extruder jams on larger prints and other problems

After remedying what appear to be common taz problems ( x and y axis belts coming off bearings, leaky nozzle with pla), I’m left with a few persistent issues.

These appear to be unsolvable and I can probably live with:
-after using Teflon on the nozzle threads pla pools on top of the heater block
-I’m printing pla on bare glass cleaned with rubbing alcohol and set to 60c. When I print towards the edges I get medium to poor adhesion; guessing this is due to inconsistent heat bed.

The issue I need solved:
-using the draft and high quality settings the nozzle begins to clog and ruins the print

the warning signs begin with shorter movements that have missing lines, this then extends to areas with longer movements, followed by no extrusion. I’ve tried pausing the print to clean the hobbed bolt, but it quickly becomes clogged again. Initially, tightening the screws bought me more time but I still couldn’t make it through a print much bigger than an octopus.

also, as the print progresses the nozzle sometimes brushes the previous layer and drags.

I’ve read about pla expanding over course of a print so I tried turning the bed off after the first layer without success, also I’ve read about possible z step inaccuracies, but shouldn’t this be already calibrated by lulzbot? This is my first printer and expected a steep learning curve, however I did not expect so many hardware problems at this price point.

other details: printing white pla from lulzbot at 190c, first layer at 195c, bed at 60, calibration print looks great (evenly smooshed), using draft and hq config files from lulzbot (only changed the filament dia from 2.89 to 2.87 after measuring with dig. calipers) Printing in a cool, 65f, humid room.

At this point I would like to just get through a print other than an octopus at any resolution, any tips would be greatly appreciated.

I had extruder jams very similar to yours, but with ABS. I solved this problem by removing the nozzle and leaving it in acetone for a few hours.


One thing I read after that is that a hot end does not like to stay idle at high temperature. Which is exactly what I used to do: in Pronterface I would start heating up both the heated bed and the hot end at the same time. Since on my AO-100 the hot bed takes almost 20 minutes to heat up to 110ºC, the hot end would stay idle at 230ºC for at least 15 minutes.

Now I heat up the bed, and only when it’s about 10º from reaching its targeted temperature do I start to heat up the hot end.

That might be another reason you’re having problems: the humidity. The filament absorbs moisture, especially PLA. See https://www.lulzbot.com/support/support-topics#ex_003

I do not know if it helped, but shortly after my extruder problems I purchased a dehumidifier and keep the room at less than 55%RH. I’ve since been getting very reliable prints.

Have you read this?

Budaschnozzle 2.0 PLA Solution

I had extruder jams very similar to yours, but with ABS. I solved this problem by removing the nozzle and leaving it in acetone for a few hours.

Thanks for your thorough reply Gemini, I have previously poured over your jamming problems looking for an answer, have you since tried printing a bigger print, like 3 hours plus with success?

When my printer jams I am able to raise the head and manually extrude filament (edit: after removing stripped filament), which makes me believe the head is too close to the print causing it to jam.

One thing I read after that is that a hot end does not like to stay idle at high temperature.

this isn’t a problem for me, the hot end and bed come to temp quickly and about the same time

I spend most of the year in Arizona, so I won’t be buying a dehumidifier, but I have read about removing moisture from filament by prewarming in an oven, I’ll give this a try.

Still, I would expect the result of moisture to be steam and bubbles in the print, which I don’t have, not a jammed hot end.

Without any real knowledge, my gut tells me that over the course of printing the print gets closer and closer to the hot end resulting in a jam, whether this is due to the print expanding, too much plastic being extruded, z not raising enough, or some other problem.

I’m at a loss of how to diagnose and solve this problem.

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?