A question was raised by Mr. Tuttle regarding Delrin.  Delrin is the
trade name of a hard plastic made by DuPont.  I quote from a recent
Small Parts, Inc. catalog:

        "Delrin is a useful replacement for metal in many
        applications such as gears, pulleys, impellers, etc.
        Delrin is easily machined with all standard machine
        tools.  Its machinability is equal to or better than
        free machining brass in the normal operations of mill-
        ing and turning to threading and tapping.

        "Delrin offers a high degree of toughness, impact
        strength, dimensional stability. low coefficient of
        friction and fair chemical resistance."

I have used this material as a replacement for bronze bushings with good
results.  Also, I used it as a substitute for brass in a part that
normally would be plated, but which I didn't have the inclination to
plate (a non-standard tuba mouthpiece).  Their claims of impact strength
are not exaggerated.  That mouthpiece has taken blows which would have
junked a silver-plated brass mouthpiece.  Delrin seems hard like a
thermosetting plastic, but I am not sure whether it is thermosetting or
thermoplastic.  Nonetheless, this hardness lets it take a nice finish
with little effort.

Hope that this helps you out.
Dave Vincent