I don't glue my FB extension at all.
Lately I've been bolting them, either way, 4 years and no problems so far......Clinton
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| Bracing the upper bout, concern:cracks near the FB extension http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=25123 |
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| Author: | enalnitram [ Mon Dec 21, 2009 12:51 pm ] |
| Post subject: | Bracing the upper bout, concern:cracks near the FB extension |
I'm working on my second and have been planning to leave out the popsicle brace. It's a 00, 14 fret, and I'm basically copying from pics of Martins from the 30's. Has anyone here built a guitar that has developed cracks (or other problems) near the FB extension, due to light bracing? I'd like to hear some stories, if anyone has any to share. thanks! |
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| Author: | Alexandru Marian [ Mon Dec 21, 2009 1:10 pm ] |
| Post subject: | Re: Bracing the upper bout, concern:cracks near the FB extension |
Try the A-frame type. It eats only a little from the UB space but adds support against the FB crack and against string-pull-folding too. |
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| Author: | Alan Carruth [ Mon Dec 21, 2009 2:20 pm ] |
| Post subject: | Re: Bracing the upper bout, concern:cracks near the FB extension |
The A-brace won't keep the shrinkage of the f-board from pulling cracks in the top, it just helps keep the neck from shifting in once the top does crack. I make a 'chin' on the neck block that is wider than the fingerboard, and extends out almost to the UTB. So far, so good... |
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| Author: | Darryl Young [ Mon Dec 21, 2009 2:24 pm ] |
| Post subject: | Re: Bracing the upper bout, concern:cracks near the FB extension |
Mario advised me that these cracks are often caused by the difference in expansion between the fretboard extension and the top with humidity changes (low humidity often being the culprit). From Mario's recommendations, you might try glueing the fretboard extension lightly around the perimeter where the glue joint will fail before the soundboard cracks when the humidity drops. |
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| Author: | enalnitram [ Mon Dec 21, 2009 2:41 pm ] |
| Post subject: | Re: Bracing the upper bout, concern:cracks near the FB extension |
Darryl Young wrote: you might try glueing the fretboard extension lightly around the perimeter where the glue joint will fail before the soundboard cracks when the humidity drops. I like the theory and I'm a big fan of Mario. Can you explain this a little more? glue lightly where? |
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| Author: | Darryl Young [ Mon Dec 21, 2009 9:52 pm ] |
| Post subject: | Re: Bracing the upper bout, concern:cracks near the FB extension |
First let me say that I'm no Mario......so take what I say with a grain of salt. If I understood Mario's point correctly, he recommended glueing lightly around the perimeter of the fretboard extension (on the bottom of the fretboard where it glues to the soundboard). This should hold fine as long as you aren't in very low humidity conditions. In low humidity, the fretboard and soundboard both shrink.....but at different rates.......sometimes creating enough pressure to split the soundboard along the edge of the fretboard. You want the glue to fail before enough pressure is created to cause damage. This saves the soundboard, and you can always work more glue under the fretboard extension and re-clamp after the guitar is rehydrated for an easy repair. Again, I'm not an experienced guitar builder and certainly can't give advise with authority and expertise like Mario......but that is the way I understood his point. |
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| Author: | Alexandru Marian [ Tue Dec 22, 2009 3:57 am ] |
| Post subject: | Re: Bracing the upper bout, concern:cracks near the FB extension |
I guess I always pictured the A braces as covering all the FB edge, they would probably need be less slanted for that, and wider. |
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| Author: | bluescreek [ Tue Dec 22, 2009 7:21 am ] |
| Post subject: | Re: Bracing the upper bout, concern:cracks near the FB extension |
There are 2 forces acting here , the expansion and the shear . I use more of a cleat under the fretboard . It is about the size of the popsicle but only extends about 1/2 inch on either side. You need something here to help control those forces , Whether you glue light or heavy won't make a difference , if the expansion and shrinkage gets to the point of failure it will . You should use something. |
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| Author: | enalnitram [ Tue Dec 22, 2009 9:10 am ] |
| Post subject: | Re: Bracing the upper bout, concern:cracks near the FB extension |
bluescreek wrote: There are 2 forces acting here , the expansion and the shear . I use more of a cleat under the fretboard . It is about the size of the popsicle but only extends about 1/2 inch on either side. You need something here to help control those forces , Whether you glue light or heavy won't make a difference , if the expansion and shrinkage gets to the point of failure it will . You should use something. Thanks, John. After reading a lot about it yesterday I sorta came to the same conclusion. I was considering making a flat piece of spruce that was a little wider than the FB but that would butt up against the transverse brace and the neck block. I like your smaller idea. |
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| Author: | Tim L [ Tue Dec 22, 2009 10:57 am ] |
| Post subject: | Re: Bracing the upper bout, concern:cracks near the FB extension |
Quote: I was considering using a flat piece of spruce that was a little wider than the FB, but that would butt up against the transverse brace and the neck block That is what I have been doing on my last 4 guitars, which is a couple of years worth. I make the patch so that it runs from the edges of the neck block and then runs in a line that would be tangent to the soundhole, stopping at the TB. I make it just a bit thinner than the top and run the grain lines the same way. Seems to work well but I also have been thinking about either going to the small TB, as John is doing, or going back to a chin on the NB. I am trying to shed weight where I can, so the method John is using is the direction I will probably go. Tim |
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| Author: | crich [ Wed Dec 23, 2009 11:53 am ] |
| Post subject: | Re: Bracing the upper bout, concern:cracks near the FB extension |
I don't glue my FB extension at all. Lately I've been bolting them, either way, 4 years and no problems so far......Clinton
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