Piano Rims (rambling post)

[Phillip L Ford]

>>
>> How do the rim braces fit into this? I've heard it said that they are only
>there to
>> keep the belly rail from rolling.
>
>This is one of the primary functions of a good rim bracing scheme. At least
>it should be, though often it's not. The typical S&S rim bracing scheme
>(including its many clones and semi-clones) does nothing to stabilize the
>belly rail in the upper tenor/treble section and is a contributing factor in
>the short sustain time of these designs through the upper tenor and lower
>treble.
>
>A well-designed rim bracing scheme, of course, will also serve other
>functions. It should stiffen the long bass side which can get pretty floppy
>even with a fairly massive rim assembly. It should provide mounting points
>for the various nosebolts. 

Do you think it needs to be wood?  Why do you think
many makers settled on softwoods for the braces?
I noticed that the Walter grand has maple braces.
I've seen a piano with a cast iron bracing system
that was bolted to the inner rim.  Do you think
there would be a disadvantage to metal?

>The function of the cast gray iron bell used in
>the larger S&S pianos could probably be better served by a bellybrace
>extending from the inside curve of the inner rim to the bellyrail. A
>nosebolt could still be used to mass couple the plate to the brace. Nothing
>would be lost and much would be gained.

Do you think that the bell puts any rolling preload
on the rim or resists the rolling or twisting of the
rim caused by soundboard vibration any more
effectively than a rim brace would?

Also, slightly off the subject, but do you think a
heavier plate in this area or a rib on top of the
plate could as effectively do the same thing as the
nosebolt?
>
>> Perhaps you could have the soundboard resting
>on
>> a thin knife edge around the perimeter, as in a guitar or violin.  Why
>would this
>> be a bad idea?
>
>I'm not sure it is a bad idea in and of itself. The design of the soundboard
>itself would also have to change. The soundboard system used in the 'modern'
>piano is essentially a clamped-edge, two-dimensional wave-carrying vibrating
>panel. What you are describing changes this to an essentially hinged-edge
>... vibrating panel. Obviously, the edge stiffness of the panel will change
>considerably.
>Del
>

If what you want is the entire soundboard moving up
and down as a diaphragm it seems to me that having
this hinged edge attachment might come closer to
giving that than a clamped edge arrangement.
Actually building something workable might be
difficult.

Phil F


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