Tuesday, July 29, 2008
Making CAPA Filament
I created this:
It's basically the high pressure screw driven syringe with changeable nozzles. A nut is soldered into one end of a piece of plumbing pipe, and a pipe connector to the other. The wood contains a captive nut, a washer is soldered to the threaded rod to form a plunger, and the handle at the top is turned to force the plunger down.
The pipe is then dipped in boiling water for a few minuites so the CAPA melts, then the handle can be turned and this happens:
The nozzle I'm using has a 3mm hole in it, which created a filament of 3.4-3.5mm (pretty good consistency). I'm going to try making a nozzle between 2mm and 2.5mm tomorrow and see if I can get a 3mm filament.
See more pics on flickr
Keep in mind that extruded diameter is probably a function of extrusion speed as well, so keeping that constant may give you more consistent results.
1. a longer barrel.
May have problem with friction
2. motorised piston going back and forth, with a hold in the side to feed in plastic from the hopper.
Getting a bit complex
Switching to an electric heater could work too, as my hot water method only gets the plastic to < 100^C, at which point the CAPA is still very thick
I wonder if we could make a continuous process out of this somehow...
Perhaps some sort of centrifugal pump (http://en.wikipedia.org/wiki/Centrifugal_pump) with a hot impeller? The granules would be slowly droped (manually or automatically) in the center of the impeller, would slowly melt, and then be pumped out through a hole. We'd have to find a way to keep friction down between the molten plastic and any stationary sides of the pump, but maybe it could be done?
One issue that is raised whenever someone has ideas for an extruder is air bubbles becoming trapped, how 'bad' (or good) has this been with your design?
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