On Tue, 05 Nov 2013 12:26:16 -0600, Tim Wescott
wrote:

I was going to say "acrylic", but then I realized that maybe I would be
narrowing it down too much.

How hard is it to machine a part out of hard clear plastic and then make
it clear again? Any gotchas? What plastic should one start with? What
question am I failing to ask?

The part will be cylindrically symmetric (i.e., turned on a lathe), about
1.5" diameter, 0.5" tall, and accuracy can be as sloppy as 0.01 in all
directions. But it would need to be "pretty".

Some plastic that is a bit more rugged in impact than acrylic would be
nice (do they make crystal clear Delrin?) but I can't think of anything
like that which would actually work in this case.

I've gotten pretty good finishes on acrylic (Lucite, Plexiglas, etc.)
using Hangsterfer S-500 coolant mixed about 1:10 with water, eitther
flood or mist. A squeeze bottle or aspirator (like window cleaner
bottles) would probably work pretty well, too.

Here's the result from one of my earliest trials:

http://memweb.newsguy.com/~mphenry/DiskFinished-2.JPG

Sharp tooling helps and you want a fairly fast feed to avoid melting
the chips to each other or the milled surface.

Mike