Compression Question

[Delwin D Fandrich]

----- Original Message ----- 
From: "Richard Brekne" <Richard.Brekne@grieg.uib.no>
To: "Pianotech" <pianotech@ptg.org>
Sent: August 29, 2003 11:40 AM
Subject: Re: Compression Question


>
>
> John Patton wrote me a year or so back when I asked him about this and
said
> then that Steinway dries their boards down to about 4% and uses machine
> crowned ribs. FWIW.

That is, then, a change from their traditional "perfected" practice.


>
> Do I understand correctly that the rib crowned board will sooner or later
also
> surcomb to more or less the same self destruction, but that essentially
it will
> just take much more time for it all to happen ?

Sigh. It depends on the MC of the soundboard panel at the time it is
ribbed. If it is 4%, yes, the panel will still self-destruct even if the
ribs are crowned. But the system will still retain most of the crown that
was machined (or otherwise put) into the ribs. If the MC of the panel was
up around 6.5% or 7% when it is ribbed it will still be possible to damage
the board by leaving the piano in a semi-truck trailer somewhere in
Tennessee during a summer heat wave for two weeks (every day well above
100º F) while the driver goes on vacation but it is far less likely that
the panel will be damaged during anything resembling normal climate
conditions.

Never is a long time and even wood beams stressed in thier longitudinal
direction will undergo some creep or compression set. At least in theory.
But, assuming a normal string load, after some initial settling it will not
be all that noticable over the lifespan of the piano or its owner.

Del