Killer Octave Question

[Delwin D. Fandrich]

----- Original Message -----
[link redacted at request of site owner - Jul 25, 2015]
To: "Pianotech" <pianotech@ptg.org>
Sent: Friday, April 11, 2003 7:40 PM
Subject: Re: Killer Octave Question


>
> Owen wrote:
>
> Ron,
> Would gluing on an uncrowned long bridge not force some of the valuable
> and available crown out of the rib/board assembly?
> Owen Greyling, RPT Ontario, Canada
>
> Owen,
>
> Your right, it would. I have noticed this while building soundboards. If
> the bridge is flat it fights the crown of the ribs as it is clamped into
> the case. I am  no scientist and I don't have a degree in engineering
> but it seems perfectly logical and consistent to machine the bottom of
> the bridge to more or less follow the crown created by the ribs. I would
> think this would add to the overall strength and durability of the whole
> soundboard. I don't know what it does to the tone but a soundboard that
> lasts longer will sound better longer.
>
> I have worked on many brands of grand pianos and have observed that some
> pianos seem not to have this feature but the two brands that
> consistently show evidence of bridge crowning are Steinway and Mason and
> Hamlin. Newer ones will have more crown than old ones indicating that
> the crown does dissipate over time but not as fast as the ribs. Large
> pianos have a much more noticeable amount of crown than the little pianos.

I think I don't understand something here. "Newer ones will have more crown
than old ones indicating that crown does dissipate over time..." OK so far.
Basic compression set from Wood Technology 101--the soundboard panel can't
take the perpendicular-to-grain stress. That's what I've been telling folks,
lo, these many years. Then, "...but not as fast as the ribs." Assuming the
soundboard panel, the bridges and the ribs are all still glued together they
are going to pretty much have to lose crown together.

All other factors being equal, large pianos will have more noticeable crown
only to the extent that the soundboard is larger and the crown is more
easily seen. Given soundboard panels of equal thickness, ribs of equal
cross-section and an equal starting moisture content (assuming a
compression-crowned soundboard system) the resulting crown radius will end
up the same. The size of the piano, as such, is not a factor.

Del