Cutting and fitting the top braces

Unlike flat top guitars of every kind, the backs of archtops are unbraced. Even though they're only 1/8" to 3/16" thick, their curve gives them a lot of strength. The top plates are strong, too, but the pressure of 6 steel strings means they need to be braced to keep from deforming. The bracing pattern I chose - parallel bracing - puts a substantial longitudinal brace on either side of the bridge, right under the pin supports. Both braces run the length of the top, ranging from about 1/2" thick under the bridge to about 1/8" at the ends.

Because these braces are so robust, the tops can be carved thinner, which makes a brighter, louder tone on the finished instrument.

I decided to make and add the braces before I cut the f-holes, disregarding Benedetto's instructions, for no good reason except that I just thought it might be better to have the top more rigid (with the braces glued in) when I cut through the top plates, which frankly scares the shit out of me.

These braces need to fit as perfectly as possible to the tops. 

Why I have a wood room: I found a perfectly quarter-sawn, dense cedar clapboard I had put away decades ago, which I planed to 5/16 for the braces. Couldn't have bought a better piece of wood, anywhere.

Rough, bandsawn braces, after scribing to fit. Gaps of about 1/32" on all of them, in several places. NFG yet.

Remember carbon paper? I think this package is from the early '70s. I cut strips to fit under each brace, one at a time, carbon side up, "hinged" with blue tape si it can be folded back, and rubbed the brace back and forth with tiny strokes, to show high spots (where the carbon paper meets the wood).

High spots. Next, light sanding on each dark spot with a sanding stick glued up with 80 grit paper. Repeat the process until the whole stick is basically in contact with the carbon paper.

Perfect fit! As I get closer to done on each fit, I shine a bright light looking for seepage under the stick none here, with no pressure on the brace - I'm done with fitting this one.

Oops! Good fit everywhere but the last 3/4", where I must have cut or sanded too deeply. I can fix this, though.

Where the end of that one brace was cut too deep, I added a little wood, then trimmed it to fit.

Nice fit. Next, trimming them all flat to 1/8" thick at the ends, then gluing them in. 

Homemade, zero-cost luthier's clamps. I had some 7/8" cypress left over from an outdoor project. I designed and made these clamps, and glued cork to the faces. Different length 1/4" carriage bolts ( I have a small bucket of them) let them expand to whatever size I need.

New clamps in action. I outlined he gluing area with blue tape, for a cleaner job and less question about exactly where the parts go. Scraping the glue when it's wet makes an easier, cleaner job in the end.

Final planing and chamfering the ends. I've had that cheap spokeshave since I was a child.  As an adult, I've improved it and reworked it several times, and I can't imagine wanting a "better" one.