You asked about making your own plastic cases.

The first and easiest way is to just buy a case from
somebody who makes a general-purpose product. There
are a variety of people who make molded plastic
shells in all sorts of configurations. You can get them
with battery doors, openings for displays, button holes
and suchlike. They're not as cheap as a custom-built
box in volume, but for small quantities they work fine.

If nobody makes a case that will work for your application,
your next best bet is probably sheet metal. You can have
a metal box made for fairly low cost, so long as you don't
do anything too complicated or tricky.

If you *must* have plastic, another method is vacuum forming
of ABS sheet stock over a mandrel. A wooden pattern is
carved, which forms the interior. A sheet of ABS plastic is
heated by radiant coils, then draped over the pattern while
a vacuum is drawn on the pattern side. The air pressure
forces the hot plastic over the pattern to make the shape. It's
limited in size, depth of draw and corner filling, and may
require significant post-machining to make a usable part.

Still another method is casting. You can carve a wax master part
and use a silicone rubber mold process to create a rubber
mold. After cutting open the mold and extracting the master,
you re-close the mold and pour in a pre-mixed resin-and-catalyst
plastic and allow it to cure. You'll use a vacuum draw to
extract the bubbles from the liquid plastic before it cures,
and may also apply heat to initiate the curing.

Instead of resin, you may do the casting process with a hot
wax injection, then use the wax as the basis for a lost wax
casting in a flask. This can give you an aluminum casting
for not-too-much money. Or sterling silver, if you prefer. :-)
Or gold, if you're *really* wealthy. Jewelers use this
technique, but it doesn't work too well for really large
objects.

If surface finish is not critical, a sand-casting process can
give you very low-cost aluminum castings from easily-built
wooden patterns. It's very coarse; certainly not suitable
for a consumer product without substantial hand-finishing.
You have some limits on the shapes you can produce, too.

A machinist can make a box out of plastic by directly machining
it, or you can take sheet stock and glue it together and sand
it to shape, or you can model it on a 3-D CAD system and
have it built on a stereolithography system.

Or you can, as you say, 'build a mold' and pour in plastic.
As always, the devil is in the details......

Mark G. Forbes, R & D Engineer  |  Acres Gaming, Inc.    (541) 766-2515
KC7LZD                          |  815 NW 9th Street     (541) 753-7524 fax
forbesm@peak.org                |  Corvallis, OR 97330
http://www.peak.org/~forbesm
mforbes@acresgaming.com

"There has been an alarming increase in the number of things I know nothing
about."
---Anomalous