The Neck / Body Union

One Way to Get it Done

Aloha! Today I take some time to muse over the importance of the many things to consider while constructing the neck / body union. From my first build to my latest, it has challenged me each and every time, and I have struggled to explain the complexities of it to my students or to myself. When I think of neck /body unions, I immediately think of the joint itself, and that means a dovetail. I give credit for many of my building methods to a master archtop maker who wrote an excellent book on the subject, Mr. Robert Bennedetto. He stated that the dovetail joint was his mating method of choice for the neck attachment, and well worth the extra effort. I bought in almost immediately. But in my first half dozen of my builds, I had chosen the easy path, and simply glued the neck on without a care in the world, and sandwiched a fretboard over the top, and also onto the top of the soundboard for a few frets. I didn’t even bother to install a biscuit to reinforce the joint. No dowel to pin it in, no bolt and anchor to make it removable…ignorance was bliss. More than a decade later, and with several dozen builds now behind me, I give this part of the process a great deal more very close attention.

When I began making flat top ukulele, we used Kamaka’s old method as previously described. Sure, we had a fine sawcut on the end grain, and the glue wasn’t likely to adhere all that well, but we glued the neck on anyway. Then the fretboard, thinking, if it’s good enough for Kamaka for the last 75 years, it should be good enough for me. And, oddly enough, it was! Most of my early ukes are still in one piece, and so are 90% of all Kamaka’s ever built using this technique. My brain wanted it to be more intricate and sturdy looking, but experience says… Keep It Simple (Stupid).

If I wanted a few more choices to attach the neck to the body, I might start with things you see on antique instruments. Like nails! Yes, it has been done. Probably most everything has been tried. Alternatively, making a channel into the headblock, and also the neck, could set you up to install a wooden biscuit between the two. That would increase glued surface area, and introduce a new shear plane to fight against. One could also put a dowel through both to cement their relationship a little better. Getting progressively more difficult, many folks choose to use a bolt on neck. This involves preparing for a bolt to go through the headblock from the sound hole direction ( through a pre-drilled hole), and into a threaded brass receiving end embedded into the neck’s mating surface. And then, there are other methods, like the Spanish heel, where the neck has the sides literally built into it, featuring that neck as the central focus of the instrument.

For me, and many others, using the dovetail joint at the neck / body union, is the way to go. I like a wedge shaped dove… when it hits bottom, it is locked in solid. It is as strong as you can ask for. It gives you adjustability in the vertical dimension, and repeatability to make late changes. And, we have modern jigs to make them easily. But before I go too far, I should note that quite a few luthiers have kept with traditional dovetails in that they cut them by hand. They claim it gets easier every time, carefully marking out parameters and then removing all that is not needed with fine saws, chisels, and a fair amount of skill. They laugh at the setup that I have… Fixtures to hold the body firmly on a centerline while routing the female dove with a router, pushing a 14 degree dovetail bit near a plexiglass template. And then making a male dove onto the neck’s end with a similar device and template, adjusting the length of the dovetail to suit the vertical needs of the union.

And that brings us around to the wide angle view of the entire scenario and what it takes to make all the decisions that come into play with the dovetail joint. Let’s take a look at some of them. If I remember correctly, there are seven or eight parameters that affect the neck / body union. First and foremost, the center of the neck must aim at the center of the instruments bridge. Most of the time, that’s the centerline of the instrument also, but not always. Second, it has to elevate the fretboard to a height that is compatible with the bridge and saddle that you plan on using. Do not simply cut your neck angle at ninety degrees ( or any other number), and hope for the best! Most times that cut will be unique to that circumstance, and you must also take into account… thickness of fretboard, size of frets, action, number of frets, total length of completed fretboard, support underneath a floating fretboard extention, what kind of bridge you plan on using, and if it will be electric, and also exactly how tall will it be when complete. More? I am sure there is ( like scale length, and breakover angle), but that’s enough for now.

I finally decided that for most of my smaller builds, a 5mm thick fretboard would work well. That made part of the equation static. I can measure my fret height if there are any questions or if I am using unusual stock. Action is also pre-determined to a large extent, lower for electrics, and higher for nylon strings. With my floating fretboard extentions, the number of frets total, and to the union ( usually 14 or 15), make a very big difference. Then, there is the bridge. If I make a simple bridge, it can be much lower than if I make an adjustable bridge. Six or eight millimeters in height can make a huge difference in the scenario. So, before I can make that cut for neck angle, I need to know a lot about what will be a unique build well before I get near a saw.

I don’t mind admitting that I struggled with these parameters for years. At first I could not understand why five different tenors needed five seperate angles to make the geometries work. Then I realized that, for starters, each domed soundboard had a unique height above the kerfing. Not radically different, but not carbon cutouts either. But it took me until just a few years ago to utilize a technique that gets me very close to a perfect fit. And believe it or not, the entire situation boiled down to a small detail that seeemed totally unimportant. For me, that was the open space below my fretboard extention, out there at about fret 20 or so. I had decided that a 5mm fretboard felt right. Then I chose 5mm thick of extention underneath it for support ( visible from the body end of the neck), and it finally dawned on me that my model hinged on the open space below that extention, the airgap. I chose 3mm, and it all fell into place.

Now, for each new build, I mock up a fresh “fretboard and action simulator” to rest onto the bare neck with it’s ‘likely, ball park”neck angle cut, clamped to the head block, and projecting “too tall”. I take a small, clean piece of thin plywood and precisely draw out a 5mm fretboard to the number of frets I plan on using. Then I add fret height, and then action at the 12th fret (about .100 in.). From the nut area, I make a line representing strings, from nut zero through the 12th all the way to the saddle, incorporating action. At the saddle, I make two lines for breakover angle towards the tailpiece ( one needs downward pressure); one at14 degrees (best case) and one for 12 degrees. Under the saddle, I measure the action again. it should be double what it was at the 12th, so the straight line marking the fret tops would be .200 below the strings. When that checks out, I mark off the bridge height below the saddle. I know this because I already made the bridge. I am not leaning on hope, that I can make a bridge 18mm tall at the center, I have it in hand. And now, that open space… fretboard at 5mm, support 5mm, open space 3mm. Done. It has all come together, from Scale length to action and several considerations along the way, the theory portion of the fit is over. Take that template over to the saws and cut away anything below the fretboard, the open space, and the base of the bridge.

Now is the time to be practical and make it work. The body has a female dove into the face of it, the neck has yet to be fitted with one. The neck gets clamped to the headblock at approximately the right height and has an extra long end, so we can make a few cuts to get this right. We put the action simulator directly onto the the top of the neck, as if it were a fretboard, and hope to see the two defined points, the bridge base, and the open space, touching the soundboard. If it’s not right, we decide what has to be done, and dismantle the simulator, make a cut, and try again. Soon the cut is near perfect, what is known as the overstand becomes measurable ( how high above the soundboard the fretboard needs to be) and even the centerline projects to center of body. The cuts are made with an excellent quality 12 in. compound miter saw with a finish blade. Finally, that first important cut is made while doing the math so that the cut puts your fret of convenience at the body union. Hoping for the 14th at the union? Do the math, know how thick the dovetail will be, and measure twice. Later, we put the neck into the dovetail jig with it’s centering pins and adjustable template, and fire up the router again, creating the dovetail, and hopefully it’s a little too long, if anything. Trial and error has us fitting the dove several times, and trimming it back each time until we get a near perfect fit… it is easy to re-install the neck into the jig, and move the template a short distance to try again, slowly shooting for perfection.

It projects right down the center. The simulator lays on the neck and those two important reference marks rest on the top, while the 14 or 12 degree breakover lines point to a tailpiece height that can work for you. The hard part is over.

But what a journey! So many considerations, and each instrument is unique. It can be the most challenging of the decisions that an archtop luthier has to make, and it is easy to make a very small but hugely important mistake along the way. Certainly there are a few operations that are more enjoyable and less stressful during the building process, but every time I get to thinking about what for me has been the hardest part of lutherie to explain… I immediately think of the Neck / Body Union. Cheers, Raven