Friday, February 5, 2016

Installing Kerfing, Rosette and Bracing

For this sinker Redwood top I decided to go with a classic Herringbone rosette. I laid out the pattern in pencil and sealed it with a thin coat of lacquer to help prevent end-grain splitting while routing. I used the router with a sound hole cutting jig to carve a circle partially into the top. I took my time measuring my cuts, practicing on a piece of scrap wood. When I made my final passes, it worked out just as I had planned and the Herringbone was a perfect fit.
I decided to add an outer ring by inlaying purfling strips to accent the rosette, I dampened the strips and bent these by hand using a bending iron. I placed a thin bead of glue in the bottom of the channel before inlaying the rosette and ring, clamped it and let it dry. Using scrappers, I removed the excess height bringing it flush to the Redwood. I finished by sanding it out before using the router one last time to cut out my sound hole.
Next, I laid out my measurements in pencil and started work on the bracing. I took a piece of Adirondack spruce, tilted the bandsaw table to match the end grain vertically and preceded to re-saw the spruce to get the best quarter-sawn stock possible. I decided to go with a 3-ply laminate of spruce/rosewood for the upper transverse brace to provide extra strength. After cutting my braces slightly over-sized and thickness sanded them to width. I used an edge sander jig to shape a 50’ radius into the bottom of the lower braces, notched and fit the x braces together and started the gluing process using a go-bar clamping deck.
I placed a 50’ radius dish in the bottom of the deck and used strips of maple to apply clamping pressure and hold the brace firmly in place while letting the glue set. The first round of gluing installed the x brace, lower transverse and finger braces. For the second round, I flipped the dish over to give myself a flat surface and glued the upper graft and transverse brace in place. For the final round of gluing I once again used the 50’ radius dish and installed the bride plate and sound hole braces. 
While waiting for the glue to dry I took some time to install the mahogany kerfing. I have done this using clothespins with rubberbands on previous builds, but this time around I used small spring clamps. The clamping pressure was much better, and the smaller footprint allowed me to place more clamps tightly around the entire rib structure. 
Next step, shaping the braces and voicing the top. Stay tuned!
- Justin Ness