Monday, February 1, 2010

Nut Compensation


Many of you have used an online "scale calculator" or "fret position" calculator to calculate fret positions to the ten thousandth of an inch, or with even higher (and still unattainable) precision.  You've marked out your fretboard with a dial caliper, you used a special luthier's fret saw and miter box.  You've spent all the money and time to achieve the highest level of precision.  And when you finally string up your instrument, it just doesn't work. What's the problem?

The nut isn't supposed to be located at the zero point of the scale!!!

There are many different adjustments that can be made that affect the playability of a string instrument- many more than I will treat here.  What I want to focus on is one of the most overlooked, but highly needed adjustments you will make. Nut compensation.

Why do I need compensation at the nut?

Imagine an open string. It is perfectly in tune.  You've intonated the guitar, which means you've performed some bridge compensation.  Now the twelfth fret is also in tune. However, when you press the string down at the first fret, you are stretching the string.  It has to get longer in order to contact the fret.

The harder you press, the sharper you get...

So, if you are in tune at zeroth (nut) and twelfth frets, you will be sharp at the first fret.

How do I correct for this?

The most common technique to deal with this is to move the nut closer to the bridge by shortening the distance to the first fret.  This is done independently of the scale length.  The question is, how do you know how far to move the nut?

Nut shaving technique

The answer is, I don't know how far to move the nut.  But, I've developed a technique that will work everytime.  I call it nut-shaving.  It goes something like this:

1) CUT IT SHORT- Before laying out your fretboard, deduct 0.050" from ALL measurements. If you use my fret calculator, located here, you can just add a column to calculate the new measurements. 

2) REDUCE CLEARANCE-  Now, you've cut your fret slots, shaped the fingerboard, glued it on the neck, etc. It's time to put strings on the instrument. Adjust string height at the bridge and at the nut.  Check the clearance at the first fret (see diagram below).  You want to start with 0.015" of clearance, or perhaps a little more, depending on your playing style, and slowly slot the nut deeper until you are comfortable.  Be careful! There is a fine line between perfect and buzzzzzzzzzz.  You are doing yourself a favor to make the clearance as low as possible.  Refer to the String Elongation drawing above to see why this is so.  If you reduce the clearance, the string doesn't stretch as much when you depress at the first fret.

3) SHAVE THE NUT- Tune it up, adjust the intonation (bridge compensation) and tune again. You should be in tune at the nut and at the twelfth frets.  Using a tuning fork, piano (one that's in tune) or preferably a strobe tuner, check the note at the first fret. IT SHOULD BE FLAT.  What we've done is we've shifted the entire fingerboard up the neck by 0.050".  Now, tape off the fretboard, and break out a small, flat file. Detune the string you are working on, and shift it out of the way. Remove material from the face of the nut, working back at an angle, until the string is in tune at the first fret.  Replace the string, retune. Continue to check that you are still in tune at the twelfth fret. Now check to see if you are still flat at the first fret.  If you become sharp, STOP!

4) Check the other frets.  You should now be "in tune" at every fret. Repeat for each string.  Refer to the diagram if you get stuck, and remember to have fun.

Nut shaving technique illustrated...


  1. This will help reduce my buzz, thanks!

  2. Nice illustrations!

    Your method of nut compensation is excellent for new construction. It's also good for upgrading existing guitars because it's easy to trim off .05" with a fine-tooth craft saw. Best to check intonation before doing this because the nut is already located forward on some guitars.

    I think it's important to add that, before nut compensation, the bridge saddle should be compensated to two fretted notes, usually fret 14 to fret 2; NOT to the open string. Steven Delft (google it) posted this in 1992, but it is still largely ignored.

  3. Thanks, Setitup. I'm glad you like my method. There is another benefit of this technique as well, this shape makes the nut far less likely to chip on the fretboard side, just under the string, the obtuse angle lowers the stress dramatically. As to your comment about bridge compensation, if you look at my description of the technique, I suggest intonating to the twelfth fret. This is a traditional method, since it is easy to compare the harmonic at the twelfth fret with the fretted note, no fancy equipment needed.
    However, the method you are citing is not possible. Before compensating the nut, you can only be "in tune" at two spots along the neck (maybe only one), but certainly not three. If you are in tune at the 2nd and 14th frets, you will NOT be in tune at the nut before you have performed nut compensation. This is possible to prove analytically.

    Thank you for your comments. I hope to share more techniques in the future.

  4. Right, after aligning the saddle with the fretboard, by adjusting for fret 14 in tune with fret 2, the open larger-cored strings will NOT be in tune, until you compensate the nut.

  5. Looks right but I don't see where Setitup Dan could be right about using this method on existing guitars.
    I'm not a luthier..just a pro with guitars that play out of tune. any ideas besides Earvana or Buzz Feiten?
    Or could you straighten me out on on what Setitip Dan is thinking?

  6. I think I've just understood what Dan is saying. He's tuning the guitar at the 2nd fret, then intonating at the 14th fret. He's not concerned about whether or not the open string is "in tune".
    Yes, you can do this. However, this is in no way better than tuning the open string and intonating at the 12th fret. In fact, you will get the same result, since the only thing you are setting in this step is the bridge position. As I said before, 12th fret intonation can be accomplished without a strobe if you have a good ear... so that's a plus over Dan's approach. I use the strobe.