Rib Dimensions

[Delwin D Fandrich]

----- Original Message -----
From: "Phillip Ford" <fordpiano@earthlink.net>
To: <pianotech@ptg.org>
Sent: July 22, 2002 11:15 AM
Subject: Rib Dimensions


> In an earlier post about rib tapering Del said that he thinks that the
> 'typical' feathering at the ends of ribs evolved as a result of necessary
> building practice for compression crowned soundboards.  I wonder if bridge
> dimensions evolved the same way?

I've no knowledge of how bridge dimensions evolved. Certainly they were some
smaller in fortepianos without iron framing. I would guess they reached
their present height and width (neither of which are exactly standardized)
by the simple structural necessity of holding the bridge pins and the
physical necessity of spanning the gap between the soundboard and the string
plane.


> What is desired is light but stiff ribs.
> Structurally speaking, the dimensions that would most efficiently result
in
> that would yield a rib that is narrow and tall.  But the typical rib is
about
> as wide as it is tall.  Do you think this was to provide enough glue area
to
> keep the rib attached to the board when building a compression crowned
board?

Depends on how the soundboard is crowned. In a compression-crowned
soundboard the ribs must remain flexible enough to be forced into a crown by
the expanding soundboard. In these systems the ribs actually resist the
formation of crown and fight it for the duration. In a rib-crowned
soundboard system the designer has a few more options. And, yes, gluing area
does become an issue if the ribs are made too high and too narrow.

Del