At 18:29 -0500 18/1/08, Farrell wrote: >I think this goes back to traditional engineering arch theory. If >you dry the board down, it will have a slightly smaller footprint >--'Course, none of this actually works - the ribs won't shrink much, >the panel top edge will just crush when it expands the 1/10 mm that >it might move and the rim has enough flex to negate any "arch" >support. There's drying down and drying down. The methods used by certain makers result all too often in compression marks that can appear even before delivery to the showrooms. On the other hand it seems certain that many makers, Bechstein being one of them at least for a long time) fitted the soundboard with too high a moisture content so that sooner or later in places with dry central heating great cracks opened up. And certain makers (I'm talking here of pre-1910) hit upon just the right moisure content for installation so that cracks in their soundboards are very rare and always due to excessive baking over a long period. I'd guess that if, as in the case of Stéphane's Ciresa board, the board was made to settle with crown at 42% humidity and the board is fitted in the same conditions, then there is very little risk of cracks appearing, wherever it is sent. As to compression marks, that's mainly a Steinway/Grotrian speciality, and Steinway at least work differently from most. At Grotrian and many other factories the board is attached to the inner rim before the outer rim is affixed -- not very practical for the restorer but very sensible, in my opinion, for the maker of new pianos. JD
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