Scott's Guitar Blog: September 8, 2012

Bending Sides for a Custom-Made Koa Guitar

One of the most magical elements in the art of luthiery, is bending wood into guitar sides. You are taking something thin and fragile, that is very stiff, and bending it into a series of curves, in order to become a guitar. It is literally defying common sense that this is even possible, yet it is. I use a side bending device that features 3 150 watt light bulbs, a cider-press style screw and crank, interchangeable forms, and stainless-steel sheets. The wood is cut to size and shape, made as thin as possible, then preparation for bending begins.

My father is a steel sculptor, and a few years ago I asked him to weld up a stainless steel trough that would span across 2 burners on a stove-top. It is filled with about 1/2″ of water, then heated to just under the boiling point. While this is happening, the bending machine is being prepared by cranking the steel sheets over the form with the 3 lights on. The metal gets very hot to the touch, which is important. This preheating of the machine’s steel sheets is critical for a successful side-bending.

Just as the machine reaches its temperature, the wood is placed in the hot water for a minute or so, until it is completely hot and wet. I then quickly wrap it in alumimum foil to retain the heat and moisture. It is then slid between the 2 steel sheets, and the machine is cranked down, forming the waist of the guitar. Sliding shoes are attached to springs, which are quickly and cleanly pulled along the form, forcing the steel into the shape of the form itself. This then “cooks” for about 5 minutes. I then turn off the light bulbs, let it cool for about 15 minutes, unhook the springs, and unscrew the waist-block, releasing the tension on the steel sheets. The bent wood is removed from the machine, and while still warm and slightly pliable, it is placed into a mold to dry completely. You can see in the final photo, that the wood has taken the shape of a guitar perfectly. The small gap visible in the mold at the bottom of the sides, is to be filled with an ornamental Koa and fancy marquetry end-strip.

I used to only wet the wood slightly, but I’ve found this system gives me a slightly longer working time, and gives flawless results. I learned about the heated trough in Honolulu when visiting friends who make ukuleles. They were able to work quickly, without ever damaging the wood, as it becomes very flexible with this technique. There you have it, defying nature by bending something that should really shatter into pieces when bent…into a guitar.

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