the sound and the fulcrum

One of the most intimidating elements of luthiery to me has always been the neck. Fitting the neck securely, setting the neck accurately, angling the neck sufficiently… you get the idea. If building the body of the guitar was thinking in four dimensions, fitting the neck is a quantum level beyond that.

Or at least it feels that way when you begin.

In order for me to really get a handle on what I was doing here I had to break it down into a few core functions that the neck is responsible for executing. It needs to be stiff enough to hold tension (aided by the truss rod), thin enough (or thick enough depending on your preferences) to be comfortable to play, and long enough to provide proper scale length for the strings.

That’s the easy bit really. Not necessarily easy to execute, but easy to understand. As long as you choose the right wood and measure accurately you’re in good shape.The more difficult task is having a joint strong enough to hold the neck in place as it needs to be held and orienting that joint properly to provide enough backward pitch on the neck that it will allow for setting up the guitar with a comfortable and appropriate action (string height) when everything is complete.

The two most common joints are dovetail and some sort of pinned or bolted mortise and tenon. I chose the second, and that is important to note, but rather than go into detail about the mechanics of what’s happening inside the joint I want to explore what’s happening on the visible plane where the neck meets the body.

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It should go without saying, but unless you take the time to get this bit right, you might as well not do the rest. If the action is too low that it buzzes all the time or too high that you can’t play (or play in tune) then even if you’ve executed all other details flawlessly, what you have is a beautiful piece of wall art and not an instrument.

The way this is accomplished is by attaching the neck, locating the bridge (based on the position of where the nut will be) and then with the fretboard in place, running a straightedge down the middle of the fingerboard and measuring where it interacts with the bridge. If the straightedge knocks into the bridge instead of going over it you need to pitch the neck back, if it’s miles above the bridge you need to decrease the angle.

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The bridge (the saddle, really) is the primary fulcrum by which sound is transmitted into the body of the guitar, reverberated, amplified and propelled back out the sound hole. You want this to be right.

(Disclaimer: there are different and equally compelling methods by which this next bit is accomplished. I will describe mine only.)

In an earlier post I mentioned that I used a 40′ radius dish to glue in the braces to my soundboard. That effectively creates a dome of approximately 5/32″ (about .16″) in height from the level of the outer rim. This necessitates setting the neck so that the angle of where the fretboard meets the body, and the radius of the top come together to make a full 180 degree angle. In the diagram below that would be angle A and angle B.

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In a flat world those would each be 90 degrees. Lutherie is not a flat world, so in reality you’ve got something like an 89 degree angle (angle A) and a complimentary angle at 91 degrees (angle B). On mine, with the 40″ radius top those numbers are almost exactly that, give or take a half a degree.

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Part of the reason for this is keeping the fingerboard flat as it transitions from neck to body. Beyond that, the real thing you’re looking for is the clearance above the bridge. That clearance is going to be a little different with the frets installed, but without the frets, the imaginary plane extending from the end of the fingerboard (i.e. my straightedge) that I was looking for was just clearing the top of the bridge. This way, when frets and the saddle are added later, there will be enough space to compensate the action with the neck under tension.

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Oh yeah, and don’t forget to keep it straight.

That’s an important warning. Trust me. Because the way you set the angle of the neck is by slowly and carefully removing material from either the top or bottom of the mating edge of the neck joint with a chisel, feathering from a 1/32″ or 1/16″ cut to nothing and trying to keep a square edge.

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It is exactly as hard as it sounds and just when I thought I had the neck at exactly the right angle to the bridge I realized it was no longer in line with the center line of the body! I had removed more on one side of the neck tenon than the other.

So don’t forget to check, and re-check, and stop and check again because you want straight, and angled, and straight, and …

Ok, so it’s not that bad, and there are plenty of resources that will tell you how to do this work, but the main advice they all give is this:

You can only remove material at this point not put it back, so take it slow. Check your work and make lots of small adjustments instead of trying to get it right in one big swoop.

I must have put the neck on and off the body two dozen times to get to this point, but when you get there it’s a good feeling.

Bask in that feeling. Step away from your chisels. Grab something cold to drink (unless your shop is freezing, then make a nice cup of coffee or tea) and let it all sink in. You just set a neck, you cheeky bastard. Good on you.

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2 Comments Add yours

  1. Looks good, James! At some point you should try a slipper heel construction – ur has its own challenges, but you don’t have some of the paring related terror on the neck you’ve just fitted 😉

    Btw, “pitch”, “yaw” and “roll” refer to the three axis on which the neck can be out of true.

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    1. Thanks for the terms. So would pitch be the back angle, yaw the angle off axis to the centerline of the body and roll, the twist of the neck in relation to the body?

      I’m up for trying a slipper heel. Maybe if I go in for a parlor build like yours.

      Like

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