The humidity in the basement is sitting steadily at about 40%, which is fantastic for gluing braces, so I took the opportunity and braced the soundboard and back yesterday.
The plans I am using as a basis for this guitar are fantastic, however, they are missing one crucial element: the heights of the braces. The brace locations themselves are clear, if possibly inaccurate (the plans include this disclaimer, saying that brace locations were determined with an X-ray, and therefore could be slightly off). For the first Baroque guitar I built with these plans, I presented the question of brace height to Michael Schreiner, a respected early instrument builder from Toronto. From other plans he suggested that the braces could have been about 25 mm high. The braces in the first guitar are about 25 mm high, with tapered ends.
This time around, I figured I would do similarly. Then I went looking for brace wood. And I read part of a lute building book (Historical Lute Construction by Robert Lundberg). Lutes are traditionally braced with grain running parallel to the soundboard, opposite to the perpendicular grain used in modern classical guitar construction. Lundberg suggests that part of the reason for this grain direction is that most of the brace wood would have been salvaged from cut-offs from the soundboard. This seemed to be a very economical method of obtaining brace wood, so I took a look at my leftover soundboard wood. It is beautifully quarter-sawn with perfectly tight, straight grain. Using the (perhaps misguided, I will admit) logic that guitar construction was not yet standardized by any means, and that guitar construction was likely influenced by lute builders of the time, I chose to brace this guitar with grain running parallel to the soundboard. (below you can see a rather poor diagram of the two choices of grain direction, as created by me and Paint)
The Stradivarius Baroque guitar is actually fairly strongly braced when compared with some other guitars from the period. There are 3 cross struts on both the top and the back, all about 5 mm thick and of questionable height, as discussed before. These cross struts run across the upper bout, waist, and lower bout on both plates.
I chose to use as much leftover soundboard wood as possible for the braces. I managed to salvage enough wood for three braces from the cedar for this guitar. The remaining three braces I cut from another piece of cedar, from my first classical guitar. To prepare the braces I marked and cut out the braces with a coping saw, and cleaned up the faces and thinned them to 5 mm. I then trued one edge (the gluing edge) with a sanding board. All except the soundboard upper bout brace were slightly arched for strength. Although this was not necessarily a practise at the time, it does increase the strength of the instrument. The arch is subtle, so I feel that the sacrifice of tradition for strength and longevity is acceptable at this early stage in my development as a luthier.
I then glued the braces one at a time in place, respecting the center marks I had previously made on the plates. I clamped the braces with a combination of cam-clamps and medium sized spring clamps (see below).
Once dry, the braces are chiselled to height, tapered, and sanded smooth. A more careful and intelligent woodworker would probably choose to use a block plane to achieve an even height on all braces, however, I am not that woodworker. I love a good chisel, so I chiselled all of my braces to about 20 mm high, then sanded them flat. Then I used the same Japanese chisel to taper the ends (from about 2 – 2 1/2 inches away from the ends). Then I chiselled away the corners along the length of the braces. I finished by sanding them with 220 grit sandpaper.
The soundboard also is reinforced in a few places with small pads of soundboard wood. Three pads are located around the soundhole for strength, and another two located asymmetrically on the belly of the guitar. I cut these out of soundboard scraps, sanded the glue side flat on a sanding board, and glued them to in place. Once glued, they needed thicknessing to about 2mm (again, I used a chisel here, perhaps not the most appropriate tool), and shaping. Basic principle of shaping braces and pads: sharp corners are frowned upon, generally.
Before completing the soundboard, I carefully glued the rose in place.
The back required a little less work than the top, as seems to always be the case. After the braces were sanded smooth, I merely had to glue strips of paper along all of the seams from piecing the back together.
And with that, the top and back plates are braced and ready to go!