PERSONAL FAB
BY TOM OWAD
Three-Dimensional Printing Methods
3D printers print layer on top of layer,
slowly building a three-dimensional
object. A plethora of materials and
methods are used to build these layers.
The Stratasys Dimension is a commercial 3D
printer that uses ABS plastic. The ABS filament
comes in a self-loading cartridge, and is fed into
a heater block by two drive wheels. In the heater
block, the ABS is heated to a semiliquid state and
extruded through the tip, with layers as thin as 0.01".
The open-source RepRap ( reprap.org) project
uses similar technology. The filament is a polymer,
3mm in diameter. This is fed into a chamber, held
tightly against a drive screw. As the drive screw
turns, it pushes the filament down into a heated
barrel. The heat comes from a strip of nichrome
wire that is wrapped around the barrel. At the tip is
a nozzle with a diameter typically between 0.25mm
and 1mm (smaller is more precise, but takes more
time). A thermistor is embedded in the nozzle, so
it’s possible to adjust the temperature for different
polymers.
One of the easiest polymers to work with is
Polymorph, which is marketed as Friendly Plastic
or ShapeLock in the United States. Polymorph
extrudes easily, is relatively strong, and melts at
just 140°F. Unfortunately, it’s also expensive and
deforms if regularly exposed to temperatures
over 100°F.
RepRap enthusiasts have also experimented with
HDPE, ABS, and PLA (polylactic acid). PLA is the
most interesting, as it’s biodegradable and you can
make it yourself. PLA is formed by heating lactic
acid with stannous chloride; and lactic acid can be
created by fermenting milk or starch. The process
is sufficiently complex that it might not be terribly
practical in small quantities, but it opens up some
interesting possibilities for local production.
Another material the RepRap project has been
experimenting with is EcoComp UV-curable resin,
from Sustainable Composites Ltd. The resin is
158 Make: Volume 14
mixed with glass filler to make a paste, and hardens
when exposed to ultraviolet light. A ring of UV LEDs
mounted around the nozzle hardens the paste as it’s
extruded. EcoComp resin is made from plant oil, and
like PLA, will biodegrade if composted, making the
material carbon-neutral. EcoComp resin, however, is
very stable underground. If buried, it would actually
reduce the amount of carbon in the atmosphere.
The Fab@Home ( fabathome.org) project uses a
much simpler extrusion method than the RepRap:
the mechanism is simply a motor-controlled syringe.
A set of 30 syringe barrels and pistons costs $36,
so it’s easy to experiment with different materials.
This can lend itself to a lot of fun — peanut butter,
icing, toothpaste — if you can squirt it out of a
syringe, it’ll extrude. Making something sturdy out
Build one platform, and you
can experiment with everything
from cookie dough to laser
sintering.
of peanut butter might be difficult, but the fun is in
the experimentation. Betty Crocker Easy Squeeze
Decorating Icing works well and could be great for
3D decorations.
Silicone also works well in the Fab@Home. It cures
within 24 hours to a somewhat rubbery material. It’s
also possible to get conductive silicone, which enables
circuits to be embedded. For making solid models,
FabEpoxy, from Kraftmark, looks like the most promising material. It’s a two-part epoxy that is very durable
and machinable, and can be painted when cured.
All of these materials can be extruded at room
temperature, which significantly reduces their
complexity. Ironically, the Fab@Home syringe tool
is very expensive to build, because of the $130
linear motor that plunges the piston. That’s a lot of
