Klarinet Archive - Posting 000322.txt from 2002/12

From: "Dee D. Flint" <deehays@-----.net>
Subj: Re: [kl] WOO HOO!
Date: Thu, 12 Dec 2002 18:44:43 -0500

----- Original Message -----
From: "Jeremy A Schiffer" <schiffer@-----.edu>
Subject: Re: [kl] WOO HOO!

> On Thu, 12 Dec 2002, Roger Shilcock wrote:
>
> > Rebecca's R13 pretty certainly has been impregnated with oil already.
Whatever
> > the effect of oiling the *bore* miught be, it can hardly influence the
chances
> > that the instrument might crack.
> > Roger S.
>
> This would most likely be correct. While moisture absorption could play a
> role in cracking, most of it is going to be related to standard thermal
> shock functions - the expansion and contraction of the wood due to heating
> and cooling.

Actually if you calculate the forces generated in wood by thermal expansion
and contraction, they are insufficient to crack the wood unless of course
the wood has an unseen flaw. In which case it will crack sooner or later
regardless of the thermal effects.

The effects of moisture loss and gain result in far larger dimensional
changes (and thus stress) than result from thermal effects.

>
> Regardless of
> age, rapidly heating and cooling any substance - wood, ceramics, etc. -
> increases the likelihood of cracking. That's why sidewalks are made of
> separate sheets of concrete (usually 3-5 feet long); the gaps allow the
> concrete to expand in the heat without cracking. For a great demonstration
> of this, place glass marbles (like you played with as a kid) in boiling
> water for a minute, then immediately transfer them to ice water. Just
> don't use valuable ones...

While this is true, every material has a different coefficient of thermal
expansion. Thus one material will easily survive a temperature difference
that will destroy another. Just because one material cracks at certain
conditions, doesn't mean they all do.

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