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Thread: Tenor Koa top thickness?

  1. #11
    Join Date
    Mar 2017
    Location
    Arlington, WA U.S.A.
    Posts
    366

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    Sequoia,

    Thank you for the bracing photo. That raises 3 questions:
    1. What is the little block under the center brace?
    2. How thick is the bridge plate you've used?
    3. There looks to be quite a lot of space between the 3 long lower braces and the lateral one below the sound hole. My only experience is from the LMI tenor plan and they're much closer in that plan.
    "Why is it that you never have time to do it right the first time, but you always have time to do it right the second time??"

  2. #12

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    It's an unanswerable question really. Koa can vary from almost an iron wood density to a spruce density. Grain flame and curl all figure in. I look for stiff but light weight for tops. That's before we even wander into the bracing scheme. If you had a fantastic sounding instrument laying around I would tell you to take the bridge off and try to get about the same deflection. Whatever you decide to do measure the stiffness before bracing even if it's just flexing it with your hands so you can begin to develop a reference. Most new builders tend to over brace.
    Michael Smith
    Goat Rock Ukulele
    www.goatrockukulele.com

  3. #13
    Join Date
    Oct 2014
    Location
    Little River, California
    Posts
    2,333

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    Quote Originally Posted by ChuckBarnett View Post
    Sequoia,

    Thank you for the bracing photo. That raises 3 questions:
    1. What is the little block under the center brace?
    2. How thick is the bridge plate you've used?
    3. There looks to be quite a lot of space between the 3 long lower braces and the lateral one below the sound hole. My only experience is from the LMI tenor plan and they're much closer in that plan.
    1. Ah yes, my maybe silly little invention (?) which I call the "bite me" patch. The patch goes under the central fan which has been notched. The idea is to distribute the upward force on the top by the central fan as the bridge wants to rotate forward. It also distributes the pressure on that vulnerable top join between the heel block and the brace which can possibly cause splits (cracks?) down
    the line.

    brace1.jpg

    2. The bridge plate is ~0.1 inches more or less. I don't get too hung up on bridge plate thickness as long as the grain is perpendicular (90 degrees) to the grain of the top.

    3. I believe that the fan braces should NOT be tied off (butt joined) to the lower transverse brace. Strong structurally but acoustically deadening. Just my opinion. However the distance between the lower transverse brace and the fan braces is probably not that big a deal. Close but not too close.
    Last edited by sequoia; 02-17-2020 at 03:25 PM.

  4. #14
    Join Date
    Mar 2017
    Location
    Arlington, WA U.S.A.
    Posts
    366

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    Sounds like good advice, Mike. But I'm sure I'll be scratching my head as I wonder what on earth what I'm doing means. Nonetheless, I will be flexing away.
    "Why is it that you never have time to do it right the first time, but you always have time to do it right the second time??"

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