A knotted filament is annoying because it may cause a nicely running print job to fail in seconds. Here you'll find everything you need to know to solve and prevent this issue.
It happens again and again — a print fails because the filament becomes tangled and can therefore no longer be transported by the feeder. Without a filament sensor to pause the printing operation, a printer will simply continue to extrude, even if no material comes out! What’s left is a ruined object, sitting semi-finished on the print bed.
In this article, we explain why tangling happens, how to fix it, and how to prevent it in the future.
Many beginners think that, when a print fails from tangled filament, the spool has already been wrongly and not carefully wound by the manufacturer. In fact, this isn’t possible because spools are wound by machines.
If one end is attached to the spool and the other comes out of the extruder, a winding error is in fact impossible. Spools are therefore always delivered correctly, without knots. (That is, unless they’re coming from dubious sources.)
So if it’s not the manufacturer’s fault, what’s the problem?
On a new spool, the filament end is either pulled through a hole or fixed in place with tape. If the filament end is loosened and released, the spool will inevitably unwind a little. With a little bad luck, the end can push itself under another winding and already you have a knot in the spool.
Often one doesn’t immediately recognize this knot, which only becomes noticeable at a later time, like when the nozzle is extruding phantom material.
Normally tangling happens during loading or unloading because the end is being allowed to move freely. Yet, even if you do pay attention, it can also happen that the filament becomes “tangled” during printing. Especially stiff filament may jump off the spool and wrap itself around the filament holder. There may not be a knot, but the result is the same: Unable to rotate, the spool stops providing material to the hot end.
No matter how stubbornly filament is tangled, one can always undo a knot without unwinding the whole spool. In fact, unwinding typically worsens the problem as the knot simply becomes more and more tightened through pulling the filament off the spool.
To get the knot out of the spool, you need to lift a few turns, including the knot, from the spool. If you lift too few turns and you can see three paths coming from the spool, then you haven’t caught the knot. More windings have to be removed until only a single path leaves the spool. Afterward, simply rewind the filament under tension again and undo the knot when you reach it.
An alternative method is to step-by-step unwind the filament while maintaining pressure on the point where the strand leaves the other spool. In other words, one hand will be both holding the spool and pressing — with one finger — the loose strand against the underlying coils. Everything “behind” this finger should be tight. Then, with the other hand, take hold of the loose strand, maintaining tension, and slide the pressing finger back along the strand. Continue doing this until the knot is directly behind your finger. Then, instead of sliding the finger back (this would only push the knot back), grab the strand from behind the knot, and pull the loose strand all the way through! Lastly, rewind the unwound filament under tension.
The most important thing is to always hold the end of the filament under tension until it is either in your 3D printer’s feeder or attached to the side of the spool. The latter is accomplished by pulling the end through a hole in the spool or fastening it with tape or a filament clip.
To prevent the filament from jumping off the spool by itself, there are many individually designed solutions depending on the spool holder. This can be a clip-on holder with arms that prevent the filament from getting over the top of the spool or something similar. Check out Thingiverse for upgrades for your printer.
A tangled coil can occur once in a while, but with the right background knowledge, the problem can be quickly solved and easily prevented!
License: The text of "Filament Spool – Tips & Tricks Against Filament Tangles" by All3DP is licensed under a Creative Commons Attribution 4.0 International License.
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