1^oC so not that.

Strangely yes, replaced the entire J-Head assembly, although they're different specs - the first had fatter inner tube with hollow bolt, the second a thin PTFE tube with no retainer.

I really like the backflow-to-wide-region idea. Another post I made shows trauma to my PTFE tube. Looks like I was printing with superhot grit at some point! I have now reamed it out and will test, but I'll be looking to replace that tube.

Thanks again,
Phil

Edited 1 time(s). Last edit at 03/03/2013 06:57AM by infodude.

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Mendel iteration 2
J-Head Mk4 (0.5mm & 0.4mm) 3mm sleeve
That head from eBay from Poland (0.3mm)
Wade, Wade's accessible

Oh! Just taken apart the nozzle (again) and found a tiny little silver ball in there! I've read about this before, little balls embedded in filament, and assumed it was a catastrophic manufacturing failure and probably a one-off. Perhaps not...

I'd heated the block with a small torch to burn off filament before cleaning, and upon touching the ball it was molten... solder then? Not from my kit, so maybe someone flicked their solder too far in the factory!

I guess if this started half-way through a reel that would explain why the stuff first appeared fine. It would also explain three nozzles failing (and could potentially cause some damage too).

Cleaned up and restarted with PLA this time, will post result.

-Phil

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Mendel iteration 2
J-Head Mk4 (0.5mm & 0.4mm) 3mm sleeve
That head from eBay from Poland (0.3mm)
Wade, Wade's accessible

oh, that is an odd one.
I never heard of that before, although many instances of bad quality filament. That would explain a lot. Please let me know if you can verify the contamination source. Include manufacturers, vendors and as many details as possible and I will put the info on the print troubleshooting pictorial guide.

Edited 1 time(s). Last edit at 03/03/2013 12:45PM by rrr7.

OK, signs so far are that it's back to its old self! Sadly when I tried to tweezer-off the ball to put it under my microscope, showing itself to be molten metal also caused its demise...

Check out RIchRap's blog entry 19 June 2012 or Google "jammed-frggn-nozzle" for previous.

Also sadly, I'd put gold and grey filament through it from 2 different suppliers before it failed, so not wanting to incriminate the other by association I'll finish off both reels and see if it reoccurs, then take it from there.

Print troubleshooting pictorial guide! Great idea. I can get good close-up pics with my cheap USB microscope, and feel free to use any already here.

Thanks for all the help,
Phil

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Mendel iteration 2
J-Head Mk4 (0.5mm & 0.4mm) 3mm sleeve
That head from eBay from Poland (0.3mm)
Wade, Wade's accessible

Thanks, I put a couple pics in.
You are welcome to add/edit content to the PTPG as you think it may help others too.

For anyone who's still reading this - I think I've got it, with a little(?) help from rrr7...
The red PTFE sleeve was pretty scored and damaged, mostly at the hot end.

The theory goes:
The melt was coming back into that part that was scored and reamed out, which would probably be fine if it carried on feeding, However, I had a 5mm retract and that would have been a problem. The cooled filament around the scored area would be gripping those score marks like a good'un, and would be wider than cold end of the sleeve, where there was no scoring, so I think that the retract was wedging the wider filament in the narrower part of the sleeve, then stripping the filament at the hobbing and wedging the filament in tightly. When the retract spun forwards again it would have less grip to push against a wedged filament.

Not sure it's right, but spinning a rough rod in the sleeve using a drill until the scores were gone certainly seems to have brought it back to life - printing PLA and ABS with no problems so far.

Thanks again rrr7

-Phil

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Mendel iteration 2
J-Head Mk4 (0.5mm & 0.4mm) 3mm sleeve
That head from eBay from Poland (0.3mm)
Wade, Wade's accessible

Glad to hear you are back up.

read also thread for same issue:
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