Page 62 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

Chapter 2 Materials: How to Choose and Where to Find Them 43

Thermoplastic materials can be molded and remolded when heated, and will return to
original form. This quality makes thermoplastics, like soda bottles, recyclable.

Thermoset plastics cannot be remolded and thus can’t be recycled. Examples are
bowling balls, football helmets, and epoxies.
As with all materials, plastics come in a variety of shapes and sizes. The following are
some common types and uses (thanks to Peter Menderson and his materials class
notes and resources at http://itp.nyu.edu/materials/):

• ABS is tough and impact-resistant. A lot of small appliances are made from
this. It’s softer than acrylic and easy to machine. It’s what LEGOs and the
original printing material used for Makerbot’s CupCake CNC are made of.
• Acrylic (trade name Plexiglas) is a clear, hard plastic commonly used in laser
cutters and model making. You can cut thin sheets just by scoring it with a
hobby knife and then snapping it apart.
• Delrin is tough, easy to machine, and low friction (although not as low as
Teflon). It is used commonly in gears and bearings.
• Nylon is similar to Delrin and good for general-purpose wear applications.

• PETG bends easily and is a cheaper alternative to polycarbonate.
• Polycarbonate (trade name Lexan) is shatter-resistant, has excellent clarity, and
has high-impact strength. It is porous, so it will absorb moisture from the air.
• Polyethylene comes in a wide range of grades and properties. It also vacuforms
well (see Chapter 9 for a description of vacuum forming).
• PVC plastic is the white material usually used for plumbing pipes and fittings.
Although easy to saw, cut, and drill, it is particularly environmentally unfriendly
because of toxins released in its manufacture and disposal. You cannot laser
cut it, and you should use safety gear (mask, goggles) even when cutting or
drilling it.

• Styrene is easy to machine, low cost, and flexible. It comes in thin sheets that
can be cut with a sharp knife.
• Teflon is slippery, so sheets and tubes are used for bearings and sliding surfaces.
• Rubber parts are used as shock absorbers and stoppers, as well as in O-rings
and gaskets to seal mechanisms from the elements.