Klarinet Archive - Posting 000729.txt from 2001/04

From: "Lacy, Edwin" <el2@-----.edu>
Subj: RE: [kl] Cracking clarinets
Date: Mon, 30 Apr 2001 13:39:19 -0400

> Are newer instruments more prone to cracking than older, more conditioned
horns, [.....]

Once again, observation might lead us to conclude that newer instruements
are more likely to crack. However, it is probably the case that if a wooden
instrument is going to crack, it is more likely to do so when it is new. In
other words, the fact that much older instruments rarely seem to crack may
not be due to the fact that they are more conditioned or "broken in," but
because the wood itself was relatively free of weak points.

I've been hesitating to say this, because this always results in major howls
on a list, but there is a major problem with the theory that heating the
bore causes cracks by creating stresses when the wood of the bore tries to
expand while the cooler exterior tries to remain at its original size. That
problem is that when the wood of an instrument expands, it doesn't just
expand outward; rather, it expands in all directions. Thus, when the wood
expands, the bore of the instrument gets smaller; when the wood contracts,
the bore gets larger.

I know what is happening right now. Many people on the list are saying,
"Everybody knows" that this isn't true. However, you don't have to take my
word for it. Check with anyone who has had training in materials science.
This is considered axiomatic in that field.

Want a simple proof? Imagine a small cylinder of a material, such as
grenadilla wood. Now, imagine that a thin disk is sliced from the cylinder,
so thin that the the thickness is negligible. Now, consider what will
happen when the wood expands. It will expand in all directions, from the
center toward the edges, so that the circle becomes larger.

Now, imagine a "doughnut" of the same material, large enough so that a thin
slice can be cut that will be the same size as the other disk. Now, again
imagine the material expanding. What happens? The material again expands
in all directions. In other words, while points on the outer diameter are
expanding outward, points on the inner diameter are expanding toward each
other, or inward.

The "doughnut" is analogous to a slice cut from a clarinet. (Warning:
Don't try this on your good clarinet.)

I think I know what the next question is: What happens if only one side of
the disk is heated so that it alone expands. The answer is, that portion
that is heated expands outward. So, if it is the bore of a clarinet that is
heated, the sides will tend to expand toward each other.

The next question would be, Wouldn't there be stresses created on the radii
of the disk, between the heated and unheated portions? I think the answer
is yes. The thing to be determined would be how severe the stresses were.
But remember, we would be talking about stresses on the lateral axis of the
instrument rather than the longitudinal one, which is not the kind of crack
that a wooden instrument is normally subject to.

Ed Lacy
**************************************************************
Dr. Edwin Lacy, Professor of Music
University of Evansville
1800 Lincoln Avenue
Evansville, IN 47722
telephone (812)479-2252; e-mail: EL2@-----.edu
**************************************************************

---------------------------------------------------------------------
Unsubscribe from Klarinet, e-mail: klarinet-unsubscribe@-----.org
Subscribe to the Digest: klarinet-digest-subscribe@-----.org
Additional commands: klarinet-help@-----.org
Other problems: klarinet-owner@-----.org