Plywood shrinkage??? Laminated soundboards???

Sarah Fox sarah@gendernet.org
Fri, 13 Feb 2004 18:31:28 -0500


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Hi all,

My friend and I were examining some antique furniture, figuring out how =
we are going to restore it.  I noticed that many drawer bottoms in =
several pieces were made of thin plywood and, further, that the plywood =
panels were almost universally shrunken by perhaps 1% of their original =
size (e.g. 1/4" over a 25" span).  Moreover, the greater shrinkage =
seemed to be in width, rather than in length, with regard to the =
direction of the grain of the outer veneer.  The drawers weren't made =
this way, as the side pieces of the drawers still fit properly, and the =
bottoms have shrunken out of their channels.  Either that, or the =
original measurements were pretty sloppy, which I doubt.

How does this happen?

Perhaps repeated fluctuation in MC causes the panel to expand, compress =
against the drawer sides, and then receed, whereupon dirt and debris =
fills the void in the channel?  With each cycle, the panel is compressed =
smaller and smaller?

Or perhaps repeated MC fluctuations cause the different laminates to =
play off of each other, somehow causing longitudinal fiber =
compression???

How???

And if I'm not imagining that this is happening, what are the =
implications for laminated soundboards?  Perhaps they don't crack, but =
do they shrink?  If so, does that not present the same problem as with a =
conventional soundboard?

Just curious.  I don't have any laminated soundboard type pianos, but I =
think it's an interesting question.

Peace,
Sarah

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