[pianotech] re-fabricating a failed soundboard

[Joe Goss]

Humm,
Is it the board that has lost compression or the ribs.
Joe Goss BSMusEd MMusEd RPT
imatunr at srvinet.com
www.mothergoosetools.com
----- Original Message ----- 
From: <jim at grandpianosolutions.com>
To: "pianotech" <pianotech at ptg.org>
Sent: Monday, May 28, 2012 7:39 AM
Subject: [pianotech] re-fabricating a failed soundboard


> >That's been acknowledged a lot of times here. The part of the question
> that's left out is what type of construction is being used. Countless
> compression crowned boards failed since being built. If these boards
> being discussed required re-ribbing and insertion of strips of old
> spruce to compensate for the compression set that didn't happen  and
> take them back to full width from which they mysteriously presumably
> shrunk somehow, they were apparently among the failed. Reproducing the
> conditions under which the original failed with the original material
> seems to me to be rather optimistic and not really paying attention.
> 
> 
> Right. But it should be noted here that the technique was demonstrated 
> in the context of a conservation of historic fabric seminar.
> 
> My interest here was not in suggesting that this technique as a way to 
> make or replace boards. I don't even buy into the notion that these 
> reconstituted boards are precisely the board and sound these historic 
> pianos had when new...actually, as someone coming out of the historic 
> conservation world, I find that despite whatever conservation method was 
> used, that the result is still wildly speculative. I'm not interested in 
> basing my designs on speculative information. My take is that we really 
> will never know what the original pianos sounded like, except in very 
> broad strokes, like sustain time.
> 
> Rather, my interest was in the panel itself as as a substance. I was 
> curious to see what resilience was left in a panel which had experienced 
> compression failure. Not the board as a structure, as we know that's 
> failed, but the panel wood in and of itself.  Is there any resilience 
> left?  It does seem that there is, as when the old ribs are steamed off, 
> the panel, though shy of the original width, still was being restrained 
> by the ribs. They reported that the wood, freed of the rib restraint, 
> expands somewhat.
> 
> However, when they steamed the sucker to get the ribs off, the EMC 
> changed, so at what EMC was the expansion measured...don't know...
> 
> But on the other hand the panel was capable of opposing the reglued 
> ribs, so there is cellular viability left in the aged compressed wood.
> 
> In any case, just take the panel. How would the aged wood with cellular 
> damage at least at the edges, sound like, if used as a panel substance 
> in a new ribbed/designed structure.   My hunch is that the panel, having 
> a different resilience profile than when new, would be stiffer than new, 
> though still resilient.  Carbon fibre, laminated boards, etc are 
> alternative panel substances which work as panel substances. I wonder 
> how aged compression beat up spruce, as an alternative panel substance 
> would  perform?  Again, panel as a substance only, not part of the 
> original compression crowned structure.
> 
> Jim Ialeggio
> 
> 
> 
> 
> 
> -- 
> Jim Ialeggio
> jim at grandpianosolutions.com
> (978) 425-9026
> Shirley, MA
> 
>