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Distasteful at Best

Filament Jam – 3 Easy Fixes

Picture of Reef Morse
by Reef Morse
Feb 19, 2019
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Frustrated by filament jams in your hot end? Need help fixing them or keeping them at bay in the future? Stop filament jams from ruining your day (and your printer!) by following these simple tips.

Filament Jam Fixes Time and Money

Filament jams can lead to missing layers or even the entire top of a print!
Filament jams can lead to missing layers or even the entire top of a print! Source: vio.net.au

We’ve all had the unpleasant experience of waiting for a print to finish only to return to missing layers, a bundle of spaghetti, blobs, or uneven filament deposition. These issues can arise from several sources, but here, we’ll focus on filament jams

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Filament Jam Fixes What Is a Filament Jam?

This filament has been ground down by the extruder gear.
This filament has been ground down by the extruder gear. Source: Benjamin_Krygsh / 3D Hubs

Filament jams happen when the extruder can’t push filament through the hot end. The extruder either grinds the filament until it’s so thin that the gear that advances the filament is no longer in contact with it or the motor that drives the extruder stalls because it’s overloaded.

No matter what kind of extrusion system you use — direct drive or Bowden — you’ll eventually encounter this problem.

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Filament Jam Fixes Three Problems and Their Solutions

Filament jams can lead to spaghetti instead of a print.
Filament jams can lead to spaghetti instead of a print. Source: 3dprintboard.com

In the following, we’ll look at three common problems that lead to filament jams. The first occurs when stuff that isn’t filament gets into your hot end and clogs the nozzle. The second happens when the hot end is pushed against the bed and filament can’t be pushed out of the nozzle. The third is a loss of temperature control in the hot end, resulting in filament too cold to pass through the nozzle.

For each problem, we’ll offer some short and long term solutions. We’ll also provide some advice on what not to do when you’re desperate.

Ready to print jam-free? Let’s go!

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Filament Jam Fixes Problem #1: Clogged Nozzle

Gunk removed from a hot end using semi-cooled filament.
Gunk removed from a hot end using semi-cooled filament. Source: antonmansson.com

Cause: This can happen at any time if dirt or grit gets into the hot end and plugs the hole in the nozzle. The offending substance can come from two sources, the filament itself or from dust or dirt that adheres to the filament.

Reason: Some cheap filament is made under circumstances that allow dirt to fall into the vats where the plastic is made. This dirt winds up in the feedstock from which the filament is made. Dirt can also get into the filament during the extrusion process that melts the feedstock and pushes it through a nozzle to make the 1.75-mm or 2.85-mm filament. If the plastic was recycled, bits of contamination can enter the feedstock.

Even if the filament is squeaky clean, as soon as you open the packaging, you expose the plastic to the dust and dirt from the environment around your printer.  

Solutions:

  • Short-term: The first thing you have to do is get that pesky material out of your hot end. One way is to use a piece of wire that’s smaller than the diameter of your hot-end nozzle. Disengage your extruder so that you can push the plastic into the hot end by hand. This is quite simple for Bowden systems — just remove the Bowden tube from the hot end. (You may have to heat up the hot end first.) Next, make sure the hot end is at the extrusion temperature of your plastic and then push down on the plastic while pushing the wire into the nozzle. This will often dislodge the blockage. If the blockage is small, it’ll then pass through the nozzle. If this doesn’t work, heat up the hot end, let it sit at temperature for a minute, and then turn it off. As the hot end cools, the plastic will begin to harden. At some temperature, it will be difficult to pull the filament out of the hot end, but it will come out completely. This is around 90°C for PLA. If done correctly, the plastic will come out in the shape of the inside of the hot end and you can often find the foreign substance embedded in the plastic.
  • Long-term: Change your filament supplier to someone that has better quality control. Most name-brand suppliers are excellent sources of high quality, clean plastic. To solve the local dust problem, wrap a clean, lint-free cloth around the filament just before it enters your extruder. This will remove any dust that sticks to the filament (but make sure the cloth is lint-free or else you will just add to the problem). There are several filament cleaners available for free from local print repositories.
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Filament Jam Fixes Problem #2: Plastic Isn't Flowing

The first layer with the nozzle at varying heights.
The first layer with the nozzle at varying heights. Source: Prusa Printers

Cause: Either liquid plastic has hardened in the cold side of the hot end or the nozzle is too close to the bed.

Reason: If the hot end has been sitting at a high temperature for a period of time, the plastic can become very fluid. When a new print is started, the material will be pushed into the cold side of the hot end, solidify, and cause a clog. If the hot end is too close to the bed, so that the tip of the nozzle rubs against the surface of the bed, this will also prevent extrusion of plastic. In both cases, the filament next to the idler wheel will be ground down by the gear that pushes the filament into the hot end. Thus, the filament is no longer pushed into the hot end.

Solutions:

  • Short-term: The same trick for removing debris from the nozzle will also work to clear a hot end that’s plugged with solidified plastic. Again, use the wire if you need to help get plastic flowing. If your nozzle is too close to the bed, you may need to relevel it or adjust the nozzle’s Z offset.
  • Long-term: At the end of each print, while the hot end is still hot, push 20–30 mm of filament into the hot end to clear out the fluid plastic and then retract the filament until it is completely out of the hot end. This will prevent the filament from melting any further and causing a clog. The initial push is important; if you forget it, you’re leaving fluid plastic behind, which will make the problem reappear. Careful leveling of the bed using a multi-point leveling procedure will usually help with problems of the hot end hitting the bed.
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Filament Jam Fixes Problem #3: Missing or Rough Layers

Bad and burnt wiring can lead to heater problems and filament jams.
Bad and burnt wiring can lead to heater problems and filament jams. Source: Reef Morse / All3DP

Cause: Bad temperature control of the hot end.

Reason: There are two major reasons why the temperature of the hot end can vary: physical (airflow) and electrical (thermistor failure, weak or broken wiring to the thermistor, or broken or burnt wiring). These can be vexing problems because they can be intermittent.

Solutions:

  • Short-term: Sometimes you can use an extra thermistor stuffed into a crevice of the heater block of your hot end. Unplug the old thermistor, plug in the new one, and see if the situation improves by monitoring the temperature of the hot end with your printing software. If this fixes the problem, replace the old thermistor. If not, you’ve narrowed the problem down to hot end wiring.
  • Long-term: If you’re lucky, the thermistor or wiring will fail either open (the thermocouple is not connected) or closed (a short circuit). A voltmeter set on a low resistance scale (1000 Ohms or so) will show either infinite resistance (open) or 0 resistance (short).  In either case, replace the thermistor and its associated wiring. If the problem is intermittent, you can sometimes get an idea of what’s happening by watching the power LED on the circuit that supplies the power to the hot end. At temperature, this LED will turn on and off at a predictable rate when everything is working correctly. If it goes on or off intermittently for a long period, you should look carefully at the wiring. If you jiggle it and the hot end suddenly goes on or off, you have a wiring problem and should replace the affected wires. 
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Filament Jam Fixes What Not to Do

Your hot end is not a Crème brûlée. Don't do this!
Your hot end is not a Crème brûlée. Don't do this! Source: modernistcuisine.com

The methods described above for solving extrusion problems are simple and are intended to be useful for a majority of situations. We do not recommend any action not approved by the makers of your printer or hot end.

Looking online, it’s easy to find drastic methods for cleaning out hot ends. These are last-ditch efforts that can end badly. If in doubt, contact the manufacturer.

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Filament Jam Fixes Final Thoughts

And away we go...
And away we go... Source: blog.sciencemuseum.org

Filament jams are annoying, but they can be solved with a little time, effort, and a few tools. Having these tools and tricks available will help you to print successfully even in the worst of times!

License: The text of "Filament Jam – 3 Easy Fixes" by All3DP is licensed under a Creative Commons Attribution 4.0 International License.

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