There’s a way to very easily untangle knotted filaments, according to ToyBuilder Labs’ Joseph Chiu.
Knotted filament is perhaps one of the most annoyingly common issues facing those using personal 3D printers. Here’s what happens: the end of the filament has somehow slipped underneath one of the strands circling the spool. Then, perhaps hours into a print operation, the filament becomes knotted up and printing fails as no more filament can be pulled into the extruder.
It’s very annoying because it’s often an invisible problem (you can’t always see if a spool is knotted) and delayed (the printer failure occurs long after you start printing).
In this video Joseph Chiu explains an incredibly simple technique for fixing the problem: just push the offending group of strands off the spool and wind them up again. Watch the video to see how it’s done.
We’d add that best practice would be to ensure you NEVER leave a spool with a dangling end. ALWAYS tie up the end so that it cannot silently slip under another strand when you’re not paying attention. Most spools have a small hole or similar mechanism for securing the end of the filament as shown here. Use them!