Truss Rod Router Bits
All modern electric and acoustic guitars have truss rods inlayed in their necks. Truss rods were developed over 60 years ago to help reinforce guitar necks and keep them straight. Over time due to environmental conditions, guitar necks can warp or bow. The truss rod helps correct this natural tendency. Basically it's a rod that is inlayed down the center of the guitar neck. When pressure is applied to the truss rod, tightening the truss rod, the truss rod bends inside the neck forcing the neck to bend with it. Loosening or tightening the truss rod will bend the neck in the proper direction to keep it straight. Generally speaking, the straighter the neck the more comfortable the guitar is to play.
Truss rods come in all different shapes and sizes, so do their access points. They have all different types of ends. The most common ends can be adjusted with screwdrivers, allen wrenches, and nut drivers. Some truss rods can be access through the truss where the fretboard ends. Others can be accessed at the bottom of the neck where the neck and body meet. Still other odd truss rods must be accessed through a back panel on the back of the guitar.
That is why there is no all-purpose truss rod adjustment tool. You will need a kit of truss rod tools if you plan on adjust many different guitars. Occasionally, or should I say rarely, you may run into a guitar that has a broken truss rod. This rarely happens unless the guitar was really abused of poorly repaired / set up. Most broken truss rods are not really worth fixing because of the cost of the repair. Many truss rods are glued in the neck in such a way that you have to remove the fretboard and cut out the truss rod. Needless to say, it is a time consuming repair. Also, most quality guitars don't have this problem. It's the cheap guitars that usually need this repair. Replacing a truss rod in a cheap guitar is not worth. You might as well just buy a new guitar. In the unlikely event that you actually want to take the time and incur the cost of replacing a truss rod, you may need a router bit to clean out the truss rod slot. A ¼" shank, spiral down cut router bit will work fine. Truss rods are sometimes glued in place with a shim board under the fretboad. This helps prevent the truss rod from damaging the fretboard. It also can put glue in the truss rod slot. Once the truss rod is removed, measure the slot size needed for your new truss rod and pick the appropriate sized bit. Set up a jig that allows you to cut a straight line and go for it. The router bit will clean and widen the slot for the new truss rod.
As I said above, this is a rare repair for most repairmen. I think this tool is more accurately categorized as a guitar building tool—not a guitar repair tool. I figured that I would add it in this section because it is repair tool that is sometimes used. All that being said, I don't think this is a guitar repair tools that you need to have or will use all the time. It is a great guitar building tools. If you build guitars, you should think about buying a whole set of router bits. As far as guitar repairs go, I think you could probably live without one initially. If you would like more information about how to adjust your guitar truss rod, please see my how to straighten your guitar truss rod article.