Printrbot Jr. 40 mm Filament Fan... (Adjustable! :D)

by Welle417 May 14, 2013
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How does this help with jamming?

The longer your print, the more heat begins to creep up your extruder body and filament. Not so much with ABS, but with PLA it becomes maleable at a much lower temperature. As extrusion and retraction occur more frequently during a print, the more opportunity your filament gets to bend and crimp to the point of nasty blobs and bulges that cause jams.

This is an attempt at cooling the upper part of the extruder and dissipating that built up heat. Although this may not be as effective as a tubing/metal guide down to the hot end, I feel it will still alleviate some headaches.

I'm not so sure that the jamming problems are caused by heat. PLA goes through a glass transition (i.e. goes soft) at around 60C, and I doubt that the filament at the top of the extruder ever gets that hot. I had similar jamming issues and they went away completely by printing filament guides for the top and the bottom of the hobbed bolt (these ones: http://www.thingiverse.com/thing:60719)http://www.thingiverse.com/thi.... There is a lot of room for the filament to move around within the extruder, and I think what happens is that the filament moves (perhaps after a fast retract or something) and bends a little off-axis with the extruder. Further extrusion after this then exacerbates the bending and can even snap the filament before it gets into the extruder (I have found folded up filament at the top of the extruder many times after a jam). Maybe you could put that fan to better use as a secondary cooling fan for the extruded PLA. Hope this helps!

Printrbot Jr. Upper & Lower Filament Guides (1.75mm)
by phraust