PSN-L Email List Message

Subject: Re: Lehman base material?
From: twleiper@........
Date: Wed, 19 Jan 2000 18:49:03 -0500

On Tue, 18 Jan 2000 20:32:29 EST ChrisAtUpw@....... writes:
>In a message dated 13/01/00 09:23:33 GMT Standard Time, 
>Dear Mr.Leiper,
>    This all sounds great, but what is the price of granite 
>engineering slabs 
>and how do you go about boring holes in them?


In my case the price was ten bucks many years ago at a scrap yard. It is
two by three and 4" thick
and already had the leveling mechanism. All my attachment points are with
PC-7 epoxy, so
no drilling was required. The idea was to preserve the geometry of the
components to the
most rediculous degree possible over long term temperature drifts
(days/weeks). I had tried
all manners of insulation, stratified heating elements, baffles, etc.
with less than ideal success.
In addition, there is a principle in amateur seismology that states that
the more you make the
instrument immune to the environment, the more it is immune to YOU.
Trying to experiment with
it, ie; uncovering, adjusting, restabilizing and analyzing, becomes more
of a pain in the ass. 

Since my vault is highly stable, I decided to focus primarily on reducing
drafts (relatively simple) and
preserving geometric integrity over long period temperature swings
through materials selection. I am
experimenting with bimetallic boom and support elements and hope to be
able to preserve the geometry
(and adjustments) over a twenty degree differential. I'll post something
if it leads to anything worthwhile.

One thing I would suggest if you don't have a complete machine shop in
the garage...Make everything out
of sealed particle board and other composites. My brother has a very high
end custom furniture manufacturing
operation in San Diego, and his tolerances with this material are getting
down to the thousanths, and it is
extremely stable. Like the Dobsonian telescope mount compared to an
elegant German Equatorial mount, it
promises excellent performance at a price attainable to the masses.

I think my next project will be a complete seismometer and recorder
constructed entirely off materials
available at Home Depot and Radio Shack, so that great silent majority of
teaming millions who want to
become amateur seismologists can realize their unfulfilled dream...


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Larry Cochrane <cochrane@..............>