OM Style Bracing Question

[Steve Gonwa]

In the OM plans I have ( from LMI ), the two lower braces for the back plate are shown as 3/4" wide by 1/4" in height. In the plans, they appear to be a flat piece of bracing across the width of the back plate. Is it likely that these braces also have to have their bottoms radiused like the top two braces ? If I do that in my 16' radius dish, it would leave the ends of these two braces quite tapered or thin at the ends ( given that they are only 1/4 inch high to start with. ) Am I correct to radius these flat braces ?

[Clay Schaeffer]

I use the wide flat braces on the back'slower bout and also radius them. They do wind up fairly thin on the ends. I believe the added flexibility helps the back react to humidity changes without cracking.

[Steve Gonwa]

Thank you for the reply and insight.

Steve

[Mark Swanson]

Others brace the back with all of the braces thin and high, like the first two in your plan. If you look at other plans you'll see it done that way too.

[Dave Gentner]

All four of the back braces on my OMs are 1/4" wide. The upper two are about .550" tall, and the lower two are .700" tall. Works great for me.

[Bill Hicklin]

Martin makes the two lower back braces low and wide, but many builders argue with apparent logic that the girder-strength of the brace is primarily a function of height, and so tall/thin braces are more efficient for the weight. To be honest, I've done it both ways and never noticed a difference.

[Clay Schaeffer]

Hi Steve,
You will find there is almost always more than one way to skin a cat when it comes to building a guitar. Some people use wide, flat unradiused braces in the lower bout, some use tall thin braces. I use wide flat braces sanded to a 25 ft. radius. To keep the ends a little thicker (since you are using a 16 ft radius on the back) you could sand the brace to a flatter radius and "spring" it in to the 16 ft. radius when you glue it on.
There are many ways to do the back braces and if done at the proper humidity conditions, many methods will work fine.
The design of the back braces can also be used to help "tune" the back.
We picks our poison and takes our chances. <g>

[Alan Carruth]

I've been using 'ladder' bracing on the backs for a few years now, after messing with various X-brace schemes for a long time. I found that in ''tuning' them I was ending up with the bottom two braces pretty low, and didn't like the look of them, so recently I've been making them low and wide, with the upper two tall and narrow. There does seem to be a reason behind tradition sometimes!

Alan Carruth / Luthier