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Finger brace placement
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=27517		 Page 1 of 1
Author:  David Malicky [ Sat May 22, 2010 2:26 pm ]
Post subject:  Finger brace placement
I'm wondering about the placement of the finger braces relative to the bridge. Most bracing patterns I've seen have at least 1 finger brace next to the bridge / bridgeplate, and some have both fingers 'coming off' the bridge plate (X-leg in between them, of course). Some luthiers (Somogyi, Poling) seem to be pretty intentional about this. Maybe the bridge can 'drive' the fingers to some extent if they ~intersect, but maybe that would also require the fingers to be rigidly joined to the X legs (butt-joint). Or maybe it doesn't really matter, especially if the fingers taper to 0 before intersecting the X?

Has anyone run experiments on finger placement and joining methods? I ask because my current 13-fret 25.0" scale GA design (forward shifted, 98 deg) places the bridge right in between the fingers (pic below).
Author:  Brock Poling [ Sat May 22, 2010 2:43 pm ]
Post subject:  Re: Finger brace placement
I find these finger braces to be an important part of bracing the top. Depending on the size of the guitar I will either use 1 or 2 per side. GC/OM guitars are getting 2 now my my current methods. What I want is for them to be as close as possible to originating from under the bridge (and never outside of the bridge plate). I make solid contact with the X-Brace. If you look at my bracing patters I only relieve the top of the fingerbrace that is touching the x-brace and I taper them toward the edge.

I think of them more as a channel to drive energy from the bridge into that area of the top plate rather than any type of structural support. If I were bracing using your top, I would angle the finger braces in a bit more so the parts that touch the x-brace woud be in line with the top and bottom of the bridge plate. I would probably keep the outside edge about where it is.

Sorry for the weird crop, but here is an example of one of my more modern voiced instruments.
Image
Author:  Howard Klepper [ Sat May 22, 2010 3:02 pm ]
Post subject:  Re: Finger brace placement
I like the forward (or on a small guitar, only) finger braces to go under the forward corners of the bridge. I don't like the idea of that 90º (or similar) corner rotating down into the top with nothing underneath it. I also like the idea of the stress in those corners being carried forward to the side in a stiff area--just below the waist. I think of them as very important structurally, pace Brock.
Author:  Burton LeGeyt [ Sat May 22, 2010 3:17 pm ]
Post subject:  Re: Finger brace placement
I run a brace all the way across the top at the front of of the bridge (under the X). I also extend the braces that flank the soundhole into the neck block and the other way through the x upper arms to terminate at the point under the bridge wings.
Author:  woody b [ Sat May 22, 2010 3:52 pm ]
Post subject:  Re: Finger brace placement
Howard Klepper wrote:
I like the forward (or on a small guitar, only) finger braces to go under the forward corners of the bridge. I don't like the idea of that 90º (or similar) corner rotating down into the top with nothing underneath it. I also like the idea of the stress in those corners being carried forward to the side in a stiff area--just below the waist. I think of them as very important structurally, pace Brock.



Like this? [:Y:]
Author:  Brock Poling [ Sat May 22, 2010 4:56 pm ]
Post subject:  Re: Finger brace placement
Howard Klepper wrote:
I think of them as very important structurally, pace Brock.


Perhaps I should clarify. It isn't I don't think there is any structural benefit in these braces. My point was they don't have to be very heavy at all. And tonally I think they give you a big bang for your buck.
Author:  David Malicky [ Mon May 24, 2010 1:21 am ]
Post subject:  Re: Finger brace placement
Thanks, all, for the detailed replies and advice! I'm understanding the issues better, and I see I have some good options to work with. And that's an elegant top, Brock!
Thanks again, David
Author:  alan stassforth [ Wed May 26, 2010 8:00 pm ]
Post subject:  Re: Finger brace placement
hey brock, would you consider your bracing "to the edge"?
also, are you going to let the top of the x brace into the kerfed linings?
looks like i'm heading in the direction of not letting the braces in.

a
Author:  Blanchard [ Thu May 27, 2010 10:49 am ]
Post subject:  Re: Finger brace placement
I have tried lots of different shapes, sizes and positions for the finger braces and have never really found that any one configurations is, in and of itself, any better than any other.

I now use the finger braces to influence the long grain to cross grain stiffness ratio of the top . For example, if the top has less cross grain stiffness than I would like for that particular guitar, I splay them out so that they are more horizontal. The effect is subtle but when combined with small adjustments to other brace angles and variations in the way the top itself is graduated, the cumulative effect can be significant.

Mark
Author:  Brock Poling [ Thu May 27, 2010 11:30 am ]
Post subject:  Re: Finger brace placement
alan stassforth wrote:
hey brock, would you consider your bracing "to the edge"?
also, are you going to let the top of the x brace into the kerfed linings?
looks like i'm heading in the direction of not letting the braces in.

a


Do you mean to the edge of implosion? No, but it is pretty light. I have been getting better results with a slightly heavier top and lighter bracing, rather than driving the plate as thin as you can. I am deflecting to .200" as I am thinning the plate initially.

I tuck the upper legs of the X in the linings, and feather the lower legs out to nothing. None of the other legs tuck but many run right to (or just short of) the linings.
Author:  Darryl Young [ Thu May 27, 2010 9:46 pm ]
Post subject:  Re: Finger brace placement
Interesting approach Mark. Thanks for sharing that.
Author:  Haans [ Fri May 28, 2010 3:34 pm ]
Post subject:  Re: Finger brace placement
Kinda sounds like Larsons...

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