Clearing Filament Jams on the Prusa i3 Mk3

One of the most disconcering experiences with a new printer is the inevitable jam, when filament is stuck in the extruder somewhere and you’re stuck trying to figure out how to get it out. The Prusa Mk3 is pretty well designed for maintenance, so spend a few minutes examining the problem before you start tearing anything apart.

Note

These notes are based on my experiences with the Prusa i3 Mk3 printer. If you are using a different printer, please verify the hardware details are same. These pages may be a bit rough as I revise them and add new material. Please check back regularly for updates.

The first thing to do is try to pin point where the jam is occurring.

  • Open the extruder door screws and examine inside the extruder mechanism with good lighting.
  • Examine the idler gear on the open extruder door and verify that it can rotate freely.
  • Determine if filament is snarled up inside the extruder. You may see some sticking out the left extruder port or twisted around the extruder gears. If so, you can try snipping off parts and pulling them out with needle-nose pliers.
  • A blob occasionally can form above the PTFE tubing that both prevents filament from feeding down into the tubing, and in extreme cases, even from being pulled out from the top. Trim off the blob and remove it with needle-nose pliers, and pull the rest out the top.
  • If your extruder is still jammed, you can first try poking up into the heated nozzle opening with the accupuncture needle included with your printer, but I find I either can’t find the thing, or that it snaps off easily, making the jam worse. The next simplest test is to replace the nozzle with a known-good one. Don’t toss clog nozzles! They can be cleaned up and restored to service easily.

If your extruder is still jammed, you likely have filament stuck inside the actual extruder.

  • Closely examine the PTFE tubing sticking up below the gears. The PTFE tubing itself is white. Check to see if filament is snapped off but still visible in the tube. If so, clearning it can be pretty simple. First, locate a 6 inch/15 cm length of 1.5mm rod. A hex wrench can work but may not be sufficiently long. Be sure to polish the ends to avoid tearing up the PTFE tubing. Still brass rod sold at hobby shops is ideal.

    1.5mm polished brass rod

    Fig. 56 1.5mm polished brass rod

  • With the extruder door still open, heat the nozzle up to printing temperature and insert the rod down through the top of the extruder.

    Inserting the rod through the filament guide

    Fig. 57 Rod inserted into extruder housing via top filament guide

  • Guide the rod down past the Bondtech extruder gears and into the PTFE tube. Be sure not to bend or snag the tubing.

    Rod clearance through extruder and into hotend via PTFE tube

    Fig. 58 Rod clearance past Bondtech extruder gears and into hotend via PTFE tube

  • Gently push down until you encounter resistance, then continue to press straight down gently. You are trying to push any stuck filament down into the hotend where it can be melted and pushed out of the nozzle by your pressure on the rod.

  • In some cases (for instance, if you broke off an accupuncture needle), it may be necessary to remove the nozzle to force out the blockage.

    Blockage cleared

    Fig. 59 PTFE tube blockage cleared

Note

If the filament is simply snapped off, you may prefer to remove the nozzle and poke the rod or wrench up through the heated block to push the filament up into the extruder where you can reach it with needle-nose pliers.

Jams aren’t really a big deal once you get a handle on them, but you’ll be miserable not having a tool or part to continue your print on the same night. Be sure to assemble a <Nozzle Aid Kit ahead of time.

Contact and feedback

You can find me on the Prusa support forums or Reddit where I lurk in many of the 3D printing-related subreddits.