techfortrade's Thunderhead PET Filament Extruder Technical Feasibility Study

techfortrade has written a Technical Feasibility Study about their work designing the Thunderhead PET filament extruder for the ReFab Dar experiment.

Work on the Thunderhead Filament Extruder originally started in 2014 when
techfortrade contracted Matt Rogge to further develop work that he had started in
2012, to design and build a low cost ‘appropriate technology’ filament extruder that
could be used in community settings in low income countries to produce 3D printer
filament for local use from waste plastic collected by the community.

The first extruder was deployed in Oaxaca Mexico in collaboration with a team from the
Oaxaca FabLab and was designed to process High-density polyethylene (HDPE). It was
vertically oriented and driven by a drill motor. The machine was low cost and produced
filament that could be used for printing, but HDPE was abandoned due to difficulties
printing with this material. Acrylonitrile butadiene styrene (ABS) was the next material
that the machine was modified to extrude. A fume hood, diameter sensor and
automatic spooler were added. After achieving the production of usable filament, this
material was also abandoned when it became apparent that it would be difficult to
source a supply of flame retardant free ABS in the locations where the extruder would
be used.

As a result and by a process of elimination, Polyethylene terephthalate (PET) became
the target plastic for extrusion and the ReFabDar project provided an opportunity to
test the design revisions already underway to support the extrusion of PET. Since the
deployment of the Thunderhead PET extruder at STICLab in Dar es Salaam in January
2016, all components of the machine have undergone several design revisions. The
machine has been run vertically, horizontally, with and without a water bath etc. PET
has proven to be a much more difficult plastic to form into a consistent filament.