Unusual rib structure?

[Delwin D Fandrich]

----- Original Message -----
From: "Farrell" <mfarrel2@tampabay.rr.com>
To: "Pianotech" <pianotech@ptg.org>
Sent: May 09, 2003 3:14 AM
Subject: Re: Unusual rib structure?


> Del wrote:
>
> "I prefer to terminate the ribs about 10 mm inside the inner rim for at
least the half of the rib set."
>
> Why 10 mm gap? What is your preference for the other half? - rib goes
right up to rim? - rib overlaps rim? Why? Is it OK to have all ribs
terminate without overlapping rim?


I like the outer perimeter of the soundboard assembly to be relatively
flexible throughout the bass and lower tenor region. Hence the 10 mm gap.
(There is nothing magic about the 10 mm--it's just a safe amount.) Up into
the tenor/treble other factors come into play. With a so-called "solid"
board there is always a region along which the grain of the soundboard
panel roughly parallels the inner rim. This area is prone to cracking
unless the ribs continue on over the inner rim. And, from this region on
up, the assembly can generally use the added stiffness contributed by the
overlapping ribs.

Del