Slightly OT: tips for fabricating with plexiglass?

From: Doc Shipley <doc_at_mdrconsult.com>
Date: Sun Jan 16 14:56:45 2005

Computer Collector Newsletter wrote:
> It's only "slightly" off-topic because what I'm building is a new case for my
> Apple 1 "Replica 1" board.
>
> I've heard some horror stories about whole (expensive!) sheets of plexiglass
> simply breaking in half when incorrectly drilled through. The guy at the
> plastic supply company tried selling me a special drill bit, but I'm hesitant
> about that. Does anyone has hands-on experience and tips (vs. just
> speculation) about working with this stuff? This computer will be on display
> as some public events, so the final appearance is very important.

   I've never seen Plexiglas shatter or split, but small cracks in the
corner of a cut or radiating from a drilled hole is very very common.

   Plexiglas is a nightmare to machine. That includes drilling, cutting
to size, sanding, everything. It's very subject to stress fractures,
which means you have to cool your cut and cut very slowly and evenly.
Unless you're very good with a hand drill or have a drill press, I would
recommend Lexan instead.

   If you do use Plexiglas, there are some things you need to do:

Have some spare drill bits, saw blades, etc. You'll probably dull some,
and cutting with a dulled bit is very likely to cause cracks.

Cool the cut with water or a light soap solution. This reduces stress
during the cut, and also carries away the fragments as you cut.

   Polish all cuts and radius all edges. By "polish", I don't mean
"make it shiny again", but remove any tool marks and ridges, and sand
the corner off the edges. Any sharp corner, inside or outside, is a
"stress relief point". Sounds like a good thing, right? but stress is
relieved by cracking at that point.

   If you're bolting this piece together, or to another assembly, use
some kind of rubber/plastic grommet at attachment points. Even with a
good cut and good finishing, the stress of tightening screws against the
Plexiglas is still risky. Even a stiff "nylock" washer is better than
nothing.

   I'd use Lexan if at all possible, or just build a metal or plastic
case with viewing windows. If you do that, you can use clips or
adhesive to hold the Plexiglas and not worry about drilling at all.


        Doc
Received on Sun Jan 16 2005 - 14:56:45 GMT