Saturday, August 16, 2008

Classic guitar soundboard arching

I have a beginners question regarding the arching of the classical soundboard as detailed in your book. The soundboard appears to be arched across the lower bout because of the arching of the lower cross strut, but there is no arching of the soundboard along the centre line from the lower end to sound hole.
I also read Roy Courtnall's book, "Making Master Guitars" where the solera is domed inward across the lower bout and along the centre line from the bottom of the lower bout up to the soundhole implying an arch across and along the soundboard.
The workboard shim you describe has a narrow section of cork all around the edge of the lower bout to accommodate and hold the arched soundboard but because the shim has cork at the bottom end of the lower bout, it implies to me that the doming is both across and down the soundboard in your method. The shim doesn't appear to be used in the soundboard arching process but is used later in the assembly process. Have I missed something important in the process? Is the soundboard arched across the lower bout only or across and along the centreline of the lower bout?


The raised lip of the workboard shim simply raises the guitar off the flat workboard to clear the portion of the soundboard that has been arched by the lower transversal face brace. We don't want the brace to be squashed when the back is roped on. The more traditional solera is dished for the same purpose. You cannot assume or accept the "implication" that the workboard or the solera have anything to do with actually shaping the soundboard. How could it?

Having said that, I acknowledge two "schools" of thought here. One school affirms that the guitar is improved in some undetermined way by imparting a dome into the soundboard--by clamping the fan braces against the domed solera while they are being glued to the soundboard--and then curving the base of the bridge (requiring a bridge gluing-block to be arched to match). This would extend the size and extent of the dome, than doing otherwise.

The other school of thought--the one I favor--calls for simply arching the lower transverse brace and then gluing all the fan braces flat and not arching the bridge's down-face. We believe that the string's tension is going to eventually drag all those elastic elements into a final configuration of its' own. The first school, I suppose, would affirm that purposely doming the top would impart greater stiffness and resistance to the soundboard. But to the extent that the same result could not be achieved by simply increasing the cross-section of those top elements, they don't ascribe any other distinct advantage to the greater complication.

So I go with the simpler solution. And besides, great guitars can be achieved using either method. So why choose the more complicated option?