Many of the builders of Manouche guitars in France in the 40s, 50s and 60s used molded laminated arched backs, usually without braces, occasionally just one or two. Once the molding technique was figured out, the backs could be laid up as quickly as flat backs and the lack of braces saved time in construction. The lack of braces and the molded shape also changes the way the back vibrates, for better or worse. Not to mention it looks way cool!
Here is a pic of a Busato Gran Model with an arched “violin” shaped back.
The stiffness of these backs vary anywhere from very rigid to scary flexible. The more rigid ones don’t seem to sound much different than conventional flat backs forced into an arch or spherical shape by the braces and back, though they do afford more body volume for the same side width which reinforces the bass response. The flexible ones, however, seem to lend a distinctive sound signature to the guitar, a very fundamental sound with minimal coloration. This is what I’m interested in, so mine will start off more on the flexible side.
I’ve been thinking about this for a couple years and have always been a bit intimidated by the molding process, but once I got my head wrapped around it, it was easier than I thought. Took three hours to make the mold and a couple hours to get the vacuum bag clamping system set up.
Here are some pictures of the mold, the bagging and the first back.
I used full width mahogany for the first one and the result is excellent. Full glue dispersal, no blisters or bubbles, very uniform thickness and minimal distortion when removed from the mold. My braced backs with four veneers typically weight 270 grams, it will be interesting to see what this five veneer arched back without braces weighs when trimmed up. I can probably get it lighter by using a little less epoxy next time. I’m leaving it untrimmed for now and clamped to the mold with spring clamps to help keep the shape. Once glued to the sides, the shape should be very stable I look forward to building up a guitar with this back in August.