----- Original Message ----- From: "Phillip Ford" <fordpiano@earthlink.net> To: "Pianotech" <pianotech@ptg.org> Sent: August 17, 2003 2:46 PM Subject: Re: More on soundboard crown > > This is discouraging. Are you saying that there is no lower limit > below which there won't be compression set? In theory, yes. Though this subject has come up in the past as well and has been the recipient of some debate. On a practical level the rate of compression set at very low levels of compression can be so low as to be assumed negligible. > > If so then every > soundboard is doomed to flatten. Even on rib crowned boards the ribs > are subject to some level of compression load on their upper fibers > due to the bending loads imposed by the downbearing. Again, in theory this is true. However, both the tensile strength and the compression strength of wood taken longitudinally (parallel-to-grain) are so high relative to the rib loading that in a rib-crowned soundboard system compression set can be virtually ignored. At least this is so with a reasonably designed rib set. The problem is the relatively low perpendicular-to-grain compression strength of spruce. The compression-crowned soundboard system loads--stresses--the panel to fairly high levels in this plane. The rib-crowned soundboard system avoids stressing the wood in this plane. Del
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