There are three primary areas on the guitar that can be (and are meant to be) adjusted.
- the nut
- the truss rod
- the bridge
Of the three, the height of the nut is best taken care of by an experienced repairman/luthier, and the complexity of bridge adjustment qualifies it for its own unique article. We will leave these out of the equation for now.
Bear in mind that both the truss rod and bridge adjustments will affect how a guitar plays and feels -- the 'action'.
In this article we'll focus on truss rod adjustment, which is something I get asked about a lot by my students and guitar-playing friends.
Truss rod adjustments need to be done before working on the bridge section. This is because any adjustment done to the height of the bridge will be negated when the truss rod is adjusted.
This is how a truss rod works:
A truss rod adds strength and stability to the guitar's neck and also plays an important role as far as string action and left hand playing comfort. When the truss rod nut is turned clockwise, the rod tightens, pushing up against the guitar's fingerboard and straightening out the neck. The truss rod nut is located either at the headstock end or at the body end of the fingerboard and it is usually adjusted with a specifically sized allen wrench, or a flathead screwdriver depending on the type of nut.
Most times, new guitars come with too much 'relief'. Using the low E string as a sort of straightedge guide, press and hold the string at the first fret (a capo in this case is invaluable) while simultaneously holding the same string down at the highest possible fret on the guitar (21st, 22nd or 24th fret depending) with the right hand index finger.
Now look closely and check for the slight gap between the 7th fret and the bottom of the 6th string.
If you can slip a 1mm pick under that gap easily and without moving the string, you have way too much relief. The gap should ideally be about the thickness of a business card.
Or, as I prefer it, with no relief at all.
If you're going the 'no relief' route, be prepared for some string buzzes around the first to third frets on the low 6th and 5th strings. This is normal, and the buzzes are usually inaudible through a guitar amp, since these lower frets are too far away from the pickups for the imperfections to be heard. If you're adjusting an acoustic guitar I would recommend going the business card route.
If you have too much relief, you need to tighten the truss rod. At this point, if you're not confident in your abilities, or if the guitar is old and hasn't been adjusted in a while, do not proceed and take your guitar to someone who knows how to do this stuff.
Loosen the 4th and 3rd strings only so you have some room to maneuver and insert the appropriately sized allen wrench or screwdriver.
To tighten the truss rod, face the truss rod nut towards you. If the truss rod nut is at the headstock end, sit with the headstock pointing directly at you. 'Righty tighty, lefty, loosey' applies here so we need to tighten the nut by turning it to the right, or clockwise. If the truss rod nut is at the body end, rest the guitar on a workbench and with the nut facing you, do the same, turning clockwise.
Adjust in small increments of no more than a quarter of a turn at a time.
If the truss rod nut seems unusually difficult to turn, do not proceed. It might be a simple a matter of lubricating the threads of the nut a little. In a worst case scenario, your truss rod may be maxed out -- in which case you have a problem and pretty much have to live with the relief. Or pay a pretty penny for a luthier to remove the fingerboard, adjust the rod, and re-glue the fingerboard.
On the flip side, if you can't fit a business card underneath the string when doing the 1st fret and last fret procedure, and your guitar is buzzing excessively and/or fretting out at the lower 3 or 4 frets on all the strings, then you have a 'reverse bow' which means that the truss rod is too tight and pushing up excessively against the fingerboard causing a hump. Loosen the truss rod by following the above procedure but turning the truss rod nut to the left or counter clockwise.
I'll cover bridge adjustment thoroughly in a later article. For now, once you have adjusted your truss rod correctly, adjust your bridge height to taste, which may be as simple as the turn of a thumb-screw in the case of a Les Paul tune-o-matic bridge, or adjusting the heights of the individual saddles on a Strat.
Go for an action that allows the guitar to play reasonably cleanly. But remember, a little string buzz is your friend! Check out Hendrix's Little Wing and you'll hear his guitar strings buzzing all over the place.
The amount of relief affects how your guitar feels, plays and sounds to a very great degree.
Stay tuned for my article on bridge adjustment where I'll talk a bit about the various kinds of bridges and some of their adjustment quirks.