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Trouble setting extruder tension - plastic dust gets into tube

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No matter how I adjust the tension spring/bolt in my Ultimaker extruder, the filament is getting ground up, and plastic dust is getting drawn up into the bowden tube, resulting in an eventual jam.

I've backed off the bolt so that the distance between the blue plastic block and the washer at the other side of the spring is 12.39mm and it's still happening.

When initially feeding the filament (before it gets to the hot end, so no resistance) I can see very small dimples in the filament caused by the knurled bolt.

What should I try next?


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The extruder mechanism should be able to push the filament just fine, without grinding it, so long as a) there isn't any physical impediment to its path, and b) you're printing at a sufficiently slow volume per second, so that necessary force isn't too high. Once it gets too high, then the filament stops moving, and the teeth grind it, rather than pushing it.

So... firstly check for any restrictions. Is the Bowden tube squeezed or damaged at either end, or has the teflon coupler at the hot end gotten melted or damaged so that it presses on the filament?

Then... consider what speed you're printing at. For best results, make sure that speed x layer height x bead width is less than 8mm³/s on an UM1.

Also, don't use the Ulticontroller to advance or load filament - it can push it waay too fast. Just turn the big gear by hand.

Finally, check your retraction speed settings... you probably don't want to be retracting much above 35mm/s - especially if you have the firmware from Cura 13.12, or another custom-built firmware that fixes the retraction speed bug. Retracting too fast, or doing lots of retractions close together can grind the filament - especially on a UM1.


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I doubt it's retraction as I believe the speed is capped at 25mm/sec typically - but I haven't looked at Daid's latest build.

I bet you are simply printing too cold or too fast. What is your temp, layer height, and print speed?

For example 190, .2, 100mm/sec will grind up your filament. But 220, .1, 100mm/sec should be fine.

My spring compression amount by the way is 11.5mm and Illuminarti's is 11.0mm. That's with the filament loaded and the clamp closed.


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