[Beowulf] A Cluster of Motherboard. - tray

[Glen Gardner]

Autocad is hardly tricky. Most machine shops will fabricate aluminum to
0.005" tolerance if you do not specify otherwise, so you have to allow
for tolerances... oversize holes, etc.  This is not a problem in
fabrication.  A skilled person with a hand drill can often fabricate
more precisely than 0.005", down to nearly 0.001" with some care. 

A CNC machine can typically set to within 0.005 mm after warmup, so
drilling holes precisely enough is not an issue for cnc.  I think that
you will find that motherboards are typically fabricated to anywhere
from 0.005" to 0.010" tolerance, and some of the cheaper board houses
will fab to 0.015" if you don't specify tighter tolerances.   They can
all go down to better than 0.001", but they usually don't like to
because it costs a lot more in setup time and materials wasted due to
rejects. The problem there is the tendency of glass-epoxy laminates to
change their dimensions under pressure/heat over time.


Glen


 
On Fri, 2005-11-11 at 17:21 -0800, Alvin Oga wrote:
> hi ya andrew
> 
> On Fri, 11 Nov 2005, Andrew Piskorski wrote:
> 
> > The very sturdy 18" x 26" 16 gauge aluminum cookie trays (sheet pans)
> > are $9 each,
> 
> you can get customized flat metal for about that same ( $10-$15 ) costs
> too if you did all the work ( measuring and generating a usable autocad
> drawing that they can plug into their cnc machine )
> 
> 	- for the guy that wondered how come people can't draw
> 	autocad drawings properly for mounting a motherboard,
> 	it is in fact very tricky business ... as tolerances
> 	is measured down to 0.001" and  if its a little off, some
> 	of the nuts/standoffs can ruin their expensive equipment
> 	or more realistically, your 1U power supply will not properly 
> 	fit into the 1U chassis without stretching/bending the metal
> 
> 	- drawing (random/close enuff ) lines and circles and bends is
> 	trivial ...
> 	doing it properly requires prior experience with the target
> 	sheet metal shop machines and k-factors and material thickness
> 	and hardness and other whacky stuff including thickness of paint
> 
> 
> for the shelf ..
> i'd bend a couple ears for rackable mounts ( ie rack shelf with holes for
> motherboard )
> 	- but that bend for the ears will add a few bucks to the costs
> 
> it'd look "better" than the cookie tray ??
> 
> the fun for the cookie tray method is to have it like a blade,
> that it plugs in and power up by itself .. no cords/wires other than 
> ethernet, and even that can be plugged into a custom nic-backplane
> 
> we've been debating doing that cookie-cutter drawing ( shelf w/ ears
> and holes ) and gpl' the sucker even so those of you with (cnc capable)
> sheet metal shops can make your own shelf
> 
> c ya
> alvin
> 
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