Klarinet Archive - Posting 000713.txt from 1998/09

From: Edinger/Gilman <wde1@-----.com>
Subj: [kl] heat expansion
Date: Sun, 20 Sep 1998 14:53:18 -0400

When I wrote that a metal ring was analogous to a cross section of a
clarinet bore, I meant in shape only (and that's still not quite right -
the ring is doughnut-shaped and the bore is cylindrical). However, as
others have pointed out, the inner wood does not "expand" inward as it
is being warmed - that would be contraction, not expansion: the
molecules would be getting closer, not farther apart. In contrast,
would they move outward if they were being cooled? No, the inner bore
still expands outward; and the outer wood on the surface also expands,
but if it expands too fast, rather than evenly, the weakest points in
the fibers would separate, and - voila - a check and eventually a crack
form. Wood tissue is considerably less uniform than cast iron rings,
and its various components (e.g., different kinds of cells and
compositional polysaccharides) are going to have different coefficients
of expansion. Considering all the possibilities of natural variations
and injuries over the decades of its growth, it's to be expected that
potential weak spots would be present, invisible to the naked eye.
Maybe X-ray analysis would find the weak spots, but it would be darned
expensive, and probably not worth the cost compared to occasional joint
replacement.
A chimp banging a stick on the tree in 1875 may have caused the injury
that cracks somebody's R13 in 1998. Or a lightning strike, or a drought,
or flood, or whatever. These are living systems, and you can't take
anything for granted with living systems. It ain't benchtop wet
chemistry. Think of cracks in your instrument as allowing you to be
personally touched by the life of the tree it came from ; - ). My money
is on the already-expressed opinion that cracking is most likely
"kismet," i.e. if the flaw is grown into the wood, it's going to express
itself sooner or later, and if it's a uniform, flawless piece of wood,
you won't have any problems (like Nancy Buckman's instruments - sorry
Nancy, I couldn't resist). Now, in those pieces with lesser flaws (and
you can't know until it cracks), it's best not to take any chances with
sudden temperature changes (such as heating the inside too fast for the
outside to catch up). You might play a lifetime with an instrument that
a less careful person would have destroyed, or you might simply have a
joint that's going to crack no matter how you treat it. So treat it so
that you can blame Mother Nature rather than yourself, and if it cracks
anyway, go read about Zen philosophy.

Bill Edinger (who's been both careful and lucky since 1967)

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