This task may, at first glance seem like a simple one, but the importance the nut plays in the guitar tone and the precision that is needed in the construction of the nut should not be taken too lightly.
Tools and Materials:
Wood Chisel Set
Incra Steel ruler
Adhesive Sandpaper 80 Grit
Adhesive Sandpaper 120 Grit
Adhesive Sandpaper 220 Grit
Xacto Razor Saw
Preparing the Nut Channel:
Prior to making and fitting your guitar nut, you should make sure you have completed the following steps:
1. The fretboard is glued in place and the neck has been shaped and sanded.
2. The frets have been installed and finished.
3. The nut slot is finished and has a clean bottom joint and the channels is of consistent width.
4. The face of the headstock veneer (if there is one) is parallel to the face of the fretboard endgrain.
Rough Sand The Nut Width:
The very first step for fitting the nut is to size the nut to perfectly fit the nut channel you have provided.
Set up several sanding surfaces with the following grits of Self-Stick Sandpaper. I start out with Adhesive Sandpaper 80 Grit
to hog a lot of material off the nut, use Adhesive Sandpaper 120 Grit
to fine tune the thickness and finish with Adhesive Sandpaper 220 Grit
The sanding surfaces should be made from a scrap slab of granite or marble countertop. You can pick up samples or small scraps and cutt-offs from kitchen and bath home centers for this.
Place the nut on its side and carefully sand the nut on the 80 grit paper. This works best if you hold the nut between your thumb and index finger, on the ends of the nut. Apply even pressure while doing this. I often press in the center of the nut with my other hand to try to even the sanding procedure and to take off additional material.
Carefully check your progress with the Vernier Calipers and make adjustments as necessary. When you approach your target thickness, check the nut in the channel. Switch over to the 120 sanding surface until you get a snug fit. Note that you should not need to force the nut into the channel, nor should there be any play in the nut joint. It should slip in the joint and not rattle around.
Check The Nut Bottom Joint:
If you constructed your neck properly, the bottom of the nut channel should be square with the sides of the channel. If not, and the bottom of the channel is angled, you have two options:
A. You can angle the bottom of the nut to match the angle of the nut channel.
B. You can square off the bottom of the nut channel and have the nut extend downward below the bottom surface of the fretboard. (Note that some guitars are constructed this way).
To cut this joint down you will need to use very narrow chisels. You also will need a file with cutting teeth on the edge of the file. There are also some specialty nut seating files that are available for this tedious job. One final method would be to make a cutting jig for a Dremel Moto Tool to accurately cutting this slot. (That is the best option in my opinion.)
Cutting the Nut To Length:
Set the nut securely into the nut channel. Take a very sharp pencil or a marking knife, and strike 4 lines on the nut, on each side of the fretboard and each side of the headpiece. This is to compensate for any angle that there is between the fretboard and the start of the headpiece.
Rough cut the nut to length with an Xacto Razor Saw. Be sure to leave some extra material beyond your lines to sand down to.
Now take a sanding stick with Adhesive Sandpaper 120 Grit adhered to it. I like to use a small stick, about 1/2″ wide so I can see my progress. Clamp the nut in a vice with one end sticking up. Carefully sand up to your lines that you scribed on the nut. Flip the nut and do the same with the other side of the nut.
Check the nut fit. Ideally, the nut will extend just a whisker beyond the edges of the fretboard.
Also at this stage of construction, I’m assuming that the neck does not have the finish applied to it yet, so you can finally sand the nut length safely with the nut installed in the nut channel. Because the ends of the nut are usually at an angle or slightly curved because of the transitional shape of the guitar from the neck to the peghead, I use a sanding surface with a radius bottom.
It is best if this radius matches the radius of the transitional curve. Do this with 220 grit self-stick sandpaper, until you have a perfect joint.
GLS Tip #1: If the nut does not quite fit tight enough to complete this sanding operation, just put a dab of Duco Cement on the nut to hold it against the endgrain of the the fretboard. You could also use Titebond glue. Take care not to use too much as you will have trouble getting the nut back off. Just a little dab will do ya.