Jim,
Regarding your questions of June 27:

As I have often said before, I don't think that there is anything
particularly special in the dimensional selections for the STM-9
vertical seis. I suppose I could say that my design is mostly intuitive,
based on many years of experience. Essentially, I started out with 
a leaf-spring, added a mass and a boom to connect them, which required 
hinges for the boom and flexures for the spring, etc. And it works with 
a self noise level and stability much better than I anticipated.

Regarding the square tubes that are part of the spring clamp: 
the idea is to apply a firm continuous termination of the stresses
across the end of the spring, rather than just a few screws.
I also thought it would avoid thermally sensitive micro-stresses
that a row of screws would create. It seems to work. If I had a mill,
I would consider milling an 0.018" slit lengthwise through the center 
of a 1/4 " brass bar for the ends of the leaf spring; the 0.010 slits
at the ends for the flexures would have to be at a right angle to the
slit for the spring.

I attached the flexures to the brass bars by means of centered slits 
in the 3/16" bars for several reasons (compared to soldering them to
the side of the bar): it is much stronger; it dosn't apply any torque
to the bar; it is much more creep resistant, etc.
The slits are easy to do with a 0.010" jewelers saw blade available
at True-Value stores. I use a jig to get it centered and square.
THe brass cuts like butter when making such a fine slit.
When I solder in the bronze flexures, I am careful to apply the heat
(from a small torch) only to the brass bar itself so as not to soften the
temper of the flexures. If the flexure strips DO get heated, I restore
the temper by immediately spraying them with water.

I did some evaluation of the braided stainless fishing leader, but it presents
problems in fastening it to the bars. Feeding it through a small hole in
the bar and crimping a band (from the crimp part of a connector pin) on 
the ends seems to work. THen it is epoxied into the hole under tension to 
prevent micro-positioning noise. I did not use this flexure in a completed
seis yet, so I don't know how it compares noise-wise to the flat strips.
But I may have to use it to work up an alternative to the "Lehman" design
that uses only taught wires for the boom suspension (using guitar strings.)

Regards,
Sean-Thomas


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