extruder jams on larger prints and other problems

yes, i read this and used solution 3, guess i should have used 1, hopefully the pooled pla isn’t negatively affecting the print

I wonder if a fan with shroud pointed to the upper section of the hot end might help?

I’ve read that for most other hot ends, a fan is necessary with PLA so it doesn’t get clogged.

See http://www.thingiverse.com/thing:26291

I think you’re exactly right Gemini!

looks like the Buda 1.2 had the same PLA jamming problems due to “heat creep” and a fan pointed at the top half of the extruder solved it:

I dug through my trash collecting all my filament jams for further inspection, managed to find 6 of them. They all exhibited filament swelling well above the hot end where the filament would finally mushroom into a jam.

from top to bottom:
pre-jam filament measured 2.86-2.89
jam measured 3.18-3.47
swelled filament measured 3.00-3.20

There also appears to be a correlation between deeper teeth marks (higher tension on hobbed bolt) and thicker jams. I’m guessing that more bite on the filament was able to force thicker swollen filament through the hot end, buying more time. Of course, this also further heats up the extruder motor leading to the inevitable jam.

another thought; the jams are beginning in smaller areas with shorter movements because the high number of retractions are drawing heat and softer filament higher into the extruder where the jams occur. Also, the filament stays in the same place longer picking up heat. This is opposed to large perimeters, where a steady flow of cooler filament is drawn through the extruder, so my theory goes.

We do recommend that users printing with PLA mount a fan on the carriage. More information can be found here: https://www.lulzbot.com/support/3d-printing-pla-plastic-filament. This mount will work for the stock batch 1 TAZ 3D printers. Printing with a fan has improved my PLA prints.

the support article mentions a fan to cool the print, but will this help with jams related to heat creep on lengthier prints?

I plan on cooling my print AND the top half of the extruder assembly, is this not recommended in your experience?


I’m wondering the same thing, I’ve been reading up on the RepRap forum, and it seems that with PLA having two fans (one pointed toward the upper part of the hot end, the other toward the print) would be the way to go. Otherwise you’d need to cut down on printing speed if you don’t cool the print.

You know, considering how I’ve have very few problems printing with ABS, and the problems I keep reading on the forums about PLA, I don’t see any reason to want to print with PLA. But I admit I haven’t printed anything very large yet. In any case my AO-100’s print bed is only 200x190mm.

Yes, I’m beginning to think the taz has an abs bias; the nozzle leaking pla and jamming being red flags.

so, the attached pictures show that the pla jams are occurring immediately above the heat sink. I take this to mean that over the course of a longer print the sink can’t keep up with accumulated heat generated by the hot end and extruder motor.

One fan will be aimed at this juncture while trying to minimize air flow over the hot end.

If too much heat staying in the nozzle and creeping up the heatsink is really the cause, there is another way to get that heat out…

Print Faster.

the faster you can feed that nozzle the cold filament, to soak up that excess heat, the less it can travel up.
What speeds and layer thickness (and even width) are you printing at? all will affect how fast the filament is fed into the hot-end.

That’s a great idea! No problems with printing faster.

Though, at the current settings, standard draft config. provided by lulzbot, the machine can shake pretty violently during shorter movements. I would like to deploy the mods you made to improve rigidity and accuracy before going faster, but any suggestions you have would be welcome. I have started using the custom g-code you developed to limit travel speed.

Also, printing faster means that heat is getting dumped into the print, which has its own problems related to expansion on a larger print. Hopefully a fan on the print will remedy this and I can look at printing faster with pla.

agreed, I’m at a loss; I printed the fan mount and it is not clear to me where to install and orient the fan, any tips, especially a photo of it in use would be great

Just wanted to bring resolution to this topic:

-filament jamming on 2+ hour prints was solved by mounting a fan directed at the heat sink. Prints of 7 and 18 hours have been completed without jamming. While a second fan was mounted and aimed at prints, this was kept off during my tests.

the heat sink fan is plugged into the extruder #2 fan slot and kept on for the entire print with the following gcode entered into the slicer gcode prefix:
M42 P6 S255

-the pla pooling on the heater block was solved by Teflon being applied to the threads ABOVE the heater block where the all thread connects to the heat sink. After twice using the lulzbot fixes and still experiencing pooling, taking apart the hot end revealed the source of the leak.

both of these problems and fixes point to the Buda 2.0 hotend having serious flaws with regard to heat creep and printing pla

I’m glad to hear that PTFE tape on the threaded extension solved the PLA leaks from the PEEK insulator. We have not encountered leaks from the PEEK insulator before, in all our testing. We used PTFE tape similarly yesterday when we were testing the hot end for PEEK leakage.

Scott, do you have the STL of that dual fan mount you’re rocking?

See https://forum.lulzbot.com/t/taz-fan-mount/197/9

Some users have encountered flaking or delamination when removing parts when printing on bare glass. We recommend printing with either the stock PET surface, or with the new PEI print surface that some of our more advanced users are using with great success.


I’ve been having a similar issue with ABS. After about 2 hours into a print the extruder jams. I’ve been reading a lot regarding ideas to correct. My dabbling with this problem seems to support the “heat creep” idea of the material getting exposed to heat prior to entering the heat chamber. As the knurled bolt pushes more material it bunches up the soft plastic and eventually causes a block. As others, I’ve experimented with providing extra cooling to the heatsink on my extruder. My issue has been how to push ventilation air through the heatsink. I’ve looked at the ideas of placing fans and directing the flow of air through the fins. This I find is too much work (havimg to design a holder for the fan) - not to mention the extra weight on the hot end assembly.

Here’s my last try. Instead of the complication of hanging a fan near the heatsinks, I’ve chosen to direct air through a silicone hose (about 5mm ID). This hose is nothing more than silicone aquarium air hose. I drive air through a cheap aquarium pump. See attached pics on how the hose attaches to the hot end. The air pump is rated at about 5L of air per minute. Seems to be enough to cool heatsink without affrecting the actual print. I’ve chosen to direct the air to the lower part of the heatsink. Total cost less than $20. Total install time -less than 10 minutes…

So far, results have been promising… no jams… I’ll keep my fingers crossed.

You Sir are a true lifesaver :slight_smile:

I’ve been using this cooling approach since last October. I can report ZERO issues with clogs since then. TAZ is at point of high reliability. I just set up and go. Good luck with yours!

im having same problem tonight for the first time after using large quantities of acetone in the room. my method for using acetone is evaporating it on abs so i tought it might ve effected unprotected abs spools (i do my process in closed glass bowl but not entirely airtight) i can easily hold heatsink barehanded while printer is on but ill also try tunneling more airflow to heatsink.