Official Luthiers Forum!

Is 0.110" too thin for an OM spruce top?

Depends on the strength of a particular piece of spruce ,of course.

I routinely thickness mine to .090.(as many old guitars I have examined have been.)

What type of spruce .110 is probably fine. If it is Red spruce you can probably go a little lower

r

Thanks Brad. That makes me feel better. I have read lately about people that start @ 0.120" and I got a sinking feeling. I realize that many folks use deflection testing. On the other hand, I've read that some folks believe that deflection testing is not necessary...

On an earlier build (I'm working on #5) it seems that it has some compression. Maybe the top on that one was too thin...? I'm sure that the bracing also has a bearing on this. I guess this is what experience gives you... learning not to over brace or not to under brace. ...and determining the optimum thickness of the top.

Without deflection testing, is there a good method for determining when to stop thinning the top? ...Tapping? ..."holding it by the edges and "flapping it" (for lack of a better term)?

Steve, building lots of guitars will give you that experience you describe.
Eventually your fingertips will tell you what you need to know.
Keep this in mind--that tighter waist on the OM lends strength to the whole box. You can get away with thinner tops on those smaller shapes, and providing your top isn't of the floppy variety, .110 sounds fine. I usually stop thicknessing at .105, then sand the perimeter pretty heavily.

Steve

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