Filament ground or chewed by the extruder

Symptom

The filament has a notch or flattened section and there is plastic dust or shavings in the extruder gears. The extruder stops pushing even though the motor turns, often with clicking or squeaking.

Likely causes, from most to least likely

1. There is resistance further down (clogged nozzle or heat creep): the gear can't advance and eats into the filament.
2. Idler tension too high (the teeth bite too hard) or too low (the filament slips and wears).
3. Dirty gears packed with plastic, which grip poorly.
4. Low temperature or high speed for that material, forcing the extruder to push harder than it can.
5. Gears misaligned with the filament path, or a blocked PTFE tube.

Checks to tell which one it is

• Unload the filament and look at the section that was in the extruder: a deep or flat notch means it has been grinding.
• With good light, look at the gear teeth: if they are packed with plastic, they need cleaning.
• With the nozzle hot, push by hand: if it is very hard, the cause is in the hotend.
• Check the tension screw position against the manufacturer's guide.

Before you start

Before taking anything apart, cleaning or adjusting it, switch the printer off and unplug it, unless a step says otherwise, and do not touch the nozzle, the heater block or the bed until they have cooled down. If in any doubt about electricity, heat or moving parts, stop and ask a professional.

Step-by-step fix

1. Remove the damaged section

   Unload the filament with the nozzle hot, cut off the chewed section and load it again.

   Check: The fresh filament feeds through the nozzle without jamming.

   If that does not fix it: Clean the gears.

2. Clean the gears

   With the printer switched off and unplugged, remove plastic from the teeth with a toothpick, a brass brush or compressed air and check that they turn freely.

   Check: The teeth are clean.

   If that does not fix it: Adjust tension and alignment.

3. Adjust tension and alignment

   Set the idler screw as the manufacturer says, neither too loose nor too tight, and check that the gears line up with the filament inlet and the outlet tube.

   Check: The filament feeds without deep marks.

   If that does not fix it: Remove the resistance in the hotend.

4. Remove the resistance in the hotend

   If pushing by hand is hard, unclog the nozzle (push fresh filament by hand, thin needle or cold pull) and make sure the PTFE tube isn't blocked.

   Check: The filament goes through with little force.

   If that does not fix it: Adjust temperature and speed.

5. Adjust temperature and speed

   Use the temperature from the material profile; if needed, Prusa suggests raising it by 5-15 °C. Lower the speed if the problem appears on fast sections.

   Check: The extruder stops grinding the filament.

   If that does not fix it: If it keeps happening, contact the manufacturer's technical support.

Prevention

• Clean the extruder gears regularly.
• Don't overtighten the extruder idler.
• Don't print faster than the hotend can melt.

Still not fixed?

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Printers it applies to

Any FDM (filament) 3D printer, from any brand.

Official sources

This guide summarises the official documentation linked here:

• Extruder noises · Prusa Research
• Clogged nozzle (CORE One, CORE One L, XL, MK4/S, MK3.9/S) · Prusa Research
• Under-extrusion · Prusa Research
• Max volumetric speed · Prusa Research