Shaping Tone Braces

Shaping the braces for the soundboard is one of the most important tasks in impacting the tone, balance and volume of an acoustic instrument. It is critical that these braces are glued properly, with just the right amount of glue, and the excess glue is properly cleaned from the soundboard and braces surfaces. Also changing the position of the braces can drastically impact the tone production of the top. For instance by simply shifting the braces forward about 1/2″ (12mm) you can create a completely different sounding instrument.
Tools & Materials:

Wood Chisel Set
Violin Finger Planes
Lie-Nielsen Low Angle Block Plane
Flat Sanding Stick
Curved Sanding Stick
Adhesive Sandpaper 220 Grit

There are a couple of different approaches to gluing bracing to the soundboard. Some luthiers’ glue the braces in an unfinished state as simple rectangular pieces of wood that are only finished shaped on the gluing surface, and some shape braces and leave only the final sanding to the post-gluing process. I lean toward the former and will explain that method here.

No matter which method is used, be sure to cut and finish all of the braces to the correct width. The bottoms of all braces should be carefully shaped and sanded. The gluing surface is to be perfectly perpendicular to the brace sides and do not have any humps or bumps or other inconsistencies to the gluing surfaces.

Brace Arch:

I recommend that there be an arch placed on the guitar back. Reasons for this vary, but you can review this in the article on Shaping Tone Bracing for a complete explanation. Furthermore, I recommend that the top plate, or soundboard be perfectly flat, with straight top bracing. Again opinions on this vary and there are good reasons for utilizing each method. I feel that a top plate with no arch is more free to vibrate than one with an arch. Of coarse when you factor in the stress introduced with the strings, this total blasts that theory.

Let me just say that I have built guitars with both flat and arched tops. In my humble opinion, with the guitars that I built, I preferred the sound and volume of the flat-topped guitars to those I built with an arched top. As a side note…If a soundboard is constructed with a dead level top, buy the time string tension is applied, the top will actually arch up approximately 2 or 3mm, or 3/32″ to 1/8″ at the bridge, therefore, the guitar actually will have an arched top.

Braces Glued In Unfinished State:

What this means is that the braces are glued in place without their final shaping being complete. No scalloping is usually completed and the brace consists of a rectangular piece of wood that has finished sides and a finished gluing surface. I do recommend that you trace the outline of the brace shape on the sides of the braces as a rough guide during the shaping process.

Rough Shaping:

Once glued in place and glue squeeze-out cleanup, it is time to shape the braces. The best way to hog a lot of wood off the brace at the scalloped areas is with a very sharp chisel, or a small plane. Cut to within about 1mm of your line and stop.

Final Shaping:

To shape the top and sides, use a very small hand plane or better yet, get a small finger plane that is used by violin makers. These are very sharp, have very good steel and cut very quickly. If you plan to put a parabolic shape to your braces (this means the sides are rounded and blend into a much smaller radius at the top), Then a very small hand plane will be your best bet. I have a small Block Plate that is about 1″ wide and 2″ long that is invaluable for cutting the parabolic shape I prefer for my braces. I also use this plane for initial scalloping at the ends, where If finish planing with curved sole finger plates.

Final Sanding:

Once all the braces are rough-cut, take a sanding stick with 120 grit garnet sandpaper and smooth the brace to its’ final contour. Sight down the braces you make sure your a getting nice straight lines. The length of your sanding stick should be about 6″, which will help you keep everything straight. Also check to make sure the braces are not lop-sided and look balanced on both sides. Key to this is using a small, long sanding stick about 1/4″ thick x 1″ x 12″ long and using long even strokes, which will give a very consistent line on the brace.

The image gallery below shows shaping of back braces, but the same principles apply to shaping the braces on the soundboard.

  • Placing The Parabolic Shape On The Brace With a Small Block PlanePlacing The Parabolic Shape On The Brace With a Small Block Plane
  • Finishing Up The Brace With a Small Block PlaneFinishing Up The Brace With a Small Block Plane
  • Rough Sanding Brace Length With Sanding Stick Using Long Even StrokesRough Sanding Brace Length With Sanding Stick Using Long Even Strokes
  • Rough Sanding Scalloped Brace Ends With a Curved Sanding StickRough Sanding Scalloped Brace Ends With a Curved Sanding Stick
Cutting the Scalloping:

To make the final cuts for scalloping, it is best to use a violin finger plane with a convex base. This plane is designed to cut out arched violin tops so it is an excellent tool for this purpose too. Do your final shaping with a curved sanding stick, using a rocking motion to sand the scallops smooth and consistent.

Finish Sanding:

Finish sand the braces with 220 grit garnet sandpaper, until they are silky smooth. Also sand the top or back, reinforcement strips etc. until smooth.

GLS Tip #1: Finish the entire surface of the interior of your guitar by finish sanding with 400 grit sand paper and finish up with #000 or #0000 steel wool. Give this treatment to the sides and blocks, linings, top plate and braces, back plate and braces and to all the neck components within the interior of the guitar.

Concerned buyers, who know a bit about guitar construction will be impressed by the way the braces and the interior of the guitar are not only displayed, but how smooth you made the interior of your guitar.

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