Types of Truss Rods
Source: Guitar Neck Repairs
Types of Truss Rods:
There are two main types of truss rods used in contemporary guitar construction. The one way truss rod and the two way truss rod.
How the One-Way Rod Works:
The tension rod works in a similar manner to the guitar strings. The strings try to pull the neck forward by putting tension on the wood of the guitar neck. The tension rod does the same thing by putting tension on the wood of the guitar neck in the opposite direction, thus counter-acting the string tension.
This method of counter-acting the string tension is greatly enhanced the deeper in the neck the rod is buried. That is why in straight rod installations you will usually see the rod get deeper as you approach the heel of the guitar because the neck gets progressively thicker as you approach the guitar body.
What is unfortunate about the one-way Truss Rod is that you have the ability to tighten the rod and introduce a counteraction to the string tension, but if the opposite conditions exists in the neck you cannot adjust for that.
How the Two-Way Rod Works:
The Two Way Truss Rod consists of two rods. One on top of the other. The are welded or are mechanically fastened together at the end opposite of the adjustment nut.
The Two Way Rod operates identically to the One Way Rod in that it depends of tension to bow the neck upward. The great thing about the Two-Way Rod is you can also loosen the tension an even apply some tension in the opposite direction, thus introducing backward bow to the neck.
This can save major repair bills and save you from fingerboard removal, shaving down necks, shaving fretboards and a number of other ills.
Methods of Truss Rod Installation:
There are many theories as to how best install the rods. Certain manufacturers are proponents of just laying a straight rod into the neck. A more common practice is to lay the rod in the neck with a gradual curve – usually at the body end of the neck. Both of these methods depend on the neck being straightened by applying tension to the end of the rod.
I favor the curved rod installation even though it is a more difficult repair to make. The curve allows much more counter-action to string action to be dialed into the truss rod.
How Much Curvature:
When installing a new Truss Rod, I keep the two ends of the rod fairly shallow – usually about
1/8″ below the surface of the top of the neck. This can vary depending on the thickness of the neck. Do not allow the channel to come any closer than about 1/8″ from the bottom of the neck.
The curvature should be set so that the center of the rod will be about 3/16″ to 1/4″ deeper than the rod ends. Of course you should always measure all of the depths that you have to work with to eliminate the risk of routing through the neck wood.
Tags: Guitar Neck Repairs, guitar repair, guitar truss rod, how to adjust a truss rod, types of truss rods
