Day 11: Laminating a rib, thinning and reinforcing the soundboard, cutting struts
We began the day by laminating the second rib with two layers of cherry. It reminded me of the importance of doing a dry run of jobs like this so that all the components are in place (e.g. grease proof paper taped to the jig) and the clamps are to hand. Once the rib was clamped up, the focus for the rest of the day was the soundboard.
To begin with, I marked the outline of the plantilla and the position of the 12th fret, 107mm from the edge of the sound hole. I then roughly cut out the shape of the plantilla on the bandsaw and worked on thinning the soundboard by planing, scraping and sanding. I made sure the area that would be glued to the heel of the neck was consistently 2.5mm across and the thickness of the upper bout was also consistent (again, 2.5mm).
We used the dial gauge for the upper bout and then switched to the ‘Magic Probe‘ for measuring the thickness of the lower bout. The process was to measure, pencil the thickness at different points (e.g. ’17’ = 1.7mm) and then sand using 100 grade paper; then measure again, pencil the new thickness across the lower bout and then sand again. Each round of sanding would take off about 0.1-0.2mm. You can see in the photo that as we get nearer to the rosette, the thickness increases to over 2mm. The aim was to achieve a maximum of 1.5mm across the lower bout and especially around the bridge area. 1.5mm at this stage allows a further 0.1-0.2mm to be taken off the front when finishing the soundboard. The final round of sanding on the back of the soundboard was with 180 grade Garnet paper. The lowest reading today was 1.35mm.
The next job was to cut and reinforce the soundhole so the glue could dry over lunch. After lunch, I trimmed the soundboard with a scalpel at the position of the 12th fret (see illustration 19-3 in Roy’s book) and marked the centre line of the guitar. From there, I marked out the bridge, the lattice struts and the area of the lining.
I then bolted the soundboard to the solera and took the opportunity to mark the heel of the neck where the soundboard will fit into a recess.
The last job of the day was to shape the 18 struts for the lattice. They had been planed to 2.5mm thickness and needed to be cut to length and marked to account for the dome of the plantilla.
Each pencil line of the lattice was either given a letter (A, B, C, etc.) or a number (1, 2, 3, etc.), with letters perpendicular to numbers. Then, each strut was cut to the length of a lattice line and labeled with the corresponding letter or number. To trace the dome of the plantilla, I pressed the soundboard down while running a pencil horizontally across the strut which rested lightly on the soundboard. I then planed and sanded down to the line, checked the fit and sanded again if necessary.