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.
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.
- 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
What you’ll need
Removing 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:
Detaching the PTFE tube
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.
If necessary, repeat the above steps for the other side of the tube.
Clearing the stuck filament out
- Insert the Bowden tube back in the hotend.
- 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.
- Reattach any components that you had to remove.
- 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:
- 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.
- 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.
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.
- 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.