Hi Rick, Hay Jan-- call me kuz we need to talk.

Rick,  I designed my Lehman base because I wanted to use some scrap aluminum
plate I got from a salvage yard that was kind of small. It needed to be
bolted to something because the unit would not have worked if It wasn't. The
mass would have just sat on the ground after the pipe uprights tipped
forward.

I settled on the 50/50 cement sand mix because that is what my dad taught me
to use some years back for making castings. During the PSN meeting Robert
Uhrhammer, of the Berkeley Seismological Lab mentioned that the Broadband
network uses a 50/50 mix as Jan just posted earlier and they just sit their
equipment on the slabs. He also said they sometimes just sit them on window
glass to eliminate even more expansion. It turns out that a 50/50 mix has
the best stability / expansion ratio due to the ratio of elements and
density. He also said they never use any ag-rock in it. Of course I just
knobbed my head in agreement as Bob explained all this and acted like I
always new that... and told myself something about having dumb-luck.

All in all, the design works real well for me. I was even able to put a
second slab around the mounting cube and keep an air gap between them so I
could stand next to the device and work on it without too much extra effort.
Later, I also added 3-inch insulation to the sides and tops of the covers. I
only checked them from time to time after that through a window in the top.
About once a year the upper wire would rust and break and about every 2-3
months I would tweak the 4-40 screw to center the boom. By the way, I think
I said this before, did I mention SPIDERS!!! Never just reach down into the
darkness... One night I came up with the biggest blackest angriest fattest
spider at the end of my elbow you ever saw.
Regards, Steve Hammond PSN  Aptos, California
-----Original Message-----
From: Rick Bitto 
To: PSN-L Mailing List 
Date: Tuesday, January 18, 2000 5:54 PM
Subject: Re: Lehman base material?


>I had thought of pouring a concrete base from scratch with threaded
>inserts cast in place.  I too was wondering what drawbacks this base
>would have (other than weight).
>
>Rick
>
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