This is the first in a three part series on what makes a guitar have killer string action. For those who may not know, a guitars action is essentially its string height over the frets. A guitar with strings that are close to the frets make the strings easier to push down and play. People live with poorly playing guitars simply because they feel there is no alternative, but in reality there is a lot you can do to maximize the playability of your current instruments.

This series of articles will not focus on teaching you to make these adjustments yourself; many times this is best left to a professional. What you will learn is what makes a guitar play well and what you can look for to see if your guitar is in or out of adjustment.

The truss rod is perhaps the most critical part of your guitars setup. Any other measurement or adjustment will be influenced by the truss rod, so it is critical that your truss rod is right! Signs of an out of adjustment truss rod may be high string height in the middle of the neck, or buzzing at the first few frets.

A guitar's neck is made of wood and is relatively flexible. When a set of strings is tuned to pitch it can put nearly 100lbs of tension on a neck and this will naturally cause a neck to pull upward due to string tension. It will look a little something like this:

The straight line in the picture represents the string, and you can see clearly how excessive bow in a neck can cause the string height to be too high in the middle of the neck.

To compensate for string tension a metal truss rod is installed lengthwise down the neck. There will also be a nut at the end of the rod that will be adjustable by using an Allen wrench or screwdriver. The compression of the adjustable nut against the rod causes the neck to bow backwards against the string tension thereby straightening a neck. A truss rod that is over-tightened will back-bow like this:

You can see the rise in the middle of the neck which will cause the notes behind it to fret out. A back-bow of any kind spells trouble and can easily be fixed by a qualified repair man.

Ideally we would want our neck to be as straight as possible while under string tension, or with a slight up-bow called "relief". Relief is measured in thousandths of an inch over the center of the neck. How much relief a person wants is a personal decision, but typically straighter necks are easier to play.

So take your favorite axe and look down the side of the neck. If you see either an inward or outward bow, you should probably have the guitar looked at by a pro. It's noteworthy too that when you change your string gauges the amount of tension on the neck will also change necessitating a truss rod adjustment.