high physical density cluster design -structural...

[Fitch, Chester]

> Cost of aluminum at a retail stores adds up fast .... and 
> welding is tricky as
> you need an inert atmosphere.  If you use mechanical 
> fastners, you need to
> machine holes (punch, drill press, etc.).  OTOH, we have made 
> some very nice
> cabinets with riveted aluminum and angle extrusions ....
> 
> surplus steel (3/4" box is ideal) can be very cheap and you 
> used to be able to
> get a High School shop class to do the welding for free ... 
> They might have the
> stuff need for sheetmetal work also.

Check around - you can usually find a local surplus/scrap/odd-piece dealer
in aluminum (or steel) who is MUCH cheaper than retail.. Several months back
I was able to obtain ~40 square feet of scrap (but unused) 3/16 inch
aluminum plate for about $80.00 US. (They sell it by weight) He even cut it
for me to my rough measurements for $20 -- saved me a day with a saber saw,
that did... well worth the cost. Ended-up with about 12 shelves for a
cabinet rack - MUCH cheaper than buying standard, prefabricated shelves. Had
I gone retail, I figure the aluminum itself would have cost me about 10x as
much (even if I'd even been able to locate/order it)...  He had lots of
other extruded metal parts cheap, as well... 

Pays to look around..

I would stick with aluminum - steel is much harder to work with, and you
shouldn't be using the case to ground the units anyway... Strength is not
really an issue either, if you use aluminum that is reasonably thick, or
fabricate the case properly. (I assume we're not talking several hundred
pounds here) No need to weld the aluminum - easy enough (most times) to just
drill holes and use extruded shapes and fasteners (bolts and/or rivets) to
fabricate any shape (case) you need.. Get a little creative, and you
wouldn't even need the prefabricated stuff (like UniStrut).. Depends on how
fancy you want to be, and the weight involved, of course. 

I shudder when I hear people talking about using some kind of wood (or even
plastic) for the case: having overloaded my fair share of circuits over the
years, I want NOTHING combustible near such a beast - A system melt-down is
one thing, but what you DON'T want is a case that could catch fire at the
same time -- you could loose the building its' in as well...  Any competent
electrician looking a such a beast would have a fit.  While such a
posibility is admittedly unlikely, why take the chance?  Metal may melt, but
at least it won't catch fire!

(Sounds a bit paranoid, I know, but...  just my $.02)

Good luck! 

Chet Fitch

----
The superior programmer uses his superior judgment to avoid situations
requiring superior skill. (Or the fire department)