rib glueing

[Delwin D Fandrich]

----- Original Message -----
From: "Garold Beyer" <garbey@wingsisp.com>
To: <pianotech@ptg.org>
Sent: January 09, 2001 4:01 PM
Subject: Re: rib glueing


I might as well comment on the other two points...

>
> >If you induce a curve to two thin pieces of
> >wood and glue them together in the curved state, >THEY STAY CURVED.
Unless
> >piano soundboards follow some other natural >principals, my guess is that
> >is DOES matter.
> >Terry Farrel

This would be true only of they are glued up with the grain of the two
pieces of wood parallel to each other. If they are glued up cross-grain (as
is the case with the soundboard assembly) the final curve is not a fixed
curve, but a variable one depending on the MC of the two pieces of wood.

>
> PTJ, 7/87, page15 "Incidentally, it does no good at all to have a bellied
> press and then use flat ribs; if you aren't going to crown the ribs, you
> might as well use a flat deck and cook the board a bit more."
> Jack Krefting

I disagreed with this statement in 1987 and I still disagree with it. If all
other factors are the same -- MC, flat ribs, etc. -- the panel glued up in a
curved caul is going to end up with more final curvature, regardless of the
final MC of the soundboard panel. A result you may or may not want.

There seems to be a belief among some that if compression-crowning is
obtained by pressing flat ribs against a panel using a curved caul instead
of by super-drying the panel and pressing flat ribs against a panel using a
flat caul/surface that the result is somehow not compression-crowning. But,
it is.

Del