How to Lay Out Guitar Braces
Guitar braces strengthen acoustic flat-top guitars. They are glued to the underside of the top, or soundboard, and force it to bulge out slightly. Different guitar designs and sizes allow for variation in bracing, but most guitars have similar brace layouts. X-bracing was developed in 1915. Braces are most commonly made from strong woods, such as spruce. Tonal qualities of a guitar are altered by the size and position of braces.
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Instructions
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Turn a guitar soundboard upside down so you can mark out your brace layout on the underside. Orient the soundboard so the smaller, neck end is away from you and the bottom of the guitar's soundboard is closest. Designate the far end "north" and close end "south." Make sure the layout allows space for braces that will be 3/8 inch wide.
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Draw the first brace line across the upper bout of the guitar east-west from the widest point to the widest point. The upper bout is the smaller of the two bulges that make a guitar's distinctive shape. Use the ruler to keep your lines straight. The line should pass the sound hole on the north side.
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Mark two points at the east and west edges of the soundboard. These should be positioned halfway between the line you have just drawn and the thinnest section of the soundboard across the middle, between the two bouts. From each mark draw a diagonal line to the widest part of the soundboard in the larger bout on the opposite side. These lines should form an X-shape crossing in the larger bout to the south of the sound hole.
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Draw two parallel lines running north-south between the first line you drew and the two X-lines. These should be at right angles to the first line and pass about 1/2 inch either side of the sound hole.
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Mark two points on the X-line that runs northeast-southwest. The points should divide the length from the cross point to the soundboard edge into equal thirds. Use a protractor to measure an angle of 100 degrees from the line at each of these points and mark them. Draw a line at each point running approximately northwest, from the X-line to the edge of the soundboard, at the marked angle.
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Create a mirror image of the two lines you have just drawn. Divide the other X-line, from the crossing point to the southeast corner, into thirds. Likewise, measure and mark two angles of 100 degrees from the line, this time running northeast. Draw two new lines from the X-line to the edge of the soundboard at this angle.
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Draw two further parallel lines that run approximately from the southwest corner of the soundboard to the X-line opposite. They should split the space to the south of the cross in the larger bout into approximate thirds. The layout is now ready for the braces to be glued in place.
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Tips & Warnings
None of the lines, with the exception of the X-lines, should cross.
The bottom plate of a guitar is usually braced, too, but with a simpler pattern than the top.
Professional brace layouts, which take into account acoustical variations, are available but at a cost.
Don't damage the soundboard by pushing too hard with your pencil marks.
References
Resources
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