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Thinking about bridge tilt angles and apparent top thickness’
Responses
Could this be applied to repair? For instance calculating bare minimum thicknesses for a bridgeplate replacement ?
My initial response is that the modeling is more appropriate for top construction. That is, making the top structurally adequate enough to limit the bridge rotation to only 2 degrees.
Having said that, applying these calculations to repair would depend on what happened to cause failure. For example did the bridge rotate sufficiently so that the peel strength of the glue became more important than the sheer strength? In that case, either the top was braced too lightly for the string tension or strings of too high tension were used in spite of the builder’s recommendations.
So just replacing the bridge plate might well not resolve the issue. I think I need to go back to Roark’s once more and use some of the mechanical compliance models to talk more about top deformation testing. I did that a little in my book but not specifically with these models.
Cool! I take it from your string tension values (and composite top/bracing thickness) that this case is for a classical guitar? On another note, I’ve always felt that the scalloping of x bracing is an artifact of finding a way to restore sufficient compliance around the bridge after initially creating brace heights required to create sufficient stiffness elsewhere
That’s right, the values are from at least one set of classical guitar values. But I feel that the approach should work out just as well for steel string guitars as well, just a matter of putting in higher tensions and so forth. Then the compliance testing would likely need a heavier weight as well.
It’s interesting that scalloping the braces was a technique for “lightening” up certain areas of the top rather than just uniformly lowering the braces. Perhaps someone did it just to do it, and since it worked they just carried on.