Klarinet Archive - Posting 000692.txt from 2001/04

From: "CLARK FOBES " <reedman@-----.com>
Subj: [kl] Response to Dee regarding cracks
Date: Sun, 29 Apr 2001 03:03:17 -0400

I wrote:

> ... Cracks occur because of different expansion rates at the bore and the
> surface of the clarinet. The most common cause of cracks is a blast of
warm
> air (breath) inot the bore when the instrument is extremely cold. The
> outside cannot expand as fast as the inside and the instrument will crack
at
> it weakest point. This is usually between the top two trill keys.

And Dee repsonded:
This simply isn't true. I've run the numbers and it's not the temperature
gradient. Wood has a strength of 1000 psi in its weakest direction and is
several times stronger in other directions. The amount of stress due to
thermal expansion if the outside of the horn is at 0°F and the inside is at
100°F is less than 100 psi, far below the amount required to crack the wood.
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. In these
instances, even bumping the instrument will break it if it's bumped in the
"right" direction.

Now humidity is another story entirely. Water cause extreme swelling of the
wood. Dryness can cause extreme shrinkage of the wood. Water has an
extreme expansion and contraction rate with temperature and has been known
to crack rocks.

Dee,

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.

Clark W Fobes

---------------------------------------------------------------------
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