Sanding Down the Top the Nut
As a general rule, the top of the nut should be sanded down so that half of each string’s diameter sits above the nut. When strings sit too deeply in the nut, they tend to creak during tuning and can break more easily. Sympathetic buzzing is also a common symptom of strings sitting too low in the nut.
Sanding Down the Bottom of The Nut
When sanding down the bottom of a guitar nut, the most important thing is to be able to sand slowly, on an even surface and check the nut often, taking care not to remove too much material.
The image above shows a guitar nut in which the strings are submerged too deeply.
Cross section of a guitar nut and strings. You can see that the strings are sitting too deeply in the nut.
The image above illustrates how much material will need to be removed from the top of the nut so that only half of the diameter of each string sits above the nut.
Process for Sanding a Nut Down*:
The process below is the same for sanding down the top, or bottom, of a guitar nut.
1. Loosen your guitar strings and then move them to the sides of the nut. DO NOT cut or completely remove the guitar strings! (You’ll want to be able to replace the nut and put the strings back in the nut slots to check your sanding job.)
2. Remove the nut.
3. Draw a line (or Not)
(In general, sanding down a nut involves removing tiny amounts of material, so measurements and drawing lines usually aren’t necessary. More often than not, getting a nut to the right height is a matter of trial and error. Of course, if your nut needs 1mm, or 1/64 in., or more, material taken off, then drawing a line as a guide is recommended.)
4. Using a sanding block, sand the bottom (or top) of the nut until that the nut sits at the desired height.
5. Replace the nut, tune the strings back to pitch and use a feeler gauge to determine whether the nut has been sanded down enough. (If you were sanding the top of the nut, then check to make sure that half the diameter of each string is now sitting above the nut).
6. If your strings are still too high or still sit to deep in the nut, or both, then repeat steps 1 through 5 until your strings are at the correct heights.
(We used video footage and 3D computer animation to illustrate this concept in Fret MD: Acoustic Guitar Setup and Maintenance.)
If, after sanding your nut down, some strings are now too low, find out how to shim up your nut.
* This process is the same for all guitars with a bone, plastic or graphite nut. (e.g. Electric guitars, acoustic guitars, basses etc.)