With the rosette completed, I need to get the top to final thickness. I want it to be a little thicker in the middle of the lower bout than around the edges, which can be left a little thinner, since the sides provide quite a bit of stiffness here. The result is like a speaker cone, which has a thick middle vibrating freely adjacent to paper thin edges. Well, the edges of the guitar top aren't paper thin, but you get the picture.
I can leave it a little thicker in the upper bout as well, since this is an area that has less of an effect on sound than the lower bout yet is subject to some stresses in that the fretboard which extends over this area is being pushed down into the soundboard.
Oh, and there's a big hole in the middle of this area. That tends to weaken things as well.
I track my progress I use a thickness gauge mounted on a plywood holder with a deep neck.
I plot the thicknesses of various areas and note which areas need a lot of work and which are almost there--and which to stay away from.
.130" is good for the middle--I'll bring it down to .125"--but too thick for the edge, as you can see at the top. I work to bring all the edges down to about .110" It's a lot of clamp, scrape, unclamp, draw the body shape, measure, and repeat, but after about an hour, I have everything where I want it. I do a quick sanding of the entire top just to clean it up.
Now it's time to cut out the soundhole. I set the top back on my workboard and use the circle-cutting jig to cut the soundhole:
On my first guitar I signed and dated the soundhole, and decided that I would do that as a keepsake for all my guitars. I rub a little oil finish on it to protect it, and it's done. Here's the soundhole for #003.
It's mounted in my workshop with the other two.
The last thing for today is to cut the top to the shape of the guitar. I do this at the bandsaw, staying just outside the pencil line. Look, Ma! It's starting to look like a guitar!
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