Rib Tapering

[Farrell]

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Hey Richard,

I'll stick my neck out - not that I am any authority at all on this =
subject - but perhaps it will stir something up. I figure if I say =
something outrageous enough, then someone that knows what they are =
talking about will chime in.

On a compression crowned soundboard, like a Steinway, the rib acts as =
something to keep the one side of the panel from expanding when the =
panel takes on moisture upon removal from the hot box - that is what =
makes the panel crown. The ribs will be of constant thickness so that =
the soundboard develops crown evenly. The ribs are thinned only at the =
end to keep the soundboard flexible at the perimeter.

A rib crowned soundboard will have ribs that are more evenly tapered =
over most of their length, such as the taper you describe. That is =
because such a shape better supports a load when applied to the middle =
of the rib, such as downbearing on the bridge. That is what I think, but =
you'd really need input from an engineer type to say more about that =
subject.

Now all other manufacturers use the Steinway-shaped rib because that is =
what Steinway does.

Is your soundboard crowned? Compression crowned? Rib crowned?

Terry Farrell

----- Original Message -----=20
From: "Richard Brekne" <Richard.Brekne@grieg.uib.no>
To: "Newtonburg" <pianotech@ptg.org>
Sent: Friday, January 23, 2004 10:18 AM
Subject: Rib Tapering


> Ok soundboard makers of the nett... Question.
>=20
> I have re-ribbed this old square grand soundboard, and used more or =
less=20
> the ideas Joe and I exchanged, and I am ready to finish off the ribs=20
> now. On most of these oldies the ribs are very gradually thinned from=20
> the middle to the edges of the board. On newer instrument types the =
ribs=20
> are the same thickness  for most of the width of the panel, then =
tapered=20
> suddenly.
>=20
> So... what is the functional difference and what would be the=20
> recommended type of tapering for this case. It is a very low tension=20
> affair and probably will not be able to exert so very much down =
bearing=20
> if that means anything.  If I had to hazard a guess I'd wonder about =
how=20
> tapering effects the flexibility at the edges. But thats just =
guessing.
>=20
> First time out with a soundboard rebuild.... finally have my =
fingernails=20
> a bit dirty with this kind of work. So any good advice is muchly=20
> appreciated. The panel was dried for 2 weeks in my shop to the lowest =
RH=20
> we get in these parts... roughly 26 %. The panel is about half the=20
> thickness of a modern panel, and the ribs in question are about 1 cm=20
> thickness, 2 cm wide, and 2 of them are 60 cm long the third about 45. =
I=20
> can post a picture if that would be of help.
>=20
> Thanks muchly
>=20
> RicB
>=20
> _______________________________________________
> pianotech list info: https://www.moypiano.com/resources/#archives
> 
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