Day 3: Sharp tools and a feel for the grain.

There's a knack to sharpening a chisel and indeed to knowing when it needs another touch on the sharpening stone to restore its edge. Good chisels take a good edge and hold it longer. Chuck has a neat trick for quickly honing a chisel. He makes a few passes on the sharpening stone and finishes off by holding the edge against a small buffing wheel with some polishing compound on it. It's quick and very effective.

Mass is the enemy of vibration so today's objective was to remove as much of the mass of the strengthening bars and struts as possible. In the case of the guitar back, which reflects and amplifies sound, the approach is to scallop the ends of the struts where they will meet the sides of the guitar, thus leaving the back freer to vibrate. More wood is removed by carving the struts to a parabolic cross section. This all involves a good deal of feel and individual judgement as to symmetry and aesthetics. It is finished when it looks and feels 'right'.

The process for the front is more sophisticated, since this is where the guitar's tone and timbre are generated. Front bracing patterns have been developed over the years largely on an empirical basis. Most classical guitars follow the designs developed by Antonio de Torres a nineteenth century builder who is as revered among classical guitarists as Antonio Stradavari is among violinists. Steel string guitars generally borrow from designs developed by Christian Fredrick Martin which also date back to the early nineteenth century.

The front braces and tone bars are scalloped. The idea is to leave mass in areas of the sound board where there are natural nodes or areas of little vibration and remove as much mass as possible from parts of the soundboard that are trying to vibrate. This is a trial and error approach. Chuck knows from prior art and his own experience of guitar building roughly where the nodes or dead spots are likely to be. I leave the bars high at these spots and remove wood between them. We check progress by holding the soundboard between finger and thumb and tapping it in the vicinity of the bridge plate. As wood is removed, the sound becomes clearer, more musical and sustains longer. Wood is removed and the results assessed until further removal seems to have little effect. This is called voicing the guitar.

Since the front and back of the guitar were built to curvatures of 25' and 12' respectively, the top and bottom of the sides must conform to the same curvatures to ensure a good fit and a structurally strong soundbox. The same dished pieces of MDF (medium density fiberboard) are used, this time with a sheet of coarse sandpaper in place. The edges of the sides are chalked and sanded until all the chalk is removed.

To finish off the struts, both front and back, the ends are shaved down or feathered so that they give the appearance of disappearing at the points of intersection with the sides. It's a tricky process. Fortunately I've had a good deal of carving practice by this time so the delicate work proceeds without mishap. The results are subjected to the 'paper test'. A piece of paper is slipped under the side of the guitar adjacent to the strut. Gentle pressure is applied to the side above the strut and the paper should be held firmly indicating that there is full contact between back and sides at that point.

After some sanding the three primary sound box components are completed and ready for assembly. My Marples Sheffield steel chisels were put to good use today. They have waited a long time to fulfill the purpose for which they were bought in Belfast over thirty years ago.