Soundboard drydown for installation

[Richard Brekne]

I tend to agree Jude.  That said... seems pretty clear to me that Rons 
experiment shows rather conclusively at least three things.  One, that 
the immediate reaction of the soundboard to downbearing is for the edges 
to pull away from the rim. Two, that the soundboard taking on humidity 
will attempt to grow outwards above the center line of the assembly... 
and a tight fitting rim will resist the thing crowning .... not aid.  
Three that the edge wood of an assembly is considerably stronger then 
has been loosely suggested many a time on this list.

I still think the whole thing functions more like a cable supported arch 
then anything else.  The ribs do indeed experience tension as the panel 
takes on humidity. Both from bending and no doubt some small amount of 
absolute tension.  That is to say the entire rib will be more lean more 
towards the tension side of the balance between tension and compression 
then a similar rib that is simply bent would.  The more you compress the 
board either by increasing downbearing or by letting the assembly take 
on humidity... the more tense the <<cable>> becomes. That will continue 
until such point as the panel itself experiences compression failure.

Cheers
RicB



         > The only purpose of that model was to illustrate that
         > soundboard crown isn't an end buttressed arch, which I think
         > it did well enough. What else would you expect or wish a
         > larger and more complex model to show?


    I guess I'm not thinking about a different model but rather a
    different experiment. I'll get back to you when I finally pose a
    real question. :)

    Jude Reveley, RPT
    Absolute Piano Restoration, LLC
    Lowell, Massachusetts
    (978) 323-4545