Unusual rib structure?

[Keith Roberts]

Good question Ron. My guess is it's a compromise. If it was a structural
thing, wouldn't the stiffness of the rim and the ribs would make the board
too stiff ( too much impedance?) around the perimeter reducing the effective
area of the board? You might float some edges to gain back some freeness but
again it's a compromise. Ideally I think you would want the impedance of the
board to be in its operating range within an inch or so of the rim. No
tapering or feathering into the square footage of the board. A transition
point. Structurally I don't think that is possible because the point becomes
the weakest place of the rib. Thanks Ron, that's something to think about
that helps my understanding of the board. I think.

----- Original Message -----
From: "Ron Nossaman" <RNossaman@cox.net>
To: "Pianotech" <pianotech@ptg.org>
Sent: Thursday, May 08, 2003 5:17 AM
Subject: Re: Unusual rib structure?


>
> >FWIW - I've noticed on many boards that even when positive crown is
> >present, there often will be an inch-or-two wide swath of negative crown
> >adjacent to the rim. I guess from the ribs being thin there.
>
> I presume so.
>
>
> >I wonder what, if any, consequences there may be to this.
> >
> >Terry Farrell
>
> Probably nothing you can directly correlate to something you can hear,
> other than a general deterioration of the board. Which brings up a point
> I've wondered about for a long time. Why are ribs most often feathered
like
> that, regardless of whether the assembly is compression or hybrid
> compression/rib crowned? No self respecting structural engineer would
> design a controlled deflection load supporting beam that way. Too high
> stress concentration on the ends for the section profile. Very non-uniform
> stress distribution for something that's supposed to support a substantial
> load, perform dependably and last a while.
>
> Ron N
>
> _______________________________________________
> pianotech list info: https://www.moypiano.com/resources/#archives
>