Bracing the top and back

The next phase of construction is bracing the top and back of the guitar. Remember, the top is made from spruce, a very soft wood. The final thickness of the top is planed down to approximately 1/8". This is a very thin structure to support the tension of the strings in the completed guitar. The top must be braced with thin ribs of wood to help support the tension. The back is a little harder and more dense wood but it is also very thin, approximately 7/64", slightly thinner than the top. It also must be braced to support the ultimate tension and stress of the strings. The wood most commonly used for the bracing is spruce or red cedar similar to the wood used for the soundboard. I did not have enough spruce  left from the top to use for braces and as I mentioned before there are no local suppliers of this type wood. Matthew suggested that I use some furniture grade pine that he had. The pine was light and soft like the spruce. It was also straight grained but it did have some knots that had to be worked around. I started cutting it up into the appropriate widths and lengths while trying to cut around the knots. I cut enough for all the braces and then cut long strips that I would later use for kerfing support when I attached the top and back to the sides.

Before I finished the braces and attached them to the top and back I had to decide how I was going to clamp them on while the glue dried. I also had to figure a way to make them slightly curved to match the radius on the top and back. Although the common name for a steel string guitar is a flat top guitar, there is nothing flat about it. Most guitars have a slightly curved top. This is achieved by shaping or hollowing out the face of the solara about an 1/8' and matching that arc on the bracing. The back has an even greater arch which is achieved in a similar manner. A large number of wide throat clamps would have to be used in attaching the braces or a clamping system called a go-bar deck could also be used. Since I didn't have either I decided to make a go-bar deck. The go-bar deck is a simple device consisting of a flat base with a top attached about 24" above the deck. The top is separated by four corner posts about 24" long. Strong flexible go-bars are cut from hardwood slightly longer than the 24" space between the base and the top. These go-bars are flexed and placed between the top and the base of the deck creating even pressure down on the glued brace. This clamping system was the easiest of all the jigs to build and has been a huge help in gluing up components for the guitar.

Go-bar deck gluing up the center brace on the back.

More go-bars on the center brace.

Detail of go-bars clamping the center brace, notice the cross braces used as spacers.

I arched the back braces on the belt sander to a template I created to keep the arch consistent. I traced the template on to each brace using a center line to keep the placement uniform. I then carefully sanded to each line, trying to keep each arc smooth and uniform.

Arch template for back braces.

I also arched female forms on wider wood strips using the same arch template. I mounted these female counter forms on a flat particle board base that would be placed on the base of the go-bar deck below the back to help transfer the arc of each brace and curve the entire back.

The arched female forms aligned and attached to the back glue up board.

Closer view showing the arch and the center line.

The arched back board, the back and the braces in position to glue on the go-bar deck.

The go-bars applying pressure to the first brace.

The go-bars applying pressure to all of the braces.

A closer view of all the go-bars and braces.

One of the advantages of the go-bar system is the ability of gluing all of the braces at one time. Even with enough wide throat clamps it would be impossible to glue and clamp all the braces at one time. Generally you would glue one or possibly two braces at a time let them dry and glue the next two. In a couple of hours I am ready to  finish shaping the braces with a block plane, chisels and then sand them smooth. Even though most of this bracing won't be visible the craftsmanship is very important for the final tone quality of the instrument.

Roughly shaped braces glued in position.

Shaping the braces with a block plane.

Finishing the shape with a chisel.

Final sanding.

At this point most of the books suggested that I start tapping the back and front to check for tone quality. So, I did. It sounded like a piece of wood being tapped. Seriously, I have no reference to what the sound should be so I am going to assume it is great and move on. The next step was to basically do the same thing with the top. The brace placement for the top is quite different than the back. The top or soundboard has more impact on the tone and sound quality of the guitar and the brace placement is essential to that tone quality. All of my books and all of my plans called for a standard Martin X brace system. There were slight variations in each of the plans. I decided to go with the original plans I started with from the Internet. I cut each brace and rough shaped it with the band saw. I used my solara that I made in the beginning as the base to transfer the radius to the top. I also used the solara and the washer technique to transfer the solara arch to each brace, then carefully sanded each brace to match the arch line. I marked and glued them in position using the go-bar deck.

The go-bar deck gluing the braces to the top.

Closer view of the X pattern, notice the hole in the center of the top brace.

The neck will have an adjustable truss rod in it and a hole for access to this adjustment had to be drilled in the top brace directly above the soundhole. The adjustment nut takes a 5 mm allen wrench, so the hole had to be big enough to allow the wrench to easily go through.

5/16" hole for truss rod adjustment.

Top with all braces glued in position including the bridge support.

Close up showing the X brace and delicate support braces.

The fit for the X brace proved to be one of the more challenging aspects of this project. It is a simple lap joint. I have done this type of joint many times and thought it would be no problem. This particular X brace was not 90 degrees. This was a bigger problem than I thought but it is structurally sound and no one can see it in the finished guitar, so I'm good. The back and top turned out well and are beautiful works of art in their own right.