Jim,

You didn't mention Aluminum, which is my favorite.  With wood, I'd be more 
concerned with its response to humidity, which can be extremely large.

It's largely in the vertical designs where thermal effects are most severe, 
and there  the main problem is not thermal expansion, but the change in 
spring stiffness (elastic modulus), about 20x larger than the expansion 
number.  A good feedback design can greatly reduce those thermal effects.

There had been some testing being done on a graphite leaf spring, but I 
haven't heard anything recently.

Regards,
Brett


At 11:07 AM 1/25/2009 -0800, you wrote:
>I'm a newbie and have never built seismometer.  I'm wondering why
>steel is used so much in seismometer construction when other materials
>have much less thermal expansion.  Spruce wood, for example, has about
>1/7 the thermal expansion of steel.  Other materials expand even less,
>quartz, graphite, some glasses and ceramics, etc.  Some of the
>materials with low CTEs (Coefficient of Thermal Expansion) are
>expensive (invar, tungsten, polyimide, diamond), but others are
>affordable.  Spruce is inexpensive and widely available.  Here are a
>couple of sources of graphite rods and other shapes:
>http://www.waleapparatus.com/catalog.asp?prodid=548212&showprevnext=1
>http://www.graphitestore.com/items_list.asp/action/prod/prd_id/25/cat_id/22
>
>Simax glass is cheap and has an extremely low CTE.  I wonder what kind
>of seismometer a good glassblower would make?
>
>Jim Turner


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