Soundboardcrown

[Delwin D Fandrich]

----- Original Message -----
From: "Peter Kestens" <peter.kestens2@pandora.be>
To: <pianotech@ptg.org>
Sent: December 16, 2002 12:45 PM
Subject: Soundboardcrown


> Collegues,
>
> I've build my first soundboard and I have to say, It looks very good.  I
> also glued the (flat) ribbs on and gives a crown, about 3/8 inch by
> bending them, during gluing, with an compressed air press.  But a week
> later, I could not place the board in the piano earlier, the crown
> diminished and the board returned to be as good as flat.  My question
> is:  is this normal or what is the cause.  And is there somebody who can
> tell me how much crown he gives and what's staying after a week, month
> (I mean the board only stocked in the shop, not placed in the piano).
>
> Thanks a lot for the replies.
>
> Peter Kestens


There is not much information to go on here, but...

I'm guessing that what you are seeing is normal compression set taking place
inside the soundboard panel. And in all probability your next step will be
trying to figure out how to get those ribs off the soundboard without
damaging the soundboard panel. Then figuring out how to repress the thing so
that you will end up with some long-term crown in the assembly before you
glue it into the piano.

If you put no crown in the ribs, where did your initial crown come from?
What was the moisture content of the soundboard panel when you glued the
ribs on? Is your soundboard press curved? If so, what is the radius of the
curve?

Typically, if you are going to depend on just the curve of the
rib-to-soundboard press to form your crown you would want to end up with a
whole lot more than 3/8" crown (on the longest ribs) when it comes out of
the press.

This is why very few, if any, shops attempt to crown soundboards in this
manner.

Del