Your Guitar Set Up - Step 1 – Check and Adjust NeckThe first step in any acoustic guitar repair set-up is to check and adjust the curve of the neck. This is commonly called as the "neck relief".
Here is an easy way to check the curve of the fretboard in the playing area:
With the guitar tuned to pitch, hold the guitar in the playing position and depress the low E string at the 14th fret with the index finger of one hand.
While keeping the string down on the 14th fret, depress the same string at the first fret with the index finger of your other hand. The bottom of the E string becomes a straight edge.
Sight the area under the string around the 5th to 7th frets. If the neck is correctly tensioned there should be a hair breadth of space in the middle of this area between the bottom of the string and the top of the 6th or 7th frets. This gap gradually diminishes to zero as the string reaches the 1st and 14th frets.
You can evaluate the fretboard under each of the strings using this method. It is not unusual to get slightly different readings from string to string, though ideally they are all more or less the same.
Most repair techs will adjust for a slight forward bow. Most guitar truss rods enable a lifting of the neck in the center of the playing area by tightening, or turning clockwise, the truss rod nut.
Your Guitar Set Up - Step 2 – Check and Adjust Nut Slot Height
Once the neck curvature is set, the string height at the nut should be checked. With a correct neck curvature, there is one right setting for each nut slot. Each nut-slot should sit no higher than the preceding fret to assure a complete acoustic guitar repair.
Some builders use a “zero” fret, and a nut sits behind the “zero” fret only to guide each string on its path to the tuning peg.
On most guitars the string is both guided and height adjusted at the nut. A string which sits too high at the nut can either feel too hard to push down, or even play sharp. Ideally it should be lowered till it also feels comfortable to depress.
If the height of the 1st fret above the fret board is known, a metal gauge of the same height as the existing frets , laid in front of the nut can be used as a guide. With a file of appropriate width, the nut slot is lowered until the file touches the gauge.
Without a gauge, the setting is done by eye. To calculate the appropriate height, depress the string between the second and third frets with your middle finger and sight back to the first fret.
If the string rises above the first fret more than the thickness of a piece of paper the slot should be lowered until just this amount of gap is apparent. While holding the string down between the second and third frets with the middle finger, the index finger can be used to depress the string at the first fret to discern this gap.
If the string sits on the first fret, while the position between the second and third frets is being held down, the slot is probably too low for this acoustic guitar repair and the string will probably buzz if plucked “open.”
Your Guitar Set Up - Step 3 – Check and Adjust Saddle HeightOnce the neck curvature is correct, and the height at the nut is set, (and never before these steps are taken) the height of the bridge saddle can be set.
This acoustic guitar repair adjustment is made by filing or sanding the saddle piece to give the desired height for each string. There is no “correct” height of the strings over the fretboard.
Playing style determines the appropriate setting. A light finger-stylist can get away with very low action, whereas a blue grass flat-picker will prefer it quite a bit higher.
A good “shop setup” for acoustic guitar is generally acceptable for both moderate flat-picking and finger-picking, but favoring neither.
Wrap UpThese are the three basic steps in the set-up of an acoustic guitar. They must be done in this order: neck then nut then saddle. This information is meant to educate - it is not intended that you would do these adjustments yourself. For the information on this page I credit Steve Carmody who has set up thousands of guitars.