Guitar Neck - Measuring Neck Relief
Guitar Neck Measuring Neck Relief | Truss rod adjustment is covered in this minor guitar repair article.
Most of the time the truss rods are out of sight, quietly doing their job of keeping the necks of our guitars "in-line" and keeping the strings from buzzing. But why do we need to be concerned with guitar neck relief?
Changes in atmosphere, aging and drying of the wood in our guitars cause subtle changes that can greatly effect their playing qualities. What was once an easy-playing guitar and normal volumes in picking now has turned into a buzzing disaster.
So how do we know when it is necessary to straighten the guitar neck? The answer is we have to check the guitar neck relief and make the necessary truss rod adjustment.
Simply put, guitar neck relief is a very slight cupping or concave shape of your guitar neck. It is this cupping that allows for the elliptical string vibration of a picked or strummed string to clear the tops of the frets at roughly the mid point of the neck, or halfway between a fretted note and the bridge.
The amount of relief your guitar neck should have is Dependant on several factors:
Here is the procedure. Since a tight string makes for a perfect straightedge, we will use the string:
Here are some rough guidelines for proper neck relief:
If you find that there is no space between the top of the frets and the bottom of the string, the neck may be perfectly flat or may have a convex bow.
In this case you will have to loosen the tension on the guitar truss rod.
Quite often you will find that the best way to determine what the best relief for you is to find out how far out of tolerance you are by the above guidelines.
Then adjust your guitar from that starting point in small increments until you reach the optimum string relief for your guitar and playing style.
There are two different types of truss rods. One is called a compression rod and the other is called a bending rod.
Compression types of rods, were invented by The Gibson Co in the 1920's. These rod's work by securely anchoring one end of the truss rod, typically into portion of the neck that forms the heel, or around the 12th or 13th fret.
There is usually an washer and a hex nut placed on the adjustment side of the neck, which is most often found beneath a plate in the guitar head, right behind the nut.
This type of rod adjusts the neck by bending the neck outward (bowing) by applying tension, or inward (cupping), by loosening tension of the rod.
Remember that adjustments to the rod are made with the guitar "in-pitch" so that there is tension on the guitar neck and we can see immediate results.
These type of rods are usually placed very deeply in the neck (far beneath the fingerboard) and there is then a piece of wood covering the gap from the top of the rod to the bottom of the fingerboard.
Therefore when tension is placed on the neck the rod binds against the wood and forces the neck wood to bend upward or to bow and when you loosen the tension the rod tension is relieved and binds less on the wood resulting in the neck bow relieving.
Bending Rods work on a different principle that the Compression Rod. The rod is actually placed within a "U" shaped channel. The back end of the rod is secured to the channel and not allowed to move and the front end (adjustment end) has a washer and nut assembly, similar to the compression rod.
The Bending Rod is placed shallow in the neck, most likely directly beneath the fingerboard. The open part of the channel will face downward and the fingerboard covers the channel assembly. There is a film protection over the open part of the channel that prevents fingerboard glue from leaking into the channel.
When you tighten this type of rod the whole assembly moved in the direction of least resistance and that would be the open end of the channel, thus tightening the nut bows the neck upward. Loosening the nut has the opposite reaction.
One more to cover here and that is the Two-Way Adjustment Rod. It has a solid bar that runs parallel to the adjustment bar. The second bar is fixed and the adjustment bar or adjustment bar can be screwed inward or outward allowing for a great deal more adjustment in the guitar neck.
What this means is that you now have adjustment in tension and compression allowing more movement in the neck adjustment process. Most newer and high production guitars utilized this truss rod arrangement.
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