The process depends on the perpendicular-to-grain compression strength of a relatively thin spruce panel. This is variable one board to the next. It is also an long-term uncertainty. That is, it is impossible to predict how a specific piece of wood--and, by extension, a panel--will respond to variations in moisture content. Averages can serve as a guideline, but individual samples at each extreme will always respond differently to the same MC changes. No matter how carefully the construction process is controlled it simply cannot produce a consistent and predictable result. If the bridges are planed to height, notched, drilled, pinned and strung during a relatively humid period (with the board bellied up high) what happens when the next spell of cold, dry weather comes along? Or, perhaps worse, what happens if the bellying goes on when everything is relatively dry. What happens when the next humid period comes along and the board has no place to go? As you say, it is a fundamentally instable system. ddf Delwin D Fandrich Piano Design & Fabrication 6939 Foothill Court SW, Olympia, Washington 98512 USA Phone 360.515.0119 — Cell 360.388.6525 del at fandrichpiano.com — ddfandrich at gmail.com -----Original Message----- From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of John Delacour Sent: Thursday, July 14, 2011 3:42 PM To: pianotech at ptg.org Subject: Re: [pianotech] Measuring Crown Radius At 15:08 -0700 14/07/2011, Delwin D Fandrich wrote: >Unless there has been a change in process the assembly is also dried >down prior to being glued in the rim. Yes, I assumed that was the case, and that this is also crucial to the process and to the fundamental instability of a system constructed by this method. JD
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