Step 1. Check the neck’s “Relief”
This section is mostly for steel string acoustic readers because to adjust relief, the guitar’s neck must have a truss rod. However, some classicals and nylon crossovers have truss rods so stay with this step if you do. Look under the soundboard from above the sound hole and back towards the fretboard. Does your guitar have a little bolt under there that looks like it could be turned with an Alan wrench or some other similar tool?
Guitars need to have a bit of a bow under the force of the pull the strings have between the headstock and the bridge. Total string tension on classical guitars is 80+ lbs. On steel string guitars it’s 180 lbs. for medium gauge. This tension is enough to give the neck a little bit of a bow. But, too much of a bow will make for bad action and you’ll be less likely to play your guitar. Notice the big difference between the tension classical and steel string acoustic strings? The much higher tension require a truss rod.
- Put a capo on the 1st fret
- Hold down the low E string at the 14th fret.
- Use a business card to check the string’s height (distance between the top of the fret to the bottom of the string) at the 6-7th fret. Try to slide the card under the string at that area.
- Does the card slide under the string with considerable space left under the string? If YES, that means the relief is too severe. Tighten the trust rod by moving it only 1/4 turn clockwise. Repeat the 1st three steps and re-check, repeat as needed until the string’s height is just enough to slide the card under.
- Does the card not slide under at all? but hit’s the string instead? If YES, the neck does not have enough relief. Loosen the truss rod in only in 1/4 turn increments, re-checking and repeating as necessary until the card just slides under the string in the 6-7th fret area. Keep notes as you go and notice the changes. Try to sneak up on the perfect setting with slow, patient decisions.
With the relief set, move on to the Action at the 12th fret section if you are not changing the nut on your guitar. If you need to install a new nut proceed below.