On Wed, 12 Nov 2003 05:50:30 GMT, "john moorhead"
wrote:

I picked up a sheet of plastic ~1/4 thick for use as part of a fence and for
shielding, and I am wondering if I got the right stuff...

You got the right stuff.

It'll be either acrylic (Lucite / Perspex / Plexiglass) or
polycarbonate (Lexan). In 1/4", either is reasonable as a woodworking
guard.

With practice, or some comparison pieces, scratching the surface or
bending the sheet will let you "feel" the difference between the two.

1/16" thickness needs to be polycarbonate, as acrylic would be far too
brittle. In 1/4" though, either works. Polycarbonate absorbs more
energy on breaking. If acrylic cracks, then it'll suffer a brittle
failure and crack right the way through. Polycarbonate is also less
susceptible to failing around a scratch or crack causing a stress
riser.

Polycarbonate is softer though (so watch for scratches) and it has
problems with chemical exposure weakening it. It's also flexible,
which can be either good or bad, depending on how you design the
guard.

I generally use acrylic, or polycarbonate in thin sheets if I want to
bend a smooth curve. A good source for thin polycarbonate is
replacement visors for face shields; they're cheap, and you don't have
to buy a big sheet.

--
Die Gotterspammerung - Junkmail of the Gods