Vince: I may have been a little hasty in describing older soundboards as having tension at the edges and compression near the bridge. This may not alwa= ys be so. The bevel of the inner rim can cause this but there are other thi= ngs to consider. The subject of crown is complex. What I should also point = out is that if the s.b. has adequate crown the downbearing forces will be eve= nly distributed throughout the board mostly in the form of compression. This= is because the curve of the crown directs the forces in line with the soundb= oard surface. This is similar to how an arch works to support a load in architecture. In older boards with little crown the bearing forces will = not be evenly distributed throughout the surface of the board. If the bearin= g is increased during rebuilding the board may de stressed beyond what would b= e safe for a newer board. In cases where the crown is gone or even curved under, the bearing force can be acting on the board in tension, pulling i= t apart. = As I said before the main reason boards lose crown is because the panel becomes narrower across the grain. There are two causes of the narrowing= =2E One: Compression set due to wood movement. Two: creep coursed by the = time the board is under stress ( time dependent deformation). In a sense your= had it right in saying that the board has shrunk or has lost it=92s elasticit= y. Only I think these terms are imprecise and easily misunderstood. = If you think this is of interrest please post. = John Hartman
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