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Subject: Re: Lehman base material?
From: Keith Payea kpayea@......................
Date: Wed, 19 Jan 2000 18:25:46 -0800

I've used a similar tactic, making the base of my STM style vertical unit out of
garden variety (literally!) 8" x16" x2" concrete stepping stones.  I used three,
cut one in half, and made a 24" long base out of two layers of 1 + 1/2 pieces.  I
used "liquid nails" as an adhesive and it works great.

For fasteners, I mostly used "T-nuts" epoxied into holes in the concrete which I
made with ordinary masonry drill bits.  I chose mostly #8 hardware, and it turned
out that a 1/4" drill bit was just about perfect to drill a hole to glue the
T-nut into.  I found that the drill bit wants to wander as you drill, so I shoot
for a slightly sloppy fit.  Then, I fill the holes about half way with epoxy and
set the entire assembly to be attached, with the t-nuts threaded on, right into
the holes.  I use wax paper to make sure only the t-nuts get epoxied to the
base.  In five minutes, the epoxy is set and I back out the screws and remove the
assembly.  I usually clean up the epoxy overflow with an exacto knife, and wait a
full day before putting any real strain on the fitting.

It makes the base heavy, but extremely heavy!  One other note.  Concrete is
porous, so before final assembly, I coated the entire base with a high quality
sealer/primer paint.  It has the benefit of making the base a nice neat white

Good Luck,

    Keith Payea

ChrisAtUpw@....... wrote:

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