[geeks] Plasic casings

[David Cantrell]

On Mon, Jan 21, 2002 at 02:10:09PM -0500, Kurt Huhn wrote:
> Don't get the plastic too hot, or it can melt and bind to the mold.  Not
> pretty, or easy to remove.  Steep angles and corners are also very tricky,
> from what I've been told.  Dunno how you'd make a box, but I suppose it
> could be done in pieces and welded together...

Tight angles can be done, but only with thin sheet.  So to make a tight
angle in a thick sheet, cut a V in it so you end up only bending a thin
section.  For strength, you should then melt the two sides of the V back
together or use glue.

The reason is that when you bend a thick sheet, the middle of the sheet
stays the same length, the inner side of the bend is compressed, and the
outer side is stretched.  Most plastics are good in compression.  Most
plastics are lousy under tension.  It will tear on the outer side.  Then,
once the tear has started, the high forces at the tip of the tear will
cause it to propogate through the sheet very quickly, and it will snap
at the bend.  You can get away with it in thin sheets, because then there's
not much stretching to be done.

When the original poster was talking about encasing their SBC in plastic,
I assumed he wanted to melt plastic around it, just like a fly embedded
in a piece of amber.  I doubt that the components would like the heat
much :-)

-- 
David Cantrell | david at cantrell.org.uk | http://www.cantrell.org.uk/david

      Blessed are the pessimists, for they test their backups
                                            -- anon