Fw: Soundboard Compression & Cracks

[Erwinpiano]

  Hi Terry

   I like your questioning here on this topic.   It has been my experience
that when the compression board (or any board)was first made the rib ends
were free to bow in and out before glue in.  So here you have flat ribs now
significantly bowed because of compression.  Now glue that board in the case
and some of that crowning of the rib will stay there(or partially there) for
life even if the soundboard looks like a Venetian blind and has lost most of
its compression.
      i.e. it's the same as forcing a crown into a single rib with no panel
attached and gluing to the case.  The rib with its forced bow stays that way
once the glue dries.  Once a board is removed from the case the ribs return
to flat because of no residual compression to keep them bowed.  I've seen
this many times upon a boards removal from the case.
   Really in this instance if most compression is gone in the panel but yet
some crown is left then hey it has become a rib crowned board( at least
perhaps a little)

     And yes it's soooo interesting an I 'm guessing your life isn't all
that dull.
      Best

      Dale Erwin



----- Original Message -----
From: "Farrell" <mfarrel2@tampabay.rr.com>
To: <pianotech@ptg.org>
Sent: Sunday, June 10, 2001 6:31 AM
Subject: Soundboard Compression & Cracks


> Take a compression-crowned soundboard that is not collapsed (still has
some
> crown) that also has a few cracks through which you can see daylight. How
> can this be? The only thing that gives the board crown is the lateral
> compression across the grain as the wood gained moisture after its initial
> drying during construction. Now if you have daylight cracks in the board,
> does this not mean the board is not under compressional forces? Or is it
> that the inter-crack areas are still under compression from being glued to
> the non-dimensionally changing ribs (relatively speaking)? But then
why/how
> is it that one area of the board can be under compression and an inch or
two
> away, the board is under tension????????
>
> What is it about the soundboard that is soooooooooo interesting? Or is my
> life just that dull?
>
> Terry Farrell
>