Acoustic Guitar Construction

I've "standardized" my doming -- a 30' radius dish for the tops and a 12' dish for backs. I don't flatten the upper bout or otherwise adjust the top (or back) in any way. With that arrangement the geometry comes out OK with a 90 degree angle between the heel face and the top of the neck (before attaching the fretboard). Small wedges or shims (ala Taylor) can compensate for any needed adjustment.

Before any shaping or carving on the neck, I drill the end of the heel, glue in a ⅝" dowel, and install a threaded brass insert for the single ¼ x 20 screw that I'll use for attachment to the guitar body. I recess the insert about ⅛" from the face of the heel so that I can then lay the assembly on the band saw table and cut the final face of the heel using the sliding fence. Once I've made that cut, I can start shaping the neck profile on the bandsaw.

Depending on how high I set the fretboard above the soundboard, the neck shaft extension that supports the fretboard above the soundboard may want contouring to maintain an attractive spacing from the soundboard as viewed when playing the guitar. Fortunately, that can be done just before finishing, as it has no interaction with the structural geometry.

This approach impacts several structural aspects of the guitar: soundboard strength is less critical, the soundboard now having only two structural purposes: to keep the sides from deforming and to terminate the strings below the bridge -- it no longer directly prevents the neck from rotating. To prevent the neck from rotating, the torque on the neck (defined by the pull of the strings times the lever arm from the top of the headblock to the strings) now must be resisted by bracing the headblock to the sides. At the top of the sides, the upper bout wants to spread and the waist it wants to contract. (At the bottom of the sides, it's the opposite.) The top and its bracing, and the back and its bracing, need to resist that. On the top, conventional X-bracing, along with small diagonal braces from the top of the X to the headblock, work well - and aren't required to be as sturdy as is needed when the fretboard is pressing down on the soundboard. For the back, conventional back bracing is fine. To terminate the strings, the top still needs to prevent bridge rotation, so the X-brace, running below the ends of the bridge and glued to the bridgeplate, remains useful.

Bottom line, construction with the elevated fretboard is not dramatically different than with conventional designs though the X can be more delicate -- and the UTB is gone. And both of those changes free the soundboard.

A well-written explanation, thanks much. I can visualize it much easier now!

Thanks Hans, I love the following detail

... It's not that hard -- the critical issue is to get the sides of the neck heel truly straight and parallel. I build the neck first and then use the heel as a template when gluing the sides to the headblock. (Cellophane packing tape on the heel temporarily provides a glue-proof surface as well as a small clearance.) I've been surprised at how well it all works. Easy, peasy.

I have been wanting to build an adjustable neck and that requires that the heel inlet into the sides. I can use your technique to build a clean joint from the start instead of cutting one later. I feel I missed that idea as I use that technique for the end graft now. I glue it to the block before I glue on the sides.

I built one guitar (and I'm now building a second) where, like John P., I also glued on the end graft before attaching the sides to the end block -- as well as using the neck heel as a guide for gluing the sides to the head block. It all works, but I don't have the skill to maintain the shape with enough precision to then use my rigid outside molds for profiling the edges and kerfing. So the exact shape that results is a bit of a discovery and I use an adjustable mold to hold the sides for sanding. But these guitars are not intended as replicas of someone else's build, so - - - no problem.

A bit off topic, but I've added a bit of complexity to the last two builds by using fan frets and a Manzer wedge. The fan frets look cool (I think), but I'm not sure they really do much for improving the tone. The Manzer wedge, however, is definitely an enhancement. I've made the bass side of the lower bout about ¾" thinner than the treble side. As the builds were jumbos (17" across the lower bout) the thinned bass side makes it easier to hold and to play. The only construction challenge was cutting the neck heel properly.