Kavanagh Customs

Project Guitar Help Centre: Correct Truss Rod Adjustment

Truss rods are the steel rod that runs down the centre of most, if not all modern electric guitars and basses (as well as a great number of other stringed and acoustic instruments). When strung, the tension of a guitar's strings tends to try and pull the neck forward in a bow - the truss rod helps us combat and control this.

There are only two types of adjustment that can be made to a truss rod:

TIGHTENING: which will reduce forward bow and bring the neck towards flat.
LOOSENING: which will increase the forward bow of the neck.

There are also dual-action truss rods which create tension in both directions which means there is more leeway for adjustments and, in theory, means that you could bow the neck right backwards. Although that would more-or-less destroy it.

When played, the strings of a guitar vibrate in an almost elliptical pattern where there is more movement in the middle of the string and less at the two extremities where the string is anchored (the nut and bridge). A neck with the relief set correctly will bow ever-so-slightly forward to allow for this.

checking the relief of your neck

The easiest way to quickly check the relief of your neck is to fret a string at the first and last frets. This produces a straight edge. When you look at the middle few frets (between the 7_th and 15_th fret), you should see a small gap between the bottom of the string and the tops of the frets. If the string sits against these frets it is a sign that the neck is either flat or back-bowed. If the gap is very large (more than a few mm) then this is sign that there is too much relief (the neck is bowed forwards too far) and the truss will need to be tightened.

adjusting your truss rod

Basic rules:

• Be careful - adjusting the truss rod can be time consuming and frustrating, always take your time and be very careful. The last thing you need is a broken truss rod or snapped neck. Never adjust more than a quarter-turn at a time.
• Always use the right tool. Most Fender-style truss rods are adjusted with an 1/8" allen key, but make sure you have the right size before you go too far or risk chewing up the thread of your truss altogether.
• Always adjust the truss rod with the strings in place and in tune, this will allow the strings to apply a constant amount of pressure to avoid you over or under adjusting. After an adjustment, tune the strings back up again and check the relief before the next.
• Give the neck chance to settle. It can take a short while for the neck to settle after you release the truss rod. If you tweak it and nothing happens, let it sit (with the strings tuned) for five or ten minutes and then check again. Don't get impatient.
• Know when it's time to stop and ask for professional help.

The basic principle of truss rod adjustments is the balance the amount of pressure between the strings pulling the neck forwards and the truss rod pulling it backwards to achieve a gentle and slight forwards bend in the neck. In general terms, the heavier the strings you use, the tighter the truss rod will have to be and, equally, the more the neck should bow forwards.

to apply relief to the neck (loosen the truss) and allow the neck to bow forwards more, turn the truss rod anti-clockwise:

to straighten the neck and eliminate back-bow, turn the truss rod clockwise:

Remember: never adjust more than a quarter turn at a time and always re-tune the neck and test it to judge how you're getting on before adjusting any further. If it grates, squeaks or doesn't turn take it to a technician.