While the back was drying I had one final task to do on the top. The upward pull on the neck by the strings pushes the part of the fretboard that is glued to the top downward. Sometimes cracks can develop on the top at the edges of the fretboard due to this downward pressure. To counteract this Martin has always used a wide, thin brace that ran across the upper bout parallel to the transverse brace. I ran across a website by a luthier and guitar repairman where he showed numerous Martins that still developed cracks in spite of what he calls this popsicle brace. He instead uses a smaller trapezoidal-shaped brace that runs from the heel block to the transverse brace, with it's grain running sideways and perpendicular to the grain of the top. It's wider than the fret board and covers the entire area of the top affected by the fretboard extension, unlike the popsicle brace. A long narrow piece of wood is weaker than a short wide piece, so this makes sense, and I've incorporated it into my bracing pattern.
I didn't glue this piece on with the rest of the top braces because I wanted to wait until the heel block was in place so that I could get a precise measurement. Here's a picture of the brace in place.
I let that dry overnight along with the back. Tuesday evening I unclamped the back; we're halfway to a box!
The trapezoid brace had to be trimmed a bit to avoid the kerfing on the cutaway, and then we were ready to glue on the top. Well, almost.
It's a tradition for the luthier to sign and date the top before assembly. In an ideal world this signature would never be seen because it would entail the destruction of the instrument. It's just kinda cool, you know?
I lined up the centerline at the heel and butt, and did a dry run. I used a thin plywood caul cut in the shape of the dreadnought cutaway I did last year, and though the OM is a little smaller, with a little shifting it works. I want to use the caul because the spruce is softer than the zebrawood, and even with the tips on the fiberglass go-bars, I didn't want to take a risk of dinging it. Plus, if I had to use the bamboo go-bars I didn't want to trust the small pieces of spruce I used as cauls on the back.
The dry run showed me how many go-bars I needed and where I needed extra pressure. I undid everything, spread glue on the kerfing, end and heel blocks, and clamped it all down.
This morning I unclamped it and took it out of the mold, and now we have something that looks like a guitar! There's one more thing to do, and that's to remove the spreaders that were left inside. Even though I measure the blocks to make sure they fit through the sound hole, it's a bit of a tense time. If for some reason the wingnuts lock on the threads and won't move, well, Houston, we have a problem. I guess the only thing to do would be to heat the top or back to loosen the glue and remove it, and then work on the spreader, but I don't want to ever find out the best way to fix that problem. It's a big relief when both of the spreaders are out of the box.
And here it is.
Next up is to rout the edges flush to the sides. After a rough sanding of the sides then I'll start working on the bindings.
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