Filament Knots on Spool

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Re: Filament Knots on Spool

Postby canadianavenger » Wed Apr 02, 2014 3:29 pm

The key here is keeping the filament under tension so the coils can't shift while on the spool. The "knot" is not a true knot as the end never passes through, but rather the coils become crisscrossed when the coils become loose, and effectively locking up when tension is re-introduced.

One solution here is to transfer the filament from the spool to a barrel cartridge. In the cartridge the filament is removed from the inside of the winding and works it's way out. As a result the coil is always pushing outward on the walls of the cartridge thus keeping the windings tight preventing shifting.

This is harder to do with a spool. You can increase the tension with the spool [thus keeping the filament in tension], but then you place extra load on the extruder, which is not ideal. With filament retraction and systems where the extruder moves relative to the spool this won't work, as the motion inevitably introduces slack into the filament, allowing for this type of tangle to happen. Another solution is to add a second motor as a pre-feeder [that only moves in one direction] that keeps the filament under tension on one side, and maintains a free open loop between itself and the extruder. A simple sensor set-up can be used to determine when the pre-feeder needs to advance more filament off of the spool.
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Re: Filament Knots on Spool

Postby orcinus » Thu Apr 03, 2014 7:46 pm

The thing i've mentioned i tend to do (i.e. cutting off just enough filament from the reel for a print or a few) actually helps prevent the tangles.

Or, to be exact, makes them non-critical.
Since the other end is loose, the filament is free to tangle / move the knot / disentangle as the print proceeds.

I've had it form a knot mid-air between my desk lamp and the printer, with the filament moving "through" the knot freely during the course of the whole print until it reached the end and untangled (when the print finished) more than once. It's counter-intuitive, but it works.
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Re: Filament Knots on Spool

Postby fma » Fri Apr 04, 2014 4:52 am

I broke a spool, some days ago, and this seems to be an idea: the spool is not balanced anymore, and keep the filament tight on one half turn, and then rleease it by the other half turn.

This is something to try, to see if it helps avoiding to tangle. Just add some weight on one part of your spool to unbalance it...
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