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Originally Posted by mechanicalbrain
I've been planning my summer project and I started getting into material selection. The main thing I'm having trouble with is picking plastics, something I really have no experience with.
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This is how you get experience. It is smart to ask.
There are MANY options available, well under your budget.
Plastics are rated and compared in many ways, but your application only depends on a few of these characteristics: strengh, weight (density, actually), machinability, and coefficient of friction
Look at
www.mcmaster.com and type in "plastics" in the search area. The resulting page will provide general descriptions of common plastics.
I am guessing that Acetal (commonly known as Delrin), Nylon, and UHMW would be your best materials to use. Each of these are fairly hard and will be slick wheels, unless you put some sort of treads on them. Polycarbonate will be a bit stronger, but also more expensive.
If I had to pick one plastic to work with for machined robot parts, it would be Acetal (Delrin). From McMaster, you can get a 1 foot bar of 1"x1" stock for $11 and change.
<edit... crap, I misread mech-brain's notes, and did not realize his needs were for a 1 ft x 1 ft piece... see other suggestions below for cheaper materials>
Good luck,
Andy B.