Things You'll Need:
- For this work you will need a small, fine, three-corner file to cut the notches and a larger flat file to dress the nut when you are finished.
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Step 1
First, a little analysis of the problem. When the guitar is set up with the gauge strings (light, medium, heavy, slinky, light top-heavy bottom, whatever…) and action (low, high…again, whatever…) that you need for your music, the string clearance from the nut over the FIRST fret should be the same as the clearance from the first fret over the SECOND fret when you fret the string at the first fret. In other words, you shouldn’t have to depress the string (which tightens a tiny bit, raising the pitch) farther on the first fret than other frets on the finger board. If the string tightens the same amount wherever it is fretted, then the intonation can easily be compensated at the bridge. Let’s get into the details.
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Step 2
Cutting deeper notches in the nut is one of those things that can’t be easily undone so let’s be careful here. A magnifying glass is handy to really see the string notch and to examine the fret clearance as you fret the string. Take a really good look at the nut under good illumination. Fret the string at the first fret and at the second fret and at other frets up and down the neck. You can see how much clearance the string has by observing the shadow as you depress the string. You may pick up some discrepancies. That would indicate that the neck relief needs to be adjusted. If so, see my article “How to Correctly Adjust the Truss Rod in Your Guitar Neck”.
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Step 3
If everything looks OK, carefully lift the first string (the little one) out of the nut and over the side of the neck. Don’t detune the string. We need to keep it at the right tension as we work on the slot. You will want to tune it back up to pitch every time you put it back in the slot to check what you’ve done. Look at the empty notch carefully. See the angle that it takes toward the machine head? You don’t want to change that angle unless you have a good reason and know what you are trying to accomplish.
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Step 4
The slots were probably cut with special files that were about the same size as the strings. In my opinion, it is better to establish a notch just deep enough to hold the string in place. The thickness of the string is enough. I prefer to have the string resting on the sides of a triangular notch because I think that minimal bearing surface (in good hard nut material like bone or brass) provides the least friction. That in turn makes the guitar tune better because it does not prevent the string tension from distributing itself equally along the entire string when you adjust the tuning peg.
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Step 5
With your three corner file, take two or three gentle strokes toward the tuning peg. Now examine it again. I want you to get a really good feel for how much material you are removing. I want you to see how it feels to file at the correct angle. If the nut has deep slots, you will be removing a lot of material from the sides before you ever get to the bottom where the string rests. If you think you will hit the headstock with the end of the file, you can protect it with some masking tape.
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Step 6
The basic rule here is DON’T TRY TO GO FAST! Two or three cutting strokes at a time are plenty until you have a good feel for this. After every few strokes, put the string back in its notch, tune it to pitch and fret it. Carefully look at the clearance you are obtaining. The trick here is to always stop before you take one stroke too many with the file. Do this with all six strings while keeping the guitar up to pitch and pretty much in tune the whole way. On the big strings, you may want to rock the file in the bottom a tiny bit to widen the notch. With a very good file it’s possible to cut the bottom of the notch deeper than you would like before obtaining the correct width for the larger string. Better to keep the notch a little wider and flat in the bottom.
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Step 7
When the notches are correct, use a flat file to remove the excess material sticking up between the strings. Nothing special here, just make it look pretty and don’t let the file nick anything.
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Step 8
That’s all there is to it. If you accidentally go too far, it’s not the end of the world. You will have to shim the nut with a piece of card stock underneath. That requires getting the nut out. Be careful not to cause damage to the end of the fingerboard. The nut can usually be removed by tapping gently to break the glue bond.
