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A R T I C L E S
The Importance of a Correct Neck Angle
by Bruce Morrison
The angle at which an instrument's neck is affixed to its body is the single most important factor in determining how well the instrument will play and sound. Those instruments which play and sound the best have a correct neck angle. Yet, no two instruments share the exact same geometry. The neck angle must be determined for each individual instrument including instruments of the same make and model with consecutive serial numbers.
The force produced by a correct neck angle and a proper set up determines how much string energy is transmitted to the soundboard. If the neck angle is too shallow, the bridge saddle won't be tall enough to create the correct angle of downbearing. Formed where the strings break across the bridge saddle, the angle of downbearing determines how much string energy is applied to the soundboard. A significant loss of tone and volume along with a string action that feels rubbery result when a soundboard isn't driven by as much string energy as it should be. Yet, when the neck angle and resulting angle of downbearing are too great, the soundboard, overloaded with string tension, can't vibrate as freely as it should, inhibiting the production of sound.
The neck angle is the primary factor which determines an instrument's playability. When setting an instrument's action, the adjustments of the truss rod, saddle height, and depth of the nut slots are all made relative to the neck angle. Assuming that the fretboard and frets are as they should be, with the correct neck angle, the action can be set very low.
To check a guitar's neck angle you'll need a 24" precision straightedge. A wooden yardstick lacks the accuracy to do the job. With the neck relief correctly set and the instrument tuned to pitch and held in playing position, place the straightedge in the middle of the fretboard between the 3rd and 4th strings. The bottom of the straightedge should just kiss the top of the wooden bridge. This indicates that the top of the bridge and the tops of the frets are aligned at the same height. This insures that the strings and saddle will have the right height to create close action and the right angle of downbearing. However, in most cases the end of the straightedge will bump the front of the bridge indicating too shallow a neck angle.
Depending on where the straightedge contacts the bridge, there are two repair procedures. One is called a neck reset. The angle of the neck to the body is altered by removing a calculated amount from the foot of the heel, tapering to zero at the neck/ fingerboard joint. That calculation must be made with the instrument tuned to concert pitch before the neck is removed. After the required amount has been shaved from the heel, the neck is re-glued at the correct angle. While that all sounds fairly straightforward, the neck's angle, centerline, height, twist and the fit of the dovetail joint and of the heel to the body must be worked simultaneously. A ramp is then created in the soundboard beneath the fretboard tongue so that the fretboard will mate to the body without an extreme downward turn of the tongue.
When the neck angle is within tolerance at the heel but not within tolerance close to the nut, a plane and re-fret is the solution. That procedure, detailed in my article "Tension Rods and Neck Relief", involves removing the lower frets and planing the fretboard back to within tolerance before new frets are installed.
In my previous articles I've spoken about the importance of having the set up and bridging correct. Having the correct neck angle is even more important.
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