Soundboard Clamping for Downbearing

[Ron Nossaman]

>One thing I have never been able to clearly picture in my head (or rather, 
>one of many). If I wish to notch the bridge outside the piano, I need to 
>temporarily mount bridge to board, set board into case and set plate at 
>final resting height (on dowels or adjustable bolts, etc.). When I have 
>the plate in, how do I clamp the board down to the rim securely for 
>determining final bridge height?

Who about assuming that if the crown will hold up the string bearing after 
installation, it will hold down the board perimeter while you're setting up 
the bridge height? Pre-load the board with wedges or whatever, and do it 
like you normally would. After the board is glued in, double check bearing 
and adjust with minor plate height or aliquot bar thickness changes if 
necessary.


>At what MC do I have the board for this procedure (I would assume 
>equilibrated with room RH - maybe 9%)?

I like the board a little drier, so I'm setting "winter" condition bearing 
with not much of what I'm seeing in crown coming from the panel.


>Looking a step further, if I then dry the board down prior to installation 
>and then glue the board to the rim, can I be pretty sure the board will 
>crown right back to the test height when I measured for bridge height?

It'll be pretty close, if the MC is similar. I dry my boards back down some 
before gluing them in. They do grow beyond the ribs a tad as they swell, 
and I figure I want the panel between the ribs at the edge of the board 
under about the same compression as the panel on top of the rib. I doubt 
that it makes any real difference though, one way or another. If you fitted 
the panel in the piano dry, you're more likely to get it back in when it's 
as dry as when you fitted it. And a glue joint that isn't already failing 
as you watch won't be bothered by the drying. It will take temperatures 
high enough to damage the wood to damage the glue joints.

Which brings up a question. We have a few folks on the list here that have 
or have had a thing or two to do with the manufacturing of pianos. Can any 
of you guys tell me what glues are used in soundboard assembly by the 
manufacturers you work(ed) for?

Ron N