Soundboard 60-ft. Arc

[Farrell]

Thanks Ron. I am indeed aware that there are dozens of other factors
involved (not that I understand them very well YET), I was just trying to be
sure that I was able to make whatever curve I chose. Thanks.

Terry Farrell

----- Original Message -----
From: "Ron Nossaman" <RNossaman@KSCABLE.com>
To: <pianotech@ptg.org>
Sent: Wednesday, January 16, 2002 8:47 AM
Subject: Re: Soundboard 60-ft. Arc


> > On a five-foot span I get 0.63 inches of crown.
> >This seems excessive (isn't an unstressed new board supposed to have
about
> >1/4" - 3/8" of crown in the middle?).
>
> Your crown height for 60' radius is right by my figures, but how long a
rib
> do you plan on having in a piano? That's what cutoff bars are for. The
> compression crowned boards ended up averaging about XX crown at XX length
> (varying widely with material choice and methods) as a consequence of the
> crowning process rather than a design criteria. With rib crowning, you are
> granted the opportunity to make your own decision and build to a much
> closer spec. It's supposed to be whatever you find works to your
> satisfaction with all the other dozens of factors considered in your
> soundboard design, string scaling, bridge configuration, loading, etc. Nor
> is it particularly necessary or (to some builders) desirable to have the
> same crown radius throughout the rib scale.
>
>
> >Or is it that on the rib-crowned
> >board, you cut the rib to the aforementioned arc, glue it to the board in
a
> >caul of the same arc, and when removed from the caul the naturally flat
> >board help the assembly to straighten out a bit to where it has the
> >"?normal?" 1/4" - 3/8" of crown?
>
> Panels are still dried down before assembly in a rib crowned board, just
> not as much as with compression crowning, so the panel is still under some
> compression, and still helps support crown rather than dragging it back
down.
>
>
> >Am I making a boo-boo somehow with my drawing?
> >
> >Terry Farrell
>
> Nope, but there are a few assumptions behind it that you need to decide
> whether or not to accept. <G>
>
> Ron N