PSN-L Email List Message

Subject: Re: Lehman base material?
From: ChrisAtUpw@.......
Date: Tue, 18 Jan 2000 20:32:29 EST

In a message dated 13/01/00 09:23:33 GMT Standard Time, twleiper@........ 

>> My daughter's Lehman is on a pier cast atop what is either an immovable 
huge bolder or exposed bedrock in the root / wine cellar. It is a very stable 
environment with natural temperature control and the seismo is made from 
thermally stable materials, such as a granite tool and die makers slab for a 
base. With a natural period of 50 seconds it only needs seasonal centering 

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? I read through your account of 
the construction of the original seismograph with interest. 

    I have been trying to think of a relatively cheap, heavy and robust base 
material for a seismograph. I noted that people who used plate Aluminium 
seemed to have put weights on them, so presumably, some weight can be an 

    I was driving past some roadworks yesterday, when I had a bright idea. 
You can get 2" thick paving slabs made out of high density 'vibrated' 
concrete, with a reasonably flat finish on both sides. The workmen were 
cutting 3' x 2' slabs to size with a disk as I passed and I wondered if 
anyone had thought of using part of one for a seis base? You could probably 
stick flat metal base plates onto the concrete with epoxy. The smallest 
diamond core drill that I can hire is 1/2", which seems a bit too big. I 
haven't yet tried drilling a slab with a hammer drill and a carbide bit, but 
from past experience, high silica aggregates are quite drill resistant. 

    Do you know if anyone has used a paving slab and if so, were there any 
problems? The price and weight seem about right. Can you comment, please, in 
comparison the granite block?

    Regards, Chris Chapman


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