So many of my regular readers (LOL) who play guitar have asked how to adjust the relief on a guitar neck. Since I am at that stage in my current guitar building project I thought it would be a good idea to provide some instruction...
Check your necks relief- Here is a simply way to check the relief in the neck if one doesn't have a straightedge handy... the instrument strung to pitch fret a string on the 1st fret and where the neck meets the body.
By fretting a string on 2 points we can then use the fretted string as a type of straightedge and get a visual as to how much relief is in the neck.
Measuring the gap between top of fret and bottom of string gives us an indication of how much relief is in the neck.
Now observe the space between the fretted string and the point of greatest relief...usually the 6th or 7th fret depending on the length of the neck. This gap can be measured with a feeler gauge if need be (you can place a capo on the first fret to free up one hand). If there is no gap, this is an indication that the neck is either dead flat or in a backward bow.
If the gap is substantial the truss rod may need to be tightened to reduce excess relief.
Determining the ideal relief The ideal relief for your instruments neck will depend on string gauge, playing style and the instrument itself. Light pickers, jazz musicians and the like may find .004/.006 gives the neck a very fast feel. The necks stiffness and willingness to flex can sometimes interfere with our desires though.
Those who have a moderate to heavy strum, like flappy extra light gauge strings, have a rounder f/b radius etc. may come to realize more relief (say .008-.012) may be necessary so that the strings can avoid buzzing.