Truss Rod Adjustment
by David Means
This is the kind of simple adjustment that every player ought to learn to do for himself. And as long as one is forewarned and uses reasonable caution, there really isn't much danger. If there were, they wouldn't pack the wrench the guitar! There are three main cautions to observe when adjusting the truss rod:
- make small adjustments, certainly no more than a quarter-turn (preferably an eighth) and observe the results of each adjustment before making another
- realize that it may take a full day for the full result of the adjustment to show up in the neck, and
- don't apply excessive force if the nut doesn't turn reasonably easily (you could break the truss rod, resulting in a very expensive repair).
What the truss rod does is to adjust the "relief" of the neck. Relief is the term used to describe the amount of desired "upbow" in the neck between the body and the peghead. Most players feel that the neck should have a little bit of relief (not be perfectly flat) to accommodate the fact that, when strings vibrate, they have their maximum excursion in the middle of their span. If you have a very light touch as a player, you might be able to get away with a perfectly flat neck, but only if the frets are perfectly "dressed." The truss rod allows you to adjust for minor differences in neck bowing caused by using string gauges other than what the guitar was initially set up for. Don't just assume, though, that you can use medium or heavy gauge strings if the guitar came with lights -- the guitar may not be designed to handle the extra tension.
Here's how to tell if your guitar might need a truss rod adjustment: simultaneously fret a string at both the first fret and the "body fret" (usually the 14th), and note the clearance of the string above the 7th fret. If the string rests on the 7th fret, the truss rod may be too tight. If the 7th fret clearance is much more than about the thickness of the cardboard of a matchbook cover, the truss rod may be too loose.
If the relief of the neck checks out all right using the above procedure, but the strings are uncomfortably high above the 12th fret when unfretted (high "action"), DO NOT try to lower them by tightening the truss rod -- you'll only further screw up the playability of the guitar, and quite possibly break something. In most cases (especially with newer guitars) this problem is best cured by lowering the height of the bridge saddle.
In every guitar I know of, the truss rod is tightened (to lower the relief clearance) by turning the trussrod nut clockwise when you are facing the adjustment end of the neck. Turn counterclockwise to increase the relief.
I would humbly suggest that part of your guitar education should consist of learning how your instrument works, how it reacts to its environment, and how to adjust it yourself. A luthier who frequents this newsgroup, Charles Tauber, recently wrote a comprehensive and excellent treatise on guitar adjustments which he posted here. You should be able to find it in the archives. It was entitled "Basic Guitar Set-up 101" and last posted on May 16. There are also a number of published books and magazine articles that cover the subject.