Filippo Morelli wrote:
Michael,
Good point.
To this end, I looked at a 1940's 0-15 Martin last night, in for repair at Greenridge. When we started taking measurements and inspection, it was clear that there was compromise in the dome behind the bridge. It was not a bridge/belly problem. When checking the dome, it was high but acceptable from center to edge. What was interesting ... as you moved the straight edge from heel block to bridge, the dome was asymmetrical to the base side. The treble side was dead flat. So bracing seem to have "let go", even though they were affixed.
Material stress is inevitable. Ultimately we are distributing the stress. But to that end, I would also point out that we build guitars like we build unibody construction automobiles. This is cost effective in manufacturing. Race cars are not built that way, on the other hand. One could build a frame with a sound box around it, but that's not how we build guitars. The net result would be a very different stress distribution. The counterpoint being - it's not the stress that string tension brings that is the issue. It is the stress it brings in respect to the structure that is being asked to deal with the stress.
Filippo
Filippo,
I've seen that on many old steel-string guitars, especially Martins, presumably due to the asymmetry in the the tone bar placement. Since the tone bars generally run close to the bridge plate on the treble side, and run diagonally toward the bass side, there is "loose" area of the top on the bass side that deforms more readily. We're talking bracing for right-handers, anyway. Ladder-braced guitars with symmetrical bracing seem to dome more symmetrically.
I'd agree that eventually, pretty much all conventionally built, non overbuilt guitars will need a reset. Old instruments I've seen that didn't need one yet show evidence that they're on their way to needing one someday.
Pat
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