When 3D printing, it is likely to at some point end up with stuck filament in a PTFE tube. Whether it is broken filament in a Bowden tube or a clogged piece of filament stuck in the PTFE tube of the hotend, it must be dealt with before you can continue printing.

Luckily, solving this problem is not very hard. Manually cleaning out the tubing is usually enough to make the 3D printer operational again. But it is important to know the best way of doing this.

In this article I will show you how to remove stuck filament from PTFE tubing, explain the cause of the problem and what you can do to prevent it from happening again.

What causes filament to get stuck in the PTFE tube?

The main cause of filament breaking and getting stuck in Bowden tubes is brittle filament. Some filaments, like PLA, tend to become brittle after they absorb too much moisture from the surrounding air.

Leaving filament out for a long time without using it gives it ample opportunity to absorb moisture. The next time you print with it, it might be brittle and can easily break. This is why it is important to store your filament properly and keep it dry.

As for filament getting stuck in the short PTFE tube of a hotend, that can also have other causes, such as heat creep or a gap between the tube and the metal parts of the hotend.

An E3D V6 hotend heatsink with PTFE tube sticking out of the top.

I might write a more detailed article on clogged hotends, but for now I will just focus on how you can get the stuck filament out of the PTFE tube.

What can you do to prevent it?

There are a couple of things you can do to prevent filament from breaking and getting stuck:

  • The most important thing is to make sure that your filament stays dry and does not absorb a lot of moisture from the air. So, when you won’t be using it for a while, store it in a box or in sealed bags with indicating silica gel beads. This is especially important for PLA and nylon filaments which absorb a lot of moisture.
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Recommended reading: DIY Filament Dry Boxes →
  • Use high quality filament. Low quality filament is more likely to have an inconsistent filament diameter. If a section of filament is too wide for the tube, it has the potential to get stuck.
  • Another thing you can do is limit the friction and tension on the filament. The easier the filament can get from the spool to the hotend, the less likely it is to break anywhere along its journey. You can do this by:
    • Using a high quality PTFE tube. Capricorn Bowden tubing is an excellent choice, mainly due to its tight tolerances and high temperature resistance.
    • Optimizing the path of the tube. Bends with a small/tight radius create a lot more friction than bends with a large/wide radius. So wherever possible, make sure that the path of the tube is not too constrained.
    • Making sure that the internal diameter of the PTFE tube is the right size for the filament that you are using. If it is too narrow, the filament can’t get through at all. If it is too wide, the filament can ‘buckle’ and create extra binding and friction.
    • Making sure that the filament spool is able to roll freely.

How to remove stuck filament from a PTFE tube – Step-by-step

Tools & Materials

  • Whatever you need to disassemble your extruder and get access to the PTFE tube coupling. Typically a set of hex drivers will do.

For filament that is stuck outside of the hotend

If you have snapped off filament stuck in a Bowden tube or other piece of long PTFE tube, the easiest way to fix it is to remove the tube and clear it out:

Removing the PTFE tube

  1. If necessary, open up the extruder carriage to get access to the coupling that holds the PTFE tube. The steps for this will vary depending on the specific 3D printer you have. If you don’t know how to do this, checking the manual/documentation for the printer will help.
  2. Remove the collet clip from the Bowden coupling. This is a typically blue, red or black clip that looks a bit like a horseshoe.
    A hand removing a blue collet clip from a 3D printer hotend coupling.
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If you are not using these, you should! They prevent the PTFE tubing from moving back and forth when extruding and retracting. This gives more precise extrusion and also prevents clogs. You can easily 3D print these clips yourself. Here are some 3D models that you can use.
  1. Push the collet down as far as possible. This disengages the coupling’s metal teeth that hook into the tube.
    A finger pressing on an embedded bowden coupling
Close-up of the metal teeth inside of a PTC coupling used for PTFE tube.
A close-up of the teeth that grab onto the tube.
  1. Pull the Bowden tube out while still holding the collet down. It can help to lightly push the tube down first. This assists in getting the metal teeth out. Sometimes they get a bit stuck.
    A hand pulling PTFE tube out an embedded bowden coupling.
  2. Do the above steps again, but this time at the other end of the tube.

Clearing the stuck filament out

  1. Place one end of the tube in a PTC coupling and place it in a vice. Alternatively, you can have someone else hold the other end. What matters is that the tube is held straight, as this makes removing the stuck filament easier.
    Teflon tubing in a PTC coupling, clamped in a vise.
  2. Stick something long and thin down the tube and push the broken filament out. An easy way to do this is by using a piece of fresh (non-brittle) filament. Alternatively, you can use a long metal rod like a thin welding rod, or my favorite, a guitar string. Be careful not to use anything sharp that can scratch the inside of the tube.
    A guitar string being used to remove stuck filament from a PTFE tube.

Reassembly

  1. Insert the Bowden tube back in the hotend.
  2. Clip the collet clip back on. Make sure to push the PTFE tube all the way down first. Then pull up the coupling ring and add the collet clip.
  3. Reattach any components that you had to remove.
  4. Repeat the previous steps to reattach the other end of the tube.

For filament that is stuck inside of the hotend

One of the most common causes of filament getting stuck in a hotend is a PTFE tube that does not reach all the way to the heatbreak or nozzle. This creates a gap that filament can melt and expand into. When this happens, the molten filament can cool down into a blob that prevents the filament from moving further.

One way of preventing this is to use collet clips mentioned above. These prevent the PTFE tube from sliding up when retracting and prevent the gap from forming.

Filament that is stuck in the PTFE tube inside of a hotend can be harder to remove. Fixing this (without damage) often involves opening the hotend up to remove the clog. It is sometimes possible to pull the PTFE tube out through the top, but this can lead to damaging the tube because it takes a lot of force.

The exact procedure for this depends on the exact hotend that you are using, but it will be roughly like this:

  1. Partially unscrew the nozzle. This loosens the heatbreak at the other end of the heater block.
    A spanner wrench being used to unscrew the nozzle from a hotend heater block.
  2. Unscrew the heater block from the heatbreak.
    A hotend heater block unscrewed from an E3D V6 heatbreak.
  3. Remove the heatbreak from the heatsink. If it is too stuck to unscrew by hand, you can thread two thin M6 nuts on the end and tighten them against eachother. After that, you can use a spanner wrench on the inner nut to unscrew the heatbreak.
    A heatbreak unscrewed from a E3D V6 heatsink.
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Be careful when unscrewing the heatbreak. The thin, non-threaded part is fragile.
  1. Push down the ring on the coupling and push the PTFE downwards. Now that the heatbreak is gone, the tube can come out through the bottom along with the stuck filament.
    A hand pushing a PTFE tube with stuck filament through the heatsink of a disassembled hotend.
  2. Pull the tube out through the other end. You might need to push it through with some kind of tool from the top end.
    Teflon tubing with stuck filament being pulled through the bottom of an extruder hotend heatsink.
  3. Remove the filament from the PTFE tube. Typically it can be simply pushed out with something like an allen key. If it is really stuck, see the method below.
  4. Reassemble the hotend. Make sure that the tube is flush against the heatbreak (or nozzle, depending on the hotend design) so that no melted filament can escape to unwanted places.

If the PTFE tube is damaged in any way, it is best to replace it. A damaged tube is likely to cause issues in the future.

What if you can’t push the filament out?

Sometimes, the filament can get really stuck in the PTFE tube and can not be removed by hand. In that case, boiling the tube in water can help. This softens the filament inside and afterwards you can push it out. The PTFE does not get harmed by the boiling water, as it is resistant to much higher temperatures.

This method is safer than using a heat gun or any open flame to soften the filament.

Conclusion

Stuck filament in a PTFE Bowden tube or hotend is inconvenient, but not the end of the world. With a bit of careful disassembly and cleaning, you can have your extruder back up and running in no-time.

You learned:

  • Why filament gets brittle and breaks.
  • How to prevent filament from getting stuck in PTFE tubing.
  • How to fix stuck filament in your Bowden tube or hotend.
If you find this article useful, please share it or leave a comment. I love to hear your feedback and questions!

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