Filament Jamming

As the subject suggests I am looking for ideas on how to prevent Filament Jam.

Sometimes It’ll Jam 2 hours into a perfectly good print, Other times it’ll jam within the first 30 minutes of printing. It seems to only jam when printing with PET + or ABS Filament. If i hand press the Filament into the extruder it flows freely without any curling near the opening of the extruder. I’ve tried some variants of printing faster / slower to include higher temperatures but neither seem to help prevent the Filament from pig tailing in the extruder assembly. Any help is as always appreciated.

Also Since it jams with ABS which shouldn’t swell like PLA when it is heated could the issue be more mechanically related?

I have printed with abs on the same spool before with zero issues. It seems the jamming is coming from something recent that has happened. Could the extruder hobbed bolt be over tightened causing the Filament chewing / Jamming? How tight is tight enough? Both Herringbone gears appear to be smoothly rotating during prints.

Edit
Could it also be possible that my hot end is not heating up properly as it used to?

Hey Chrono,

For what its worth, I just had a heck of a time with jamming filament. Turns out that the stuff I was using had some poor quality control, as its diameter had changed about halfway through the spool. it was some cheaper ABS on amazon. It was too large to be fed through the PTFE tube leading into the hot end. I could manually push it through, but the hobbled bolt just chewed through the filament instead of pushing it.

Might double check the diameter of the filament and see if it looks consistent, as you can probably measure the end of it as well if it is poking through the spool.

Good Luck!

-TJ

Things that can cause jamming related scours:

  1. Your nozzle is too close to the bed. If the molten ABS can’t flow at the rate it expects to flow, it builds up in the nozzle. A lot of people feel this is related to a clog, but its usually just backpressure. At any rate, once the pressure buildup happens, you are basically trying to put more filliament into an occupied space and the filliament strips out. It’s basically the same effect as trying to extrude plastic into a solid brick wall.

  2. Your parts are lifting and causing the nozzle to end up too close to the bed for enough of the print to cause backpressure.

  3. Your idler arm is too loose. From the pictures I can’t really tell. the middle straight blue filliament looks like it has a good tooth pattern from the extruder, possibly a little shallow but i’d need to see the extruder to tell.

  4. Your idler arms are too tight. In this case the printer will almost always instantly jam.

  5. The Thermistor or heating element are partially failing. This can happen, buy an inexpensive infrared point and measure thermometer ($35 - $70) from your local tool or auto repair store and use that to verify the hot end temperature. If you are within a few degrees of where you should be, everything is probably ok. If there is a major difference you might have failing, but not yet failed components.

  6. The filliament diameter changed mid spool. This one is actually fairly common. Check the filliament diameter with calipers and adjust your SLic3r software accordingly. Usually the stripped filliament issue will be caused by filliament larger in diameter than your slic3r thinks it is, which leads to overextrusion and back pressure.

  7. There is an actual jam in the hot end. This almost never happens. I’ve seen one person have a chunk of their PTFE tube break off, and one person who had debris in the filliament itself. Every other instance of this I have ever seen or heard of has been backpressure or nozzle position related.

Thank you Piercet and TJ for the detailed responses.

I went ahead and bought an Infrared temperature gun (rated for up to 320C) and the hot end is indicating that it is anywhere from 200-210 degrees C on the gun when the temperature is set to 230 C on the Taz 4.1. When the machine is cool the hot end matches the ambient temperature.

While i understand that shiny objects may not indicate an accurate temperature from an infrared non contact source, shouldn’t the variation be less than the order of 20-30 degrees C? Is it safe to assume that the temperature of my hot end is incorrect and the parts require replacement?

As far as the other potential problems:

With regards to nozzle height I usually try to ensure the nozzle is far enough away from the bed to prevent the filament from not sticking. This usually results in a few passes of a bad skirt and re-attempts before the print is commenced. The bed is usually checked for level 1-2 times a day and certainly any time a part remains stuck to the bed that requires a little prying.

Initially I have seen some parts lifting from the bed until I switched to Kapton Tape. With Kapton tape and 3-6mm of brim parts no longer depart from the bed surface. While increasingly difficult to remove the trade off was always considered a success in comparison to restarting due to a failed print.

When the filament started to jam I first checked the idler tension. Adjusting it from 10 cm as recommended to tighter and looser by about 5mm in 1mm increments with no success.

The filament appears to be a high quality and is measured periodically throughout the spool for dimensional accuracy. I’ve used both calipers and fixed measuring blocks to verify its diameter to within 2 decimal places. When i was feeling particularly nerdy I even went as far as to measure it with my cnc machine to verify the measurements of the the measuring tools…

As far as an actual jam in the hot end I would assume that this could be what causes some machines filament to curl when hand pressed through the nozzle. Mine comes out in a straight line with no curling when hand pressed. Outside of that i’ve little idea how to verify a potential jam without the worlds smallest borescope or an additional nozzle (which i’ll probably get anyway at some point in time…

Could be variance in the thermometer, but mine generally measures much closer to the expected temperature than that, within 5 or so degrees +/-. I’d start looking at the thermistor or heater core. There are threads here that mention which specific resistance they should show on a multimeter. Find those (I think Orias posted them?) and then test thhose two components. if they do show a difference from expected, order new ones or get warranty service. If either of those are failed, the replacement part should be very inexpensive.

At least for me, I was able to solve my filament jamming problem by cooling the aluminum mount plate (by making a bigger one with a fan on it). See: https://forum.lulzbot.com/t/heat-creep-filament-jam-on-long-prints-a-solution/854/1

Viktors,

Thanks for the tip. Were you printing with ABS or PLA when your filament was jamming? Those jams do look identical to some of the jams I was having prior to my Taz meltdown. I should be able to CNC the parts i need in a similar manner. Once i’ve got everything up and running again i’d be curious to give it a try. Does that massive fan interfere with the X axis movement at all from the added weight on a diving board?

I was thinking of just adding larger cooling fins to the Nozzle vice the small ones they already have on there. Since i primarily print with ABS i try to avoid the cooling fan when possible. Larger fins should mitigate a good portion of the heat from rising up but i’ve a feeling it may come down to trial and error. I’ll probably end up making my own nozzles not long from now as well just for fun but we’ll see.