Almost every acoustic folk guitar has a truss rod inside their neck. We can adjust it with the adjusting nut which is located at the beginning or at the end of the neck.

This device has a double utility: first of all, it gives strongness to the neck and help avoiding a string tension change. Secondly, it gives the opportunity to adjust the neck action. It’s simple: when the truss rod is not tightening, the rod is curved, and when we tight it, the rod will bulge. There’s another way of truss rod utilisation with two rods: the first one can be shortened and the other one is fixed. Usually, the strings pull the neck in one way (40kg to 80kg, even more) and this strenght is conterbalanced by the rod in the other way. In this manner, it will result as a good balance between this two tensions. The trust rod can be set, but we cannot adjust it if it’s tendrilled. The neck has to be in good condition. On the contrary, you have to go see a luthier to avoid bad surprises. For the following steps bellow, be carrefull of what you are doing to avoid broken parts on your guitar or go see a luthier !
If not, it can be disastrous for your guitar: you can break important parts of your guitar !

Guitar Neck Set :

First of all, you must learn to see the neck straightness and the neck bending: to do it, look at the neck with one eye from the bridge to the head of the guitar (or opposite) by raising the guitar neck at eye. To appreciate guitar tone, you must heard bass and treble sounds. A neck has to be flat or slightly hollow.  This setting of the neck depends on the strings you are using, and in particular their tension; you must use the strings that you are using usually and tune them correctly.

By tightening the truss rod, the neck will tend to warp; it will hollow if we loosen. There’s no problem to loosen the rod, but you will have to be careful in the other way, by tightening to much, you can break your neck. Turn twice the screw and it should be the maximum you can do !

Proceed by turning the nut one eighth clockwise until you get the result needed, referring to limit mentioned in the text above.  A perfect straight neck is not desirable as it will result in fret buzz.  A relief is necessary if you don’t want to have “buzz” on your strings. Guitar buzz is heard when the string, in its movement touches a fret.

Guitar Neck Relief

Acoustic Guitar : between 6 thousandths and 10 thousandths of an inch. The easiest way to measure this space precisely is to use a set of wedges, the same used to settle car sparkplug. You must be very careful when adjusting your neck to have to result wanted.  Don’t forget that wood works and it may takes a certain time to have all in stable place.