Restoring crown in old soundboards

[Delwin D. Fandrich]

----- Original Message -----
From: "Isaac OLEG" <oleg-i@wanadoo.fr>
To: "Pianotech" <pianotech@ptg.org>
Sent: Wednesday, April 16, 2003 11:18 AM
Subject: RE: Restoring crown in old soundboards


> Hi Del,
>
> ANd what about gluing back (partly) the soundboard and the ribs wedged
> a little apart of the belly. Was aid it can produce a little crown
> from treble to the killer zone - but it for sure seems a lot of
> uneasy work to me (unglue, push toward center, glue back.
>
> Forcing the ribs may well give them a tad of resistance is not it ?

Very little, if anything, will be gained by doing this. Any crown obtained
will quickly dissipate as the string load is applied.

The problem is not with the rib-to-soundboard gluing or with visible cracks
in the panel. The problem is that the wood cells in the original soundboard
panel have been damaged beyond repair by years of compression stress. Unless
you can figure out a way to restore the original resiliency of the wood
cells you simply cannot obtain the amount of stress interface between the
panel and the ribs necessary to form and hold crown. Even if you were to
completely remove the original panel, glue it all back together, dry it down
to 4% moisture content (just like it was when it was first bellied), and
then reglue it to either the original ribs or to a new uncrowned rib set, it
would still not achieve anything like its original crown. Under this set of
conditions it might develop some small amount of crown (depending on just
how badly damaged the wood cells are) but it would be minimal and weak. It
would not support much string bearing and it would soon be flat once again.

Del