How to Measure Guitar Neck Relief

How to Measure Guitar Neck Relief

First of all lets get the basics out of the way. Most acoustic guitars have an adjustable truss rod that runs down the length of the neck. The rod is seated within a channel that is routed down the center of the neck, and in most case is laid loosely with attachement only at the end opposite the adjustment end.

These truss rods come in 3 basic varieties:

Fixed:

The fixed truss rod can be a cross-section of steel, aluminum or even hardwood (hardwood is used mostly in classical guitar construction). The steel configuration can be tubular, a steel tee or steel bar stock. Aluminum is usually heat tempered aluminum and is configured as bar stock.

One Way Truss Rod:

A one way truss rod allows tightening of the rod to bow the neck upward. You cannot bow the neck downward with a one-way rod.

Two Way Truss Rod:

A two way truss rod is the best of both worlds. Tightening the rod bows the neck up, loosening the rod bows the neck downward. So you can basically correct any neck condition with the exception of a twisted neck.

Neck Relief:

You will see this term used in the guitar community and it refers to the amount of bow that a neck exhibits. The terms used to describe neck relief are very confusing. There is forward bow and backward bow.

Forward Bow:

First of all this is what you want in your guitar neck. At least a little bit of it. To help you visualize this just think of forward bow as a slight ‘cupping’ of the neck. In other words if you held a string from the first fret to the 12th fret and held the string tight against the frets on both ends, the center of the neck or the 6th fret would be slightly above the fret or would clear the fret.

Backward Bow:

You don’t want this – not at all! If you have backward bow, you will have to have the strings on the guitar higher than usual to keep them from buzzing. This is where an adjustable truss rod is worth its’ weight in gold. If you do the same exercise as above, with the guitar string, you will find that not only does the string contact the center fret, it actually curves over the neck.

Measuring Neck Relief:

There is, of course a magic number that we want to shoot for with neck relief for our acoustic instruments. Firs of all, place a capo just behind the first fret and tighten it up. Don’t over-tighten as this may cause the string to rise slightly. Now press the string down at the 12th fret.

Next take a feeler gage and measure the distance between the 6th fret crown and the bottom of the first string. The measurement should be between 0.010″ and 0.015″. If you find that you have slightly more than this, do not worry too much about it, unless it is excessive. If you have less than 0.010″ consider a truss rod adjustment to get your neck relief within tolarence.

Precautions:

Proper neck relief occurs between the nut and the Middle of the neck. If you have relief (Forward Bow) between the middle of the neck and the body or if there is a hump in the fingerboard where it meets the body, or over the top plate of the guitar – that can mean problems.

Adjusting for Proper Neck Relief:

This issue will be dealt with in our article on How to Adjust a Guitar Truss Rod.