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RE: one word ..... plastics

Jeremiah,

Mark's suggestions sounds like a possibility - thermoplastics may be an
easier way to go with this idea of yours, unless you have access to an
injection molding setup (possibly a local technical college or trade
school?). The only problem that I see is the insulation from the CPU and
power supply and or internal cooling/heat evacuation, and the joining of the
seams.

Anyway, I do know that they make plastics and polymers like the kind Mark
mentions where you either have to superheat and mold them with a vacuum
device or apply a hardener resin. However, the last time I got a PET (Photo
Emission Topography) scan a few years back, they secured my head to the
headrest with a sheet of thermoplastic that was much easier to use (it
seemed). Basically, it was a 1/16" thick sheet of semi-flexible plastic,
approximately 10" (width) x 30" (length), and it had eye/nose/mouth holes
cut out of it. They dipped this sheet in boiling water and formed it around
my face and it hardened very fast (possibly less than a minute). This post
heating hardened state was much more rigid than when it was applied to my
face, but I'm not sure of the material's rigidity in it's original state. 

Afterwards, I had a nifty mask souvenir that was pretty durable, and didn't
seem susceptible to heat (as applied by a direct 100W lightsource at approx.
8" away). I admit however that it didn't stand up to the Bic lighter test. 

I would suggest that you speak with a radiology tech that works at a
hospital, or maybe try one of the medical supply company's on the web.

Cheers,
Tim

Tim M. King, Human Factors Engineer
Usability Engineering Services, A-3 02E30
Delta Technology - a Delta Air Lines subsidiary
voice: 404.773.8903     fax: 404.773.8865

-----Original Message-----
From: Mark Willis [mailto:]
Sent: Monday, December 06, 1999 3:12 PM
To: 
Subject: Re: one word ..... plastics

Some experience but it's been a while.  I'm in a bit of a hurry, I'll
try to help a little here.

There are various types/styles of plastics.

Thermoplastics can be heated (to soften them), then pulled/pushed into
the desired shape, and let cool so they set.  Usually a big pricey
Vacuum/Steam press or the like is used to heat and "convince" them to
move - you need a mold, either positive or negative.

Some can just be "hot glue gun" welded (The standard "hot glue gun"
sticks are a quite common plastic, you can form a case with a hot mold
and a hot glue gun & LOTS of glue sticks, or better yet a larger melter
<G>)

Some plastics are dissolved with solvents (like PVC plumbing pipe.) 
Some are glued, instead (Lexan? I think.)

Fiberglass could make a pretty nice case, if you can form a negative
mold, someone with a "chopper gun" could then spray this with gelcoat
and then later with fiberglass, you trim and finish it, should be fairly
cheap.  You could also lay down gel-coat, then brush resin in there and
add a few more layers of glass cloth and get a fairly strong, thin case,
stronger than with a chopper gun, just not as quick!  And a lot
messier;  You have to work to remove bubbles etc.;  I've made canoes
with others' help, in the garage, that way, it's a bit of work but the
results are *strong* (We'd have lost a chopper gun canoe in one mess-up
we hit, it would have crushed, not bounced, off a rock in the Skycomish
river here.  Did mess up the gel coat!)

A positive mold, for those not "in the know", is a plug that'll fit the
inside of your desired box;  A negative mold, would fit outside the box,
you then brush your box's body inside the mold.  (You DO get a good,
"perfect" outside the box with this method, which was why I mentioned
it;  If finish is a "Not Care", you coulduse a positive mold, it's
faster to work with, but the end gelcoat is uglier and so on.)

Hmmm, could you just Fiberglass over that metal case?  <G>

Cheapest is to find a case that's already existing, of course;  I've
seen a few cases made of PC board material, even, with wood corners for
rounding.  Pretty good EMI on those <G>

If you can find a local plastics and/or fiberglass shop, and talk to the
workers there, they should be able to help you figure out how to do what
you want to do, learn about the way you plan to go first, though.

  Mark

Jeremiah T. Isaacs wrote:
> 
> so, I am about to venture into the world of custom plastics and dont have
> a clue.  I just know that for my case I need a plastic shell. (it will be
> an outer plastic shell on top of an inner metal case for the boards and
> drive)
> 
> if anyone has gone down this path, has any resources they could point me
> at, 'twould be appreciated.
> 
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