Setting up the Guitar.
The art of setting up the guitar ( and all fretted instruments ) is more complex than you think and a thoughtful approach to the job will pay dividends as once a mistake is made, recovery will be difficult.
It's an unfortunate fact of life that the modern mass produced guitar is built on an assembly line and time is of the essence. The setting up stage is not a procedure that a machine can do and this fact means that with a few rare exceptions, most new guitars arrive at the retailer with a higher action than is ideal. This means the strings will not buzz and the guitar is apparently faultless.
The ease with which a well set up guitar can be played makes all the effort taken worthwhile and the following information should help the process.
The set up should proceed logically, starting with
The Fingerboard.
The amount of movement a string exhibits when plucked is called its excursion. This movement is obviously greater at the mid point than the ends and the fingerboard should be contoured to allow for this.
Perhaps at this point, the function of the truss rod should be understood. The truss rod is not designed to impart a curvature, it is simply there to compensate for the tendency of string tension to bend the neck up.
The contouring of the fingerboard, known as the relief, is achieved on the best instruments before frets are fitted but for the completed guitar, the procedure is as follows.
Firstly, is important that the frets are even as any high frets will cause buzzes. To true the fret tops, obtain an oilstone that has never been oiled. These are available from engineer’s stores and are designed to be used with water. Lightly dress the frets with this until each fret shows the stoning mark. The profile of the fret can be restored with commercially available fret files or if only slight flats have been put on the frets, 800 grit wet and dry abrasive held with fingertips will do the job.
With the guitar at its usual tuning, press the 1st string at the 1st and 12th frets simultaneously. If the little finger of the left hand is used for the 1st fret, that leaves the left thumb free, at full stretch, to press the string around the 6th fret. The clearance between the string and the 6th fret should be between 1/4 and 1/2 the thickness of the string. The procedure is repeated on the 6th string and an impression of the existing relief ( or lack of it ) can be obtained.
If the neck is too straight, slacken the truss rod by 1/4 turn (Anti Clockwise when facing the end of the rod )and check again. If there is too much relief, the truss rod can be CAREFULLY tightened by1/4 turn and the results noted. The truss rod as I said is not designed to impart curvature and it is possible to either strip the thread or break the rod before the required curve is reached.
Many mass produced guitars have poorly fitted truss rods, which have little or no effect.
If these remedies do not work, the oilstone can be used to give the relief by reducing the fret height where required.
Generally, if the guitar buzzes in the lower positions, the neck is too straight and vice versa.
The Nut.
Sitting quietly at the end of the fingerboard, the nut is more important to the action than it appears and is responsible for many guitars playing badly in the first position.
If the nut is incorrectly cut, the strings may either buzz when played open if too low, or cause poor intonation and tone in the lower positions if too high.
The theory behind cutting a nut properly is simple - the slots should be cut as low as possible and yet not allow open string buzzes!!!
To achieve this happy state, the technique is as follows.
With the string at normal tension, press a finger between 2nd & 3rd frets. This bends the string down from the nut to the 2nd fret. The clearance where the string passes over the 1st fret should be in the region of 1/4 the thickness of the string. For a 1st string of 12 thou. the clearance would be 3 thou. These measurements are normally gauged by eye although feeler gauges could be used.
What we are achieving with this operation is allowing slightly greater clearance above the first fret in order that the open string can vibrate cleanly. The extra clearance is required because an open string vibrates more strongly than a fretted string.
The slots should be slightly angled back to the machine heads and should be a good fit to the strings.
Most mass produced guitars are fitted with plastic nuts, which are not great to work with. Bone or Ivory (recycled of course) are much better.
The Bridge
After all this has been done, all that is required is to set the saddle in the bridge to the required height. I say required because the height of the saddle and thus the overall action height is dictated by the playing style.
The delicate fingerstyle player can afford a very low action with light gauge strings and will be able to force a buzz anywhere on the fingerboard by playing harder. At the other extreme, the heavy playing country flat picker will need heavier strings, a higher action and will be able to play hard without any buzzes. The choice is now dictated by the player not the limitations of the instrument.
Should the saddle need to be lowered a lot, and the guitar has an under saddle type transducer, it may be necessary to cut channels in front of the bridge pins to maintain a reasonable angle over the saddle. Too little angle may cause poor amplified response.
Once the required action has been achieved, a final check should be made to ensure the intonation is correct. The string is stretched when pressed down to the frets and this makes it play sharp. The higher strings tend to sharpen less and overall, a higher tension set will sharpen less. This is why most guitar bridge saddles are slanted to give a longer string length to the basses. It can be seen, then, that the choice of strings needs to be made before the intonation can be set accurately.
With the instrument tuned to the required pitch, first press the strings down over the nut and saddle to ensure they are not being affected by their natural stiffness and vibrate cleanly - new strings, particularly the lower ones tend to curve over the saddle initially. Then either by ear or preferably with a meter, play the 12th fret harmonic. This should be identical in pitch to the sound at the 12th fret. If the fretted note is sharp, the open string length needs to be longer and vice versa. To lengthen the open string length, file an angle back from the front edge of the saddle so the string sits further away. Do the opposite if it is flat.
These adjustments are too fine to correct any major intonation problems and it may be necessary to fill the saddle slot with a matching hardwood and re-cut the saddle slot. This would be best left to a professional.
The information given here is the result of over thirty year’s experience of building, repairing and playing guitars and related instruments.
Good luck.
Neil