We have found that computer numerical control (CNC), specifically of wood routers, offers a precision that is immediately apparent. It can also be used to significantly reduce the effort of rough-cutting before hand-finishing. The accuracy we need, for example when inlaying fingerboards, necessitated the in-house design and construction of a CNC router (the BEAST) with paralleled motors driving both sides of the gantry that holds the router. This CNC machine is routinely used for general woodwork projects, not just luthiery-related projects

In our luthiery endeavors we have used these machines, in particular the in-house BEAST, to make components for guitars (archtop, flat top and cigar box) and banjos: inlayed fingerboards (that include pocketed fret slots), tail-pieces, bridges, finger rests, and headstock overlays. Inlays have been of abalone and colored epoxy. We have also completed the three-dimensional drawings of arched top and back guitar plates, including top bracing, and proved their validity by CNC routing a 0.4545-scale guitar body. A full-size archtop guitar, were it to be tap-tuned, would need final plate and brace thicknessing by hand to achieve the required resonance frequencies.

There are lessons to be learned, of course, which we will try and pass on. Many concern three-dimensional machining. Of course start with inexpensive wood, and making a scaled-down version is a good idea too. We were doing exactly that for our first attempt at a guitar top plate. Full size these are around 5 mm thick, and we made one at about 0.4 scale, so it was intended to be about 2 mm thick. The picture tells what happened.

It is important to correctly specify the wood thickness! If you don’t, and you are making something thin, bad things can happen.