Any useful discussion of acoustic guitar setups should include a close look at the truss rod, the nut, and the saddle. Each of these parts contributes significantly to the way your guitar plays, and each can develop its own set of problems. You can make many of the adjustments I'll describe yourself if you're careful and use a little common sense. If you have a serious problem with your guitar, however, you should not hesitate to take it to a reputable luthier.
The action, or string height above the fretboard, is one of the first things to check when your guitar isn't playing quite right. Many musicians mistakenly use the truss rod to adjust the action; they tighten it, thinking that by arching the neck back they will lower the strings toward the fingerboard. A tightened truss rod will lower the action, but it often leads to a neck that buzzes severely. The misguided home repair guy then starts filing away at his frets until the neck is a basket case.
The truss rod's job is to straighten the neck and compensate for the upward pull of the strings. It should not be used to adjust the action of the neck. If the action is too high at the nut, it is the nut that needs adjustment. If the action is too high in the middle and upper positions, it is usually the saddle that needs to be lowered. Let's take a look at the truss rod first. Once it is properly adjusted, we can move on to the nut and the saddle.
THE TRUSS ROD
Adjusting the neck using the truss rod is a delicate operation. If it is necessary to tighten your truss rod, We recommend setting aside plenty of time to do it. Every guitar neck should meet your playing style and accommodate a variety of string gauges. Changing to a heavier string may require a slight tightening of the rod. A lighter string may need a little backing off of the rod. Occasionally a small adjustment can be made, and the guitar will be ready to play immediately. Often, however, the neck will need time to get used to its new position.
Most factory guitars, including Taylors, newer Martins, and Guilds, use truss rods that are tightened with a clockwise turn. That is, rotating the rod clockwise brings the strings closer to the fretboard. Occasionally with double-action rods (rods that adjust in both directions), a clockwise turn may actually raise the strings. If the neck has not been damaged by heat or a long-neglected warp, a little rotation should cause the desired effect. If your neck is badly warped, get professional help.
On many guitars, the truss rod can be accessed via the headstock. For others (including the guitars I build), you need to reach into the sound hole. When the rod access is inside the sound hole, special care, and probably special tools, may be needed. Take a deep breath, count to ten, and if you're sure you want to do your own adjustment, go for it. I like to make neck adjustments with the strings under normal tension; it lets me see the real effect on the neck. I assume that most of you do not have a fully equipped shop with guitar-holding fixtures. Therefore, I suggest asking a friend to help by holding the guitar steady. First, mark the rod's nut with a felt pen so you can return it to its starting point. Then, slightly loosen the rod and see that it turns freely. If it is bound or frozen, do not try to adjust it further unless you have a great deal of experience or a deep-seated wish to break the rod and replace the neck. If it moves smoothly, put a bit of lubricant on the threads and work it in around the nut. I use a toothpick or a bit of old guitar string for this job. Then put the truss rod nut back to where it was when you started, using the mark you made as a reference.
Now is a good time to ask your friend to hold the guitar and press down gently on the nut, making the truss rod's work easier. Gently give the truss rod about a one-quarter turn. Now fret the guitar at the first and last frets and use the string as a straight-edge to see if the neck is getting flatter. The rod's effect is usually most apparent between the fifth and seventh frets. I like to see a little light between the string and the fret in the middle of the neck. If it looks right, wait a few minutes and recheck. If it seems to need more tightening, be very careful. If your rod is working correctly, you shouldn't have to crank it hard to get good results.
Tightening the truss rod compensates for the upward pull of the strings, and loosening it allows the neck to bow.
If you are getting areas of buzz in an otherwise well-adjusted neck, you may need a fret job. Fretwork is a very fussy job, demanding accuracy to less than a thousandth of an inch. It also requires specialized tools. Contact a reputable luthier to do your fretwork.
Often, guitarists adjust their truss rods when what really needs work is either the nut or the bridge. If the first few frets feel stiff and hard to play, the nut probably needs work. A nut that is not cut deeply enough will make chords in the first few positions difficult to play. A nut that is too deep will buzz like a sitar. If the strings are hard to tune, again the nut may be to blame. Although it can be tricky to make a nut play well, if you are careful and take your time, you can probably improve the playability of your nut. You will need a few unusual tools for this job, so unless you want to make a small investment, go to a luthier.
Very fine, small files allow you to make the grooves for the strings with great precision. It is the careful fitting of these grooves that makes the nut play well and sound clean. Nut files come in many sizes to match the diameters of guitar strings. You don't need all of them. You can make each file do the duty of many by rocking the file slightly as you work. Pay special attention to the shape of the groove. The object is to end up with a groove that neither binds the string nor causes it to buzz. If you file too deeply, you can fill in the groove with a little super glue and start over. Be careful, wear eye protection, and don't overdo it. Place one tiny drop in the groove and sprinkle a bit of baking soda over it as the glue sets. This will harden into a very good simulation of bone, letting you re groove the nut as if you had not messed up. Only you and I will know. Gently file until a scrap of paper from the Yellow Pages will slip in between the first fret and the string when fretted at the second fret.
If your nut is the right height, you should be able to fret the second fret and just fit a scrap of paper from the Yellow Pages between the first fret and the string.
Even a well-fitted nut can bind and mess up your ability to tune. One evening I received a phone call from Scott Bennett, who had been touring the world and recording for 20 years on a guitar I made him. He was backstage at the Boulder Theater waiting to go on, and the D string on his guitar was binding and making a little squeaking noise whenever he tuned it. You've probably had the same problem. I immediately drove across town to fix his nut. After a moment's diagnosis I took out a no. 2 pencil and put a little graphite under each string in the groove of his nut. The problem was solved. If you don't overdo it, you'll find that a bit of graphite (pencil lead isn't really lead, you know) can work wonders to stop strings from binding.
If your action still feels wrong and the neck has been properly adjusted, it is time to look at the saddle. Lowering the action may require removing a bit of material from the saddle. Raising it may mean a new saddle or a shim under your existing saddle. If some strings are fine and others are too high or low, you should consider re-contouring the top of your saddle. Otherwise, it is simpler and safer to make adjustments to the bottom.To raise the action, I recommend using a new, properly fitted saddle, preferably made of bone although many new synthetics are available.
It is not always practical to have a new saddle made or to make one yourself. If you can't get one, We suggest shimming what you have. Hardwood veneers are a good choice and readily available. Veneers are commonly .032-inch thick. They can be sanded if you need a thinner shim or stacked to achieve a taller one. At least half of the saddle should be within the bridge slot or it may tip forward or even break the leading edge of the bridge. Be extra careful if you have an under-saddle pickup. Changing your saddle could affect the string-to-string balance.
If you need to lower the height of your saddle, sandpaper attached to a flat surface works well. Simply slide the saddle back and forth across the abrasive, being careful to keep the bottom of the saddle flat. It helps to mark with a pencil how much material you wish to remove and then sand to that mark.
Setting up your own guitar can be very satisfying. You will be most successful if you take your time and take extra care with each step. Good luck.