This is the fourth in the series of the Guitar Nut. If you have not read the first 3 articles, please read them to become familiarized with materials and initial shaping techniques that are required.
Tools and Materials:
Wooden Graphite Pencil
Stationary Belt Sander
6″ 4-Way Shoe Rasp File
Adhesive Sandpaper 120 Grit
Adhesive Sandpaper 220 Grit
Silicone Carbide Sandpaper
#0000 Steel Wool
Woodworkers Marking Knife
With the guitar nut cut to length and fit exactly into the nut channel as described in the article above, Fitting the Guitar Nut, it is time to rough cut the nut to proper height.
There are 2 ways that you can use to roughly shape the guitar nut to proper height.
Method 1: This is a method that I have used for years and works quite nicely. Take a wooden graphite pencil, about 4 to 6 inches long cut off the metal eraser end and sand it exactly in half lengthwise. The point should be sharpened prior to sanding the pencil.
While holding the pencil parallel with the fretboard, with the flat side down, and on the first 3 or 4 frets or so, trace a line on the backside of the nut. This will represent the depth that the string slots should be made, similar in height to a zero fret installation. (zero fret fretboards have a fret installed just ahead of the nut and are actually supported on this fret.).
For the finished nut height you should add about 0.030″ to the top of this line for the nut to cradle the strings. You will want about 50% of the bass string set into the nut and the treble string set in their full depth and then some, because of the small gage of wire.
Method 2: If you know the crown height of your frets, for instance typical frets are around 0.040″. You should add about 0.30″ to that then and stack feeler gages to that height or about 0.070″. Lay the feeler gage up against the nut and press it so it follows the curvature of the fretboard (if there is one). Take a sharp pencil or a Marking Knife and trace along the top of the feeler gage.
Next with the nut still in place mark the top of the nut to angle the same as the guitar headpiece. Mark this slope of each side of the nut. Connect these 2 lines on the front of the nut once it is free from the nut channel.
Once the nut height has been marked, you can take a plastic hammer and and a wood block and knock the nut loose with a small top – that is if you glued in the nut.
Now put the nut in a machinist’s vice and take a mill file or sanding sticks and cut down the nut to within a fraction of your lines. Make sure you are following the contour of the fretboard on the front and back of the nut.
Some luthiers prefer to have the nut curve downward toward the headpiece of the guitar. This will give you better string to nut contact because you need not worry as much about the string contact the very backside of the nut for support. This distance is greatly reduced with this shape of a nut.
Finish Sand The Nut:
Now take some 220 Garnet sandpaper and smooth the nut. Next take 400 Garnet or Silicone Carbide sandpaper and smooth it even more. Your next step will be to polish the nut with #0000 steel wool. By now the nut will take on a nice polished look and you are ready for the final step of cutting in the Perfect String Channels.