Evaluation of relief and neck adjustment in electric and acoustic guitars.

In this article you will find technical information and practical tips about the adjustment of the guitar neck truss-rod.

It is advisable you have read and understood the article about necks and truss-rods What is the truss-rod? also published on this blog.

From top to bottom: convex, straight and concave neck.

Neck adjustment: checking the relief

Assuming for sure that you have read the above mentioned article What is the truss-rod? where neck and truss-rod typologies are described, let's see in practice.

Let's assume we have been owning the guitar that has to be set since some time; that the guitar is equipped with our usual gauge string set and it has a good general setup that allows us to play. This also applies to a new instrument we were able to personally test before purchase or an online bought instrument that features builder's or retailer's warranty of a good factory setup.

As the first step, we have to verify if the neck is straight enough. Let's press our left index on the low E string at the first fret after the nut, and the right little finger on the first fret out of the guitar body, usually the 16th or 17th on electric guitars, 14th or 12th on acoustic ones. We are practically using the E string as a rule between due frets far from each other on the fretboard. Let's hold steady the string pressing fingers and use the right index or thumb to try out the distance between the string and the frets top, called relief, in the neck portion around the 7th-8th fret. We can repeat this operation for smaller portions, moving the pressed points to look at limited parts of the neck.

If we push the right index at the center of the observed string portion, we will feel it tapping slightly on the frets, by example between the 5th and the 9th ones; so we will be able to evaluate if the neck in that area is straight or bowed, in the sense of concave. In case the neck is convex, that is backwards curved, we will not feel the string hitting the frets, but most likely resting on all or almost the frets we are observing. Actually, in case the neck is convex, we should be able to notice the flaw without doing any test at all. We should have suffered problems just playing the guitar, such as fretboard buzzing, lack of intonation , even blockage of strings on frets. In these extreme cases it is advisable to turn to our trusted luthier, though we have read in the article What is the truss-rod? that double action truss-rods can fix backwards bowed necks too.

A second step you can do – but this requests a trained eye and experience – is observing the neck as if you were pointing a gun, both from the headstock to base and the contrary. If warping is considerable, you will see the fret line not following a straight line , instead bowing in one way or another under the strings. Sometimes the bend can be unpleasantly irregular and affect just a portion of the neck or just one side, in this case indicating a suspected longitudinal twist: bad business indeed, and you'll have to turn to your trusted luthier.

Are there reliable specs?

We could start now a gigantic series of considerations and suggest several rules about the height we should feel between the low E string and the top of the frets. Every manufacturer has its measures, or specifications, described in the specialized literature for every guitar and variable according to models and lines of instruments, sometimes according to production period too. Decades ago Fender or Gibson specs could be stricter than what the same companies claim today for similar instruments and replicas made with more economic criteria.

If we move on to luthiers, a skilled craftsman usually has his own stricter specs, tailored on the basis of his ability in guitar making and customer requests.

Just to give you few numbers, Strat and Telly manufacturer specifies a variable relief of 0,3 to 0,25 mm according to the fretboard radius (7”1/4 or 9”1/2), measured at the 8th fret with the low E string pressed as above described.

The importance of an excellent fretboard

By and large, the higher the grade of an instrument, the more precise should be its fretboard finishing . Computer controlled machines are often used today (CNC: Computerized Numerical Control ), thus permitting to get nearly perfect fretboards in a few minutes, according to machinery accuracy and software refinement. When instruments are built by thousands per month, time has its importance and cost, but new construction techniques give life to better and better guitars in the budget range too.

Before giving some general tips, you'd better know that a low height of strings over the fretboard does not depend on the truss-rod and our adjustment capability only, but mostly on frets placement and finishing. When a neck is set very straight with very low strings, it is not rare that buzzing becomes noticeable because of not perfectly layed and finished frets. In these cases it is advisable to get back to a state that the instrument can accept or turn to a luthier and get an intervention of no small account called dressing.

That is not all: in fact neck setting is only a part of the more articulated adjustment of guitar action. This operation also involve working on the bridge, the saddles and eventually the nut. We are back to this topic in a specific article also issued on the Soundsation blog. So far, let's just make our guitar neck reasonably straight .

Straight neck, OK; but how much straight?

Some experienced luthiers think that the neck must be perfectly straight, or almost perfectly straight. Consequently the distance (relief) of the string pressed by the right index and the middle frets of the neck should be near to zero , almost imperceptible. Between ourselves, sometimes luthiers state that to show us how good they are... Anyway this is possible only if the fretboard is perfect and all the above mentioned action adjustments have been done professionally.

Remember that this article only purpose is the adjustment of the relative straightness of the neck, not getting a perfect instrument. When you make your personal setup, refer to the suggested specifications on handbooks and manufacturers' websites, Please consider that:

• a straighter neck, with minimum relief, makes comping, jazz and virtuoso rock solos, chord melody easier to play; moreover, our fingertips pressure will be light and will not cause subtly out of tune notes
• a neck with a certain relief, therefore slightly curved, makes easier to play rock and blues classic techniques, as the bending. Strings vibrate more freely and the instrument sound will be somewhat better. A higher fingertips pressure is needed to press the strings, possibly generating few hertz dissonance in played notes.

It's time to adjust the truss-rod!

So many premises just to arrive at a simple operation: turning clockwise or anti-clockwise the moving nut of the truss-rod! Once the straightness has been verified, if the relief is too pronounced and the neck appears too concave, tighten the truss-rod turning the nut or the rod head clockwise, as if it were a screw. If the relief is poor and the neck seems too straight or even convexity prone, loosen the truss-rod turning it anti-clockwise.

If you are working on a vintage Stratocaster style guitar with truss-rod access at the neck base, you must in the order: completely loosen the strings, undo the heel screws and lift the neck, adjust the truss-rod guessing the resulting effect, reassemble the neck and tune the strings. In case it is needed, you have to loosen, unscrew, lift, adjust and reassemble again: good luck! (Leo Fender did not like the idea that musicians adjusted themselves the neck). Experience or a luthier's work will help not to repeat this operation too many times.

Once the adjustment has been done, if you look at the neck from the headstock towards the base, you will see it magically adapting to our corrections. In case, it is possible to help a little by means of a slight pressure of the hands in the adjusting sense. Attention, most times little adjustments of one quarter of turn or less are enough. Always start from a slight opposite rotation before going on in the desired direction.

The described process applies to both electric guitars and acoustic guitars, to adjusting access points at the neck base and behind the nut. And to electric basses as well!

Attention: if the truss-rod is blocked or hard to adjust, do not pick it! Stop instead and turn to the luthier's help.

Once you have checked the effects of the adjustment from the neck ends, press again the low E string with your fingers pushing at the first fret and last fret out of the body. Then play as usual what you usually like, and try to understand if things are better or worse from a performance point of view. Check if there are no buzzes, if bendings are not hampered, if the sound is solid and the sustain is adequate.

The truss-rod adjustment has to be made by trial and error, until you get an acceptable result. You can further verify string height compliance to manufacturer specs using a caliper or a feeler gauge , but always remember that neck adjustment is not the only needed operation. Also remember that your trusted luthier is always ready to welcome you if you don't get over it. After having read this article, you will better understand what he is going to do to your guitar.

In this article we have dealt with the truss-rod adjustment, a key step on the way to guitar general action adjustment . We talk about this topic in an appropriate article you can find on the Soundsation blog!

Fabrizio Dadò

References
Dan Erlewine: Guitar Player Repair Guide, 2^nd Edition (Miller Freeman Books, 1994)