[Beowulf] A Cluster of Motherboard.

Jim Lux James.P.Lux at jpl.nasa.gov
Fri Nov 11 06:11:24 PST 2005

At 05:09 AM 11/11/2005, Glen Gardner wrote:

>I find it unacceptable to think that a machine shop is unable to make
>components to specifications.  I have worked in an engineering
>environment at all levels over the years and have had few problems with
>components being fabricated incorrectly.  As a rule,it is known how to
>do this stuff, and it is not exactly rocket science. Most small machine
>shops are well enough equipped that they can literally fabricate
>components for use in spaceflight (been there, done that). Cutting and
>drilling sheet metal to a drawing is not exactly a daunting, nor
>expensive task for them.

Not that a machine shop can't do it. Certainly they can.  I'm talking about 
using a hand drill and ruler and expecting to zap out 100 baseplates with 
tolerances sufficiently good that you're not going to be doing a lot of 
"slide the screw in the oversize hole til it fits" kinds of things.

Once you step into the machine shop realm, it makes little difference 
whether you're doing it yourself or contracting it out or buying it ready 
built.  The cost will be essentially the same.  All three alternatives have 
to invest capital in the machinery, spend money on maintenance, and spend 
money on salaries.  Leaving aside the "hobby cluster where you work for 
free", which is clearly not an apples/apples comparison.

>I do my own sheet metal work. Mostly because I know how and can cut out
>the middle man and save even more time and money.
>I simply do not see why this should be such a daunting task.  If people
>cant manage to use a pencil , hacksaw and a drill to make simple things
>then they might be better off buying commercially made hardware all the
>way and forget doing anything new and different... for the most part, I
>think that people have sufficient skill to handle the task.

I'd venture to say that for most people, if they are paying themself a 
reasonable wage, it's cheaper to have someone else do it, except for the 
smallest of scales.  The second you have to have "someone else" do it, all 
of a sudden you need to have a decent drawing (it can be a sketch, but 
you've got to explain it somehow), and you incur all sorts of things that 
consume time from not just you, but someone else too, and you've got to pay 
for it.  It's like software development.  Any one person can do pretty 
amazing things, but the moment a second person is added to the task, the 
KLOC/Hour rate drops, just because of the communication overhead.  Amdahl's 
law applies to machining as well as to software.

>The cost savings is there, and the advantages are significant... of
>course this is why people do sometimes stack bare boards to build

The "potential" cost savings are there.  I'd say that for a cluster of more 
than, say, 20 motherboards, being built by anyone where time is worth 
money, it's pretty hard to justify, until you get up to scales where you're 
basically manufacturing chassis, and the NRE is spread over enough boxes to 
make it small.

If you have an unusual packaging concern.. maybe it needs to be in a sealed 
box? maybe it has to fit into that antique grandfather clock?, etc. then 
you've got a case for custom design.



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