Managing your filament

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The 3mm filament used in the Mk2 extruder is generally extruded for us from CAPA or PLA by friendly companies that make plastic welding rod for car repairs. They extrude it into coils or onto spools for shipping - usually coils which come inside a plastic bag.

As the extruder slightly twists the filament clockwise when viewed from above, the spool or coil needs to be free to rotate around the axis of the filament to avoid extreme kinking. Depending on the material and your luck, this rotation may break the filament, or send it in clinging spirals into the innards of your RepRap - even worse, onto the bench!

The approach here was developed for coils, but similar tactics would work well for a suspended spool.

First, do not remove the coil from its packaging until you need it. The filament picks up atmospheric moisture in humid conditions, which forms bubbles of steam as the molten plastic extrudes. With this approach, you only make a small hole in the bag to extract the end from the centre of the coil. This hole is reinforced with gaffer tape. A single crossover wrapping of tape is put around the bag to reinforce it. Imagine you're wrapping a parcel with a bit of string. On the side opposite the hole, tape on a stiff wire loop from which the thing can dangle from swivel clips.

Use two swivels just to be sure, or a short length of ball-chain. Support the coil either from a ceiling hook or from a crosspiece attached to two uprights. The uprights extend about 750mm above the X axis to give room for the extruder to move around underneath. If your extruder rotates the filament particularly frantically, ensure that the corner of the suspended bag occasionally touches the nearest upright. This will prevent the spool acquiring momentum - which can snap or distort the filament.

PLA feeds best if lightly lubricated. Basically, just contrive to pass the filament through a lose knot in an oily rag. Ordinary SAE 30 oil, the stuff you use on hinges and the kid's bike or "3-in-1" type products are fine.

-- Main.VikOlliver - 15 Dec 2007

Further reading