Klarinet Archive - Posting 000695.txt from 2001/04

From: "Daniluk, Bill" <bdaniluk@-----.com>
Subj: [kl] FW: [kl] Response to Dee regarding cracks
Date: Sun, 29 Apr 2001 07:51:24 -0400

I have neither 25 years of engineering experience, nor world renown as a
repair person, but is it not possible that both of these knowledgeable
individuals are correct? It does seem intuitive that if a steep
temperature gradient alone could cause an instrument to crack, there
would be a lot more cracked clarinets (given the marching band example
below) than it seems there are. If the sharp temperature gradient would
only cause a crack if there were some material flaw, would not the
constant expansion/contraction of the change in humidity over time tend
to excacerbate a minor (non crack causing flaw) to the point where a
sudden temperature change would cause the crack to occur?

Just askin'
BD

-----Original Message-----
From: Dee D. Hays
Subject: Re: [kl] Response to Dee regarding cracks

----- Original Message -----
From: "CLARK FOBES " <reedman@-----.com>
Subject: [kl] Response to Dee regarding cracks

> I don't know what your qualifications are as a repair person and i am
not
> certain what you mean by "run the numbers". Cracks occur when
clarinets
are
> played cold. I have pinned many, many clarinets that have cracked
under
this
> condition. Oboes are notorious for cracking when played cold. In the
few
> seconds it takes for a clarinet to crack I doubt that it would
absorb
> enough moisture to cause the crack. Almost without exception the
clarinets
> i have pinned cracked under consitions where the player was outside or
the
> room or hall were cold. You also stated that "The exception would be
if
> there is a pre-existing flaw that couldn't be seen creating either an
> unusually weak spot or a stress riser".
>
> This is exactly the problem. The area between the two trill key tone
holes
> is very weak and prone to cracking. If you think cracks can't occur
when
> clarinets are cold because it is theoretically impossible then you had
> better make another type of investigation based on empirical evidence.

I am an engineer and have done quite a bit of work on stress in my 25+
year
career. When I say "run the numbers," I mean calculated the strength
and
calculated the stress. A special interest of mine has been thermal
failure
and fatigue (i.e. failure due to stresses induced by temperature
gradients).
Now an interesting thing is that material thickness has no bearing on
the
stress resulting from thermal effects. Only the temperature, material
properties, and stress risers are relevant.

Empirical evidence? Simple, if it were temperature, almost all wood
clarinets subjected to the cold would crack not just an occasional
instrument. There has to be some other factor. There have been far
more
that did *not* crack than did. I belong to a generation where a large
number of students had used wooden student horns and marched with them.
And
this was in Iowa winters, not Florida or some other benign climate. I
marched many a football game with a wooden horn where the temperatures
were
below freezing.

As a long time engineer, I've seen too many cases where what "everyone
knows" as based on empirical evidence was wrong. This leads to
solutions
that don't work because the root cause is identified incorrectly. Or it
leads to no effort to find a solution as people may view the problem as
unsolvable. We could undo history and go back to the caves by
eliminating
every in our lives that "everyone knew" was impossible.

Dee Hays
Michigan

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