Design Philosophy 4

Design Philosophy 4

The Neck and Neck Joint

Saturday, August 10, 2013

In modern times, there has been a lot of discussion amongst luthiers and production guitar makers about the wisdom of using a bolt-on neck joint. Bob Taylor was the first major designer to stand out proudly and proclaim the superiority of the intelligently designed bolt-on neck. The current Taylor neck joint is pure genius, and easy to do if you have CAD/CAM technology at your fingertips. Bill Collings agrees with Bob Taylor. Collings uses a serious bolt-on neck joint.

And many smaller shops have enthusiastically been following suit. The bolt-on neck joint no longer denotes a poor, cheaply made guitar. It has been elevated to the state of the art by many of the best builders in the business.

I have been using a bolt-on, mortise-and-tenon neck joint since 2004. I use a palm router and plexiglass templates to cut the mortise and the tenon and then carefully refine it to a tight, perfectly aligned fit. The neck is attached to the neck block with two threaded inserts and hex-drive cap screws. I can now cut the mortise and tenon, and fit a neck in about half a workday. The hand cut dovetail took three or four times as long.

I have heard it said by some traditionalists that a dovetail neck joint “sounds better than a bolt-on neck”. I beg to differ with that opinion. There is about the same wood-on-wood contact with a mortise-and-tenon joint as there is with a dovetail, so I don’t think there is going to be any real functional difference, or diminution in tone with a bolt-on mortise and tenon. I certainly did not notice ANY difference when I switched to this design.

There’s no need to glue in the heel of the neck. The bolts do it all. I do use a thin line of hide glue under the edges of the fingerboard extension, mostly just to seal the joint. The idea is to fit the neck to the body perfectly, so all you really need is the two bolts to set the neck exactly in place. The bolts should never work themselves loose, because I apply a dab of white glue to the threads of the bolts to provide a mechanical bond, keeping the bolts permanently tight. If the bolts ever do need to be removed, all it takes is a strong crank with the hex driver to break the glue.

I have engineered several structural features into my guitars that should prevent them from ever needing to have a neck reset done, due to soundboard distortion or other problems often seen in well-used flattop guitars. However, one of the more compelling reasons to use a bolt-on neck joint is that if such service should ever become necessary, a bolt-on joint makes that service much easier and less invasive to the guitar.

Since 2004, I have been using a modified Spanish foot neck block in my guitars. The Spanish foot provides a very stable, structural platform under the fingerboard extension to prevent warpage of the fingerboard due to top movement.

On the top side, beneath the fingerboard extension, I install a thin, tapered wedge that provides some extra mass, further enhancing the stability of this crucial area.

The main purpose of this construction is that it allows me to set the neck angle precisely. On a radiused-top guitar, you need to be very careful that the fingerboard trajectory over the top is not aimed too high; if it is, the bridge height will be untenable. The wedge under the fingerboard extension allows me to set the neck angle so that the bridge height is optimal for good playing action and acoustic integrity. Using this design, the radius of the guitar’s top does not need to be compromised in any way, specifically, by having to sand out the radius under the fingerboard. It’s a bit of extra work to do it this way, but well worth it.

The Edwinson neck itself is a three or five piece construction, usually with a contrasting hardwood center lamination with wood veneer pin striping. I only use timbers that are cut with vertical or rift grain through the heel, because this grain orientation takes fullest advantage of the wood’s stiffness and resistance to twisting or breakage. Flat-sawn guitar necks are famous for breaking at the headstock, and are much more prone to distortion from changes in temperature and dryness.

I do not build one-piece necks. Unseen anomalies and stress points in a one-piece neck shaft can sometimes lead to warping or other distortion. Laminated necks are inherently much stronger and more stable, without adding an additional ounce of weight or mass. In my opinion, laminated necks also add some stylish visual appeal to the neck.

My favorite neck woods are Honduran Mahogany, African Mahogany, several species of Walnut, American Cherry, and White Limba. I select neck timbers very carefully for optimum hardness, density, stability, proper grain orientation, and of course, beauty. The neck of a guitar is constantly subjected to 150 to 180 pounds of constant string pull through its working life. The neck is no place to cut corners.

My necks are hand-carved, not milled out with CNC machinery. Carving necks is one of my favorite tasks in guitar making. Using spokeshaves, Japanese knives, rasps, sanding blocks, profile gauges, and various measuring implements, I can carve a neck to suit any preference. My standard carve is slim and fast, medium-C in profile, with a small bit of shoulder on the edges. This carve seems to satisfy modern tastes best, but I am certainly amenable to replicating other style neck profiles as well, to suit the player’s comfort and playing style. Click HERE to go to the “Ergonomics” page for more information on custom neck profiling.

The standard Edwinson fingerboard has a sixteen inch radius, with a 1 3/4” or 1 13/16” width at the nut, tapering out to 2 1/8”, 2 3/16”, or 2 1/4” at the neck/body joint. Again, these dimensions can all be customized to suit your preferences for fingerboard radius, width, taper, and string spread at the bridge.

I use the Luthier’s Mercantile TRSD, the best two-way adjustable steel truss rod available, in all my necks. This truss rod uses mechanical torsion to control the straightness (or degree of relief) in the neck shaft. It is very strong and accurately adjustable. In some necks, which may be subject to more than usual string tension, I will also install two carbon fiber stiffening rods, one on either side of the truss rod.

On my first dozen or so guitars, I used a hand cut dovetail neck joint, made with Japanese Dozuki saws and finely honed chisels. It was a very exacting procedure, getting a precise fit, but I took it on as a challenge to my craftsmanship. The common thinking was, a truly high quality guitar should have a traditional dovetail neck joint.

With the first few guitars, I would devote a lot of time to getting it right. It was a point of pride for me, that I could say, “Look at this neck joint, it looks like an old-school Japanese carpenter did it!”

The truth of the matter was, if an old-school Japanese carpenter had done it, it would have been cut and fitted in a half hour, and it would be perfect. My work was good, but not that good. Inside the joint, well out of sight, I had invariably placed a shim or two in there to get the right alignment and fit.

It was a skill worth learning, but ideas of form and function eventually had to lead to a more efficacious way to attach the neck to the body.

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