Back Bracing Question

[Bob Moore]

I got the bracing set from LMI the other day. I was expecting the back braces to be kind of fat and tall. It turns out the 2 lower bout braces that they put in the set are 1/4" tall and 3/4" wide. The two upper braces are very similar to what you'd use for the X braces on the top.
My question is how do I get a 15' radius on the back using those braces. I also bought a 1"x2"x23 1/2" piece of Sitka Spruce in the event I want to make my own for the back.
Below is the whole set of braces. The ones I'm talking about are on the far right side.




How would you go with this? What dimensions would you use for each of the four back braces?

Thanks,
Bob

[ken cierp]

I've seen to many of the low profile braces flatten out and loose their contour. I've settled in on 5/16" x 5/8" + --- most of the Gibson's are 1/4" x 5/8+

Of course an accurate 15' to 20' (I prefer 15') radius is very important for the back plate. One could question the acoustic properties, but unlike the top wherre the strings are pulling the plate into a dome the back needs to have a nicely shaped contour to prevent crushing the back inward -- this is where the arch principle comes into play.

[Scott Millbern]

I have recently been researching the same thing. I read about using a jig to bend the brace to the correct curve, then plane it and when released is should be planed in the correct radius.

I am building my first ground up guitar with a luthier in the city and used a ships plane. I found one used for a good price and plan to try that on my home build as well. I am not certain yet how precise I can get with the radius...

[peter havriluk]

I dealt with the same question by employing an 'x' brace centered in the lower bout and two conventional lateral braces above them in the upper bout. I used the X brace in the lower bout plus two lateral finger braces emanating from the center at right angles to the center. I wound up with a star pattern.