Part Two of this article covered how to properly adjust truss rods and optimize the relief of a bass or guitar based on a standard reference. Part Three will present specific examples describing how to correct certain types of fret buzz, upbowed, backbowed or twisted necks by adjusting a truss rod. Part Three will also describe how to fine-tune a truss rod to optimize an instrument's relief based on its individual characteristics. It is recommended that you read Parts One and Two of this article before reading Part Three. Please read the following article in its entirety before making adjustments to your own instrument.
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Correcting Bowing, Twisting and Fret Buzz
The following examples will describe basic truss rod adjustments that will correct some common problems. Keep the following in mind while reading the examples:
1. Truss rods do not lower the strings, nor does their adjustment necessarily improve the instrument's action in every situation.
2. Truss rods only change the curve/bow of the neck. Adjusting the truss rod will not bring the strings closer to the neck, but in some cases may bring the neck closer to the strings, improving action.
3. Adjusting the truss rod alone may not be enough to eliminate fret buzz. Certain fret buzzes may only be corrected by raising the action, leveling the frets, etc. If the truss rod adjustments in this article do not cure the fret buzzes of your instrument, consider consulting a profession al luthier.
Example 1: Severe Relief
Playing the frets in the middle of the neck in Figure 1 is likely to cause fret buzz and the amount of relief may adversely affect the instrument's action. To fix this problem, tighten the truss rod (don't forget to follow the procedures for proper rod adjustments detailed in Part Two of this article).
Once you have adjusted out all but a small amount of relief, check the tuning and play the instrument. If the instrument has developed new fret buzzes, you may have taken out too much relief and should loosen the rod slightly. Proper relief generally improves action and reduces or eliminates fret buzz.
Example 2: No Relief
The instrument depicted in Figure 2 may buzz when its strings are played open or fretted, especially if its action is relatively low or the frets are uneven. If the instrument does not buzz at all, its relief is already optimized. If there is fret buzz, loosen the truss rod slightly, re-tune and play the instrument, checking to see if you have eliminated the buzz. Repeat until the instrument no longer buzzes, at which point you will have optimized its relief.
Example 3: Severe Backbow
The guitar in Figure 3 playing any fret below the middle of the fretboard probably causes buzz. If the backbow is severe loosen the rod significantly, if not all the way, until the neck shows a slight amount of relief. A severely backbowed neck may take as much as a day or two to adjust to the lack of rod tension; be prepared to set the instrument aside and wait.
If the backbow does not go away, do not despair. If the instrument has a two-way (double action) truss rod, you are in luck! A two-way truss rod can cause a backbow or an upbow to the neck. To add relief to a neck with a double action truss rod, simply continue to turn the adjuster in the loosening direction until the neck has a small amount of relief. If the instrument has only a single action truss rod and the neck does not show any relief, consult a luthier or repair technician.
Example 4: Twisted Neck
Twisted necks cannot normally be corrected by either single or double action truss rods alone. Twists can be taken out in instruments with two independent truss rods in the neck. The dual rods can be independently tightened to correct the twist. For example, a clockwise twist could be corrected by tightening the rod on the bass side and/or loosening the rod on the treble side. Dual truss rod systems are relatively rare howe ver, so other means to correct the twist must be used. A twisted neck can sometimes be corrected by changing some of the strings. Adding heavier gauge strings to the side that has less twist may improve or correct a twist. Conversely, switching to lighter gauge strings on the side with more twist may have a similar effect. If the latter or former methods fail alone, they can be combined to have a greater effect on the twist.
Fine Tuning a Truss Rod
Most guitar and bass necks require about a business card's thickness of relief to optimize their performance. Every instrument has its own unique characteristics and quirks however, and most can be further optimized by carefully fine-tuning their truss rods. To fine-tune the truss rod of your instrument, first adjust it until it has a business card's thickness of relief. Next, play all of the frets for each string, listening for fret buzz.
If there is no buzz:
1) Tighte n the truss rod slightly, further reducing the relief.
2) Re-tune the instrument, allow the neck to adjust to the increased tension and play all of the frets for each string, once again listening for buzz.
3) Repeat steps one and two until you notice some fret buzz, then loosen the truss rod just slightly enough to eliminate the buzz.
If there is buzz:
1) Loosen the truss rod slightly, increasing the relief.
2) Re-tune the instrument, allow the neck to adjust to the decreased tension and play all of the frets for each string.
3) Repeat steps one and two until the fret buzz is eliminated.
Once you have followed through with the above steps, you will have successfully fine-tuned your instrument's truss rod.
Given the information in Parts One, Two and Three of this article, you should now have a fairly thorough understanding of truss rods and how to use them to improve your instrument.
Copyright An thony Olinger, Xylem Handmade Basses and Guitars 2008.
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