How to make truss rod adustments on your guitar

Sometimes we string instrument techs take it for granted that all guitar players know how to make simple adjustments to their instruments. I am a believer in instructing players how to take care of their guitars and make simple adjustments when they are needed. This allows me more time in the shop for the major repairs that just shouldn’t be rushed, especially if I’m working on a valuable instrument. This is one of the main reasons for this article, to help people become more knowledgeable about their particular musical instrument and make those simple adjustments when needed. One of the easiest adjustments to make on most guitars is a truss rod adjustment.

Truss rod adjustments are not rocket science. Minor adjustments of the truss rod are nearly always safe to make. I say nearly always as I don’t advise beginners to make adjustments if the rod seems stuck or gets extremely hard to turn. These two problems could lead to major repairs if you have not had experience of what can cause the problem and how to correct it. If you should try making small adjustments on your guitar and run into one of these problems, then you should by all means seek out a good repairman. Good quality instruments will need periodical adjustments to the truss rod and rarely exhibit any problems in doing so. It’s usually very inexpensive instruments or very old instruments when problems surface.

Checking To See If A Guitar Needs A Truss Rod Adjustment

The necks on guitars are under a lot of constant strain from the string pressure exerted on the instrument and this tension will nearly always put a small amount of “bow” in it. Many times you can see this bow by holding the guitar with the head stock near your face and the body away from you, and sight down one of the edges of the fretboard towards the body. Even though you can many times see a slight bow in the fret board using this method, it’s not always safe to assume what you are seeing is correct. There are some other factors that can give the illusion of neck bow, so I rarely use this as an indicator of problems. The easiest way to check for neck bow is to put a capo behind the first fret, note the top string where the neck joins the body and look for string clearance between the top of the frets and the bottom of the string at about midpoint between the capo and neck/body joint. This method, in effect, creates a straight edge of the string and neck bow becomes quiet obvious.

Here is where most people make the wrong assumption, and that is that any neck bow is not good! The fact is, if the fingerboard were perfectly straight, you would most likely have some severe string buzz.

When you were young and swung a rope back and forth that was attached to a stationary object, you probably noticed that the rope would exhibit a curve in its length when at either extreme of the swing. Guitar strings are affected in the same way when they are played, or put into motion. If we imagine some of your playmates standing in a straight line next to our rope as you were swinging it from side to side, you can see the rope striking those about halfway down the rope because it’s arc is greater there than it is near you. This same effect happens to the strings striking the frets on a guitar when the neck is too straight.

In the above game, if all the children stayed in a straight line and were to step back from the rope to the point that the middle child was not being struck, then the children closer to you and the object it was tied to would be much farther away from the rope at its greatest arc than the children at the middle. This would be similar to raising the strings away from the fret board (assuming the fret board is straight) to prevent the strings from striking the frets in the middle of the neck. You have eliminated the problem of the strings striking the frets in the center of the fret board but have caused excessive string clearance at both ends of the strings, just as the children at the end of the rope created a much larger margin of safety than needed by stepping back more than was necessary.

Now imagine all of your playmates stepping back just enough to keep from being struck by the rope. They would have then formed an arc very much the same as the arc of the rope, and no one would be any farther away from the rope than any other child.

This is exactly what we need to do to the fretboard of the guitar, and we do so by allowing the fret board to have a slight bow in it. Too much and it becomes difficult to note the strings in the middle section of the neck from too great a safety margin. Too little and you will have string/fret buzz.

So, How Much Is Enough?

Several things can have an effect on finding the correct neck bow. Electric guitars can usually benefit from a straighter neck than an acoustic guitars. This is true due to any slight string buzz that would show up is not normally heard through the amp. Generally, lighter gauge strings will create fret buzz easier than heavier strings. Heavier strings are usually much stiffer than light gauge strings, all things being equal, and will have less arc to them because of this. I can usually set up a guitar with a lower action if I use heavier strings. Light-gauge strings, especially extra lights, usually require a higher action due to their flimsiness and more pronounced arc when excited.

The normal guitar player rarely has the special gauges needed to determine string clearance, but one can get by using a spare 1st string as a gauge for most needs. Use it to get a good idea of what the clearance should be at the midpoint of the fretboard, measured from the top of the closest fret to the bottom of the string and adjust the truss rod accordingly. The important thing to remember is that turning the truss rod clockwise, or tightening the rod, will straighten the neck and counter-clockwise, or loosening the nut, will allow more bow. If the rod seems unusually hard to turn, do not force it. Have a guitar tech check it out for you. It will normally be a little stiff as it’s most likely having to overcome the string tension, but not excessively so. Turn the rod approximately 1/8th to 1/4 turn at a time and recheck the clearance. Rarely should you have to turn it more than one full turn. If at one full turn the neck has not been corrected, take it to a guitar tech. You don’t want to break it! Some techs recommend loosening the strings before tightening or straightening the neck, but I rarely do so anymore. I will loosen the strings if the truss rod is harder to adjust than usual to relieve some of the tension on the neck, especially on 12 string guitars and basses. This is one of those times that a little knowledge can prevent a lot of headaches.

Most new guitars come with allen wrenches to do minor truss rod adjustments. Gibsons and some others require using a 5/16″ nut driver. Keep it in your case for those minor adjustments.

Making minor adjustments of guitar truss rods can improve the playability of your instrument if done correctly and can give the player a greater level of confidence in doing so himself.




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