Soundboards/stress, questions

[Richard Moody]

Another factor regarding moisture is that boards tend to warp across
the grain.  The direction of this warpage can be predicted by which
side the board is "up". The illustrations in wood working books
illustrate this . Thus they can in warping break away from
the  ribs from their middle or their edges.  Wood shrinks also across
the grain with dryness, another cause of cracks. However 'cured' wood
shouldn't do this. But with alternating periods of humidity and
dryness, cracks from shrinkage might be more common.  .
	The load or pressure on the sb from the strings, I was told amounted
to a small elephant standing on it.  Another source said 1,400 lbs.
(either a small elephand or a large cow) Would like to find the
formula to compute this.  Must have something to do with vectors.  
	Would also like to know if the ribs are bent before glued to the
sb.if they are glued to a already bent sb, or if sb and ribs are
glued together then bent together.  Probably different for each
manufacturer? 

Richard Moody 
----------
> From: rhohf@idcnet.com
> To: pianotech@ptg.org
> Subject: Re:  Soundboards/stress
> Date: Thursday, June 12, 1997 7:26 AM
> 
> There have been a lot of interesting and thoughtful ideas in this
thread.  One 
> of the things that makes this business so fascinating is that we
have been 
> making soundboards for centuries, but the fundamentals are still so
poorly 
> understood:
> 
a soundboard with ribs attached 
> is a complex system containing tension _and_ compression.
> 
> 
> All of my comments refer to unloaded soundboards.  So what does
loading do to 
> the stresses?  Applying downbearing does not simply put the board
into 
> compression:  if it did, boards would not crack. 
> 
> Bob Hohf
> Wisconsin
>