Soundboard drydown for installation, was installation with hide glue

[Richard Brekne]

Hi Mike.

Me too.  I suspect some of it will have to do with the idea that the 
tight fitting rim will have some form of support for crown and that if 
you have a reasonably tight fit with a dried assembly it will expand 
into the rim... which of course will resist.

I know Hamburg puts their assemblies into a hot box just before 
installing into the rim and attaching the bridge.  Tho they do not dry 
out their panels prior to ribbing to more then around 5.5% EMC.  What I 
was told was that the ambient RH they held in the soundboard room and 
much of the factory was all the drying they subjected their panels to 
prior to ribbing. They used crowned ribs but the assembly crowns further 
when they taper the rib ends... so I suppose this means they are using 
curved cauls as well.

It has always struck me tho that once the ribs are on... the outer 
perimeter of the assembly is more or less fixed.  If both sides of the 
assembly expand upon taking on humidity... then at least some of the top 
part of the ribs would have to also expand... as in some degree of 
horizontal straight line tensioning of the ribs in addition to the 
tension the top half of the ribs take on as part of bending.  My 
understanding is that the ribs tension strength exceeds the compression 
strength of the panel to do this... but I could be wrong.  It certainly 
is strong enough to bend them and introduce at least the tension that 
accompanies that.

Cheers
RicB



        Richard, I'm glad you asked that.  I too wonder why.  Once the
        ribs are
        on, I can't rationalize a benefit to taking the board outside of
        the
        normal range of (controlled) workshop humidity for installation
        in the
        piano.  Not that I would be surprised to learn of several good
        reasons
        for doing so.  I hope you get some interesting answers.

        Mike


    Richard Brekne wrote:
     >
     > On a general note.. this raises an issue for those of us with less
     > experience installing soundboard. Under what circumstances would one
     > dry out the ribbed assembly for installation in the case ? All
    panels
     > regardless of how crown was achieved ? Whys, whats, and wherefors
     > appreciated.
     >
     >