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Thread: Rebracing top on my Guild JF30

  1. Default

    Quote Originally Posted by Left of Sam View Post
    Thx mark! Ok you're too analytical for your own good (as I am ). I just cut those little pieces out to translate the bracing layout to the actual top and/or back. Easy peasy!

    I choose the tapering/scallop points visually by staring at pics of braced tops/back that are tried and true.
    You aren't the first person to have told me that! I had a friend (now deceased, sadly) who told me I should stop thinking so much, I wasn't very good at it. But, in my defense, now I know why the holes are in the blueprint, AND how you determine where to start your tapering/scallop points

  2. #22
    Join Date
    Jan 2013
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    Bend, Oregon
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    Haha I'm right there with you and there's really not anything wrong with being ultra-analytical! So we gotta be we hehe

    Ok, basically final bracing of top and back. Glueing back on right now!

    Jf30 by Sam Van, on Flickr

    Jf30 by Sam Van, on Flickr
    Last edited by Sam Van; 09-20-2016 at 01:43 AM.

  3. #23
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    Jan 2013
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    Bend, Oregon
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    Ok i glued back on a bit crooked and we just won't be tolerating that! Also when tapping body, the resonant frequencies of top vs back were good but the top had no sustained resonance.

    So I looked deeper into the bracing of j-200s and determined my X was a little too tall. I was also comparing the heights to the original bracing of this jf and those were pretty tall. But actually if you look at the original braces, there's a lot of grain lines showing in them which means they are not very quartered. My new braces are close to perfectly quartered with very little runout. As well, the Young's modulus (stiffness) if this exact wood is quite stiff. Thus, going a bit lighter is likely aok.

    So here's a pic of the "final" brace shapes, 16 mm at the X, which is pretty standard for jumbos.

    Also note that I filled the center seam separation with a sliver of spruce.

    Jf30 by Sam Van, on Flickr

    1940 sj-200 for comparison:

    Last edited by Sam Van; 09-20-2016 at 02:13 PM.

  4. #24
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    May 2006
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    Leesburg, GA
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    Sam,

    Good golly, miss molly, this is awesome! I just saw this thread today and I'm spellbound. I would love to do this one day... just gotta make "one day" sooner instead of later!

    Can't wait to see the final product!

    Gary

  5. #25

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    a fascinating look "under the hood"

  6. #26
    Join Date
    Jan 2013
    Location
    Bend, Oregon
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    Ok back is (re-attached)! Body chamber is resonant but not boomy. I could actually put bridge on and string it up but I think I'll wait to finish the back.

    But now the hard part. Putting on a new back binding. The old one is crusty. As well, the new back is not nearly as thick as the old back so the present binding channel is about half as deep into sides as before. Ill either rout deeper channel or trim binding height.

    Jf30 by Sam Van, on Flickr

  7. #27

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    Good Stuff!

  8. #28

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    Quote Originally Posted by Left of Sam View Post

    Jf30 by Sam Van, on Flickr

    Are these the final finished braces? That bottom one looks monstrous. Neat project.

  9. #29
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    Jan 2013
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    Bend, Oregon
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    Quote Originally Posted by George View Post
    Are these the final finished braces? That bottom one looks monstrous. Neat project.
    Good eyes George. I left that one a bit taller than standard because I thought the back, being so wide, might have trouble having a main resonance peak higher than the top. I think if the guild guys who originally designed this model with the curved laminated back would say they did so for his purpose. So, I wanted to keep a little stiffer back than the braces on an AJ, for example. I measured the top, back and main air this morning and indeed that back has s pretty low resonant frequency. We will see how she sounds soon enough!

    And if I think it's a problem I can always shave it down.....


    But here's a pic it's 1940 sj-200. Those are quite low......ahhhh wish I could hear or play some holy grail sj-200 to know what I want.


    Sam

    Last edited by Sam Van; 09-22-2016 at 08:07 PM.

  10. #30
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    Jan 2013
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    Bend, Oregon
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    Ok routed new binding channel, fixed little issues in top, etc

    I routed into heel of neck so I took off heel cap and decided I'll trim it down and add a new "custom" heel cap.

    Jf30 by Sam Van, on Flickr
    Jf30 by Sam Van, on Flickr
    Jf30 by Sam Van, on Flickr
    Jf30 by Sam Van, on Flickr

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