Soundboard
After joining, the outside face of the soundboard needs to be smoothed, using the thickness sander and taking care to remove the minimum of material.
Draw on the outline of the guitar, using the template and aligning on the centreline. Measure from the template where the centre of the sound-hole will be and mark this on the top. A circle cutter with a small spike in the underside will allow accurate cutting of both the inside and outside diameter of the rosette channel to a depth of 1–1.5mm. The channel width is cut so that the material used for the rosette – for example, a strip of herringbone-pattern purfling – is a snug fit; otherwise glue lines will show around the edge of the rosette.
The waste between the cuts is chiselled out using a narrow chisel and a small router plane. The herringbone strip can be bent to suit, using the side-bending iron. Once a good fit has been achieved, glue is applied to the channel and the rosette pushed down into this. The top surface of the rosette should be slightly proud of the soundboard. Once the glue has dried, it is scraped/sanded flush with the soundboard.
The soundboard is trimmed on the bandsaw to 5mm outside the outline of the guitar, then thicknessed from the reverse side to the rosette. Top thicknessing is critical to the finished sound of the instrument, and will vary depending on wood used and how stiff that particular piece of wood is. Sitka spruce is normally thicknessed down to somewhere between 2.6mm and 3mm.
Cutting the sound-hole
The sound-hole can now be cut out from the rosette side using a circle cutter.
Leave a margin of about 5mm between the inner edge of the rosette and the sound-hole. The soundboard is now too thin to take the tension of the strings without collapsing, so it has to be selectively reinforced with braces. The way these are glued on
