Making the sound board
The sound board for instruments is typically made of spruce. Spruce is used because it's strong yet very light so it transmits sound more easily.
I bought a piece of 2x8 lumber at the Home Depot for my sound board. I looked through the stack of wood until I found a piece from which a nice soundboard could be cut out, with the grain mostly perpendicular to the surface, similar to quarter sawn wood.
The first layer I cut had quite a bow to it. The kiln drying process often leaves stresses in the wood. Fortunately, the next two layers were much flatter, so I used those.
This sort of job just screams "build a jig", but I'm not planning on getting into guitar building, so I wouldn't have much use for such a jig after this build. I didn't at the time know the trick of using strings and cauls, like Pat Hawley uses , although that trick seems a bit awkward too.
Traditionally, a thickness sander is used to bring such thin material down to its final thickness, but I don't have a thickness sander, and I don't really want to build or buy one either. This method worked ok for a one-off.
But if I wanted to become a luthier, I'd definitely get a thickness sander.
For fancy guitars, with a rosette around the sound hole, both the groove for the rosette inlay and the hole itself would be cut with a router jig.
With the sound hole cut out, I used my 1:1 printout to locate where the body fits on the sound board. I made a mark 10 cm from the edge of the body on the printout, then aligned my sound board hole with that on the printout and measured back the 10 cm to place the body (see arrows in red).
The top side (facing away from the soundboard) of the ribs is typically rounded. I neglected to cut the profile into the ribs beforehand, but this had the advantage that I can leave the locations where the ribs join all square for more contact area.
Last two ribs glued on. My long reach clamps came in handy from time to time.
On checking the thickness, I adjust the fence, using a dial indicator to check how much I moved it.
I initially pushed the piece with my push sticks, but found I often slipped off the workpiece with them. Wherever I stopped even briefly, the spinning blade caused burn marks on the wood.
So I resorted to pushing it by hand. I kept most of my hand over the fence, with just my fingers extending past the fence, so that if some mishap were to occur, my hand would not get pulled down to the blade.
After gluing, I used a cabinet scraper to smooth it out and remove some of the saw marks.
I also added some flat slats between the main ribs to help hold the back together. My main concern is that the back may crack due to changes in humidity, and I figure the extra slats will make that less likely.
It was actually tempting to just make the back out of 2 or 3 mm thick plywood. The back is not critical for sound, and there's no risk of cracking with plywood. But making it out of the same wood as the sides looks much better.
See also: Pat making the sound board
Next: Assembling the body
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