Hi all,

I am fairly new to this whole Reprap thing, but I built a Prusa Mendel back in December, and I have successfully been printing since Christmas. However, recently every time I try to print, the machine works fine for about 10-15 minutes, and then the extruder jams. I have taken everything apart and cleaned it, replaced the hobbed bolt, and it still jams. Has anyone else had this problem, and what should I do?

I am using Wade's geared extruder, with a Makergear hot end and 0.5mm nozzle. Printing in 3mm PLA, with Skienforge, Pronterface, and RAMPS 1.4. My original bolt was hobbed with an M4 tap, but this time I used the Dremel cut-off tool technique to create a more aggressive bolt. This did not improve anything (The bolt just chews up the filament when it jams). Prior to this, I have printed for about 30 hours problem-free. This is starting to get frustrating . Any suggestions would be gratefully accepted.

I also attached pictures of the jammed brass tube from my hot end, after I removed the PEEK/PTFE insulator, the nozzle, and the heat core.

Thanks.

Have you recently switched to a new roll of PLA, possibly a different color from the same source or from a different source? I've found that temperature settings which are perfect for one roll aren't always appropriate for a different roll. I am guessing you are overheating this PLA, causing it to become harder to force thru the nozzle, which may have some burnt material inside it. Once you get the nozzle cleared try heating it with a torch and then shove a wire thru to clean out any obstructions. Also, check groovemount cold end, it's possible that it started melting and caused a lip between it and the barrel, which the filament will expand to fill and make it difficult to extrude past.

I have not switched the roll of PLA, but I will try playing with the temperature settings and see if that helps. The groove mount seems ok to me.

Thanks.

I had a simular issue with our first hot end. It was a PTFE brass NiChrome hot end . After constant breakdowns and rebuilds it finally worked, but only for two days. It then failed and would consistantly jam. I believe that the issue was the plastic (in my case ABS) would grow and then grip onto the brass causing the jam.

For me the fix ended up changing to a J-head design. Having a PTFE sleeve almost all the way to the melt chamber seems to have helped a lot.

Here is a link to my thread. There is a lot of good info from others in there. [forums.reprap.org]

I have finally figured it out. Thanks for all the advice. It turned out that I had a slight burr on the threaded part of the brass barrel, and so it didn't screw completely into the PEEK insulator. The plastic oozed out into the gap, cooled, and stopped the print. I cleaned up the thread and put it back together, and it's been printing great for 3 days.

EDIT: 30 minutes after I posted, it jammed again...

Edited 1 time(s). Last edit at 03/17/2012 12:00AM by peterrash.

I've been having a similar problem too.
Had a chance to solve it again in the end?

The Glass transition temperature of the plastic usually occurs where the metal heater parts meet the insulator parts (this is where there is the most significant change in temperature). If the path of the filament has a gap to expand into at this point, it will, and it will jam.

I got around this by making the hole in the insulator smaller than the hole in the nozzle/heater and press fitting them together. It doesn't allow the plastic to "catch" on anything.

I've tried to remove the final nozzle piece though, and it was moving right without jamming... so I did exclude that for my case.
Though I'm getting a new extruder piece, so I can either try the new one, or mix parts of the two to discover what's actually happening...

I still haven't figured the problem out, but in frustration I ordered a J-head hot end, as it seems that people are having success with them. Hopefully it'll be here this week, and I can get up and running again. There's nothing worse than looking at a dead printer every day...

Thanks for all the input.

I too had a similar problem, never solved it so i ordered a J-head, what is noteworthy on the J-head instructions is that it requires a cooling fan on the peek when printing with PLA, something i did not have on my previous setup (hotend v9)

That is a hot thermal barrier, put a fan on it and that should clear it right up. (Thermal barrier being the plastic part of the hot end). It causes jams because the plastic gets hot and sticky outisde the thermal barrier.

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repraplogphase.blogspot.com

spacexula Wrote:
-------------------------------------------------------
> That is a hot thermal barrier, put a fan on it and
> that should clear it right up. (Thermal barrier
> being the plastic part of the hot end). It causes
> jams because the plastic gets hot and sticky
> outisde the thermal barrier.


You could not be more wrong, did absolutely nothing putting a fan on it, not even remotely changed anything

I've been trying to print with 1.75 PLA, but am experiencing similar problems. The PLA has hardened on the inside of the PTFE insulator - effectively blocking any more filament from getting through.

I have immersed the PTFE in an acetone solution (i.e. cheap Tesco nail varnish remover ) in hopes that this will soften it. Is this a waste of time though? (I know it can take approximately a day for the acetone to have any effect - would prefer to know sooner rather than later if I'm wasting my time.)

I also tried re-drilling the hole in the PTFE barrel to solve the problem. This was somewhat successful, but pretty messy (the PLA tends to wrap itself around the drill-bit for example - and is proving tricky to remove). I also tried to re-melt the PLA within the PTFE using a hot-air gun, but the process is quite awkward.

In case it's relevant a picture of my hot-end can be seen here (first attempt - I acknowledge it could do with enormous improvement).

Edited 1 time(s). Last edit at 04/10/2012 11:30AM by dslc.

Having read how you made the hot-end, I suspect that part of your problem might be poor tolerances. My understanding is that if the hole is too big, or if there is any gap between PTFE and brass internally, the plastic can flow up and solidify in the PTFE. Alternately, if the hole is too small you can also get jamming, as the PLA expands when heated.

Gonna share my experiences, they might help somebody down the line.

I started with a mendel-parts v9 design hotend, not supplied from him, but via makemendel.com

i tried every trick in the book, even made new brass peices on a lathe. i tried both 2.2mm diameter rods, and 4mm rods.

I was trying to print with 1.7 pla from pla3d in sweden. When manually feeding pla i could extrude for about 5-10 seconds before it would jam, when extracting the filament i noticed it was expanding in size and jamming against the inner wall in the rods. So i asked around on the IRC channel and they said it was a thermal issue, so i added a fan and pointed it at the peek blocks on the outside. result = nothing changed.

Took another peice of advice, bougth a J-Head from hotends.com waited a week for it, mounted it and left the fan on pointed at the peek block on the new J-head, that fixed all my jamming problems

The plastic will always expand to the size of the tube when it gets past the glass transition temperature. To get the least resistance the bore should be only a little bigger than the plastic (so the un-melted diameter will pass through it) and it has to be something very slippery, e.g. PTFE or have an increasing taper like a mould draft.

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[www.hydraraptor.blogspot.com]

load of theoretical bull, my filament was jamming and a new extruder = fixed

Asger, nophead explained why it is happening, not just for your benefit, but for the benefit of all users of the forum. He knows more about the theory and application of 3d printing than most people on here, it certainly isnt thoretical bull. I'm glad you have fixed the problem for yourself, but I'm also glad Nophead explained why it happens as I'm trying to learn why I'm having problems with my hot end.