A nut maker's guide

Your nut, together with your bridge, keeps the strings at a distance, both in terms of height above your fretboard and between each other. Because your string is fixed on the bridge and on the tuners, it will have to be able to move over your nut smoothly in order for you to be able to press your string on the key and produce a sound. When you press the string, you stretch it and that increases the tension. So, a nut has a lot to endure and must be made of a hard and smooth material. Natural materials such as bone and horn are very suitable and popular, but also composite, Tusq and metals such as aluminum are very suitable. Every material has a different hardness and density and will therefore transmit the vibrations in a different way.
There are also replacement nuts available where the nut slots are already filed, but since you still have to adjust them to fit on your instrument, we do not see the usefulness and we only offer blanks. For these pre-filed nuts, you can follow the same steps as below and skip the section for the distance of the slots and first cuts.

Clean nut rest
In most cases, your nut is placed at the top against your fretboard and at a straight angle from the neck. Sometimes the nut is placed in a gap in the fretboard or even at a slight angle. In all situations it is important that the nut has a flat surface to rest on and is set securely against the fretboard. It is the starting point of your scale! If the nut deviates, it affects the scale and can interfere with the intonation of your guitar.

With the gluing of your fretboard, a small amount of glue could have dripped out and in your nut rest. If there is glue residue it is necessary to remove it. Use fine sandpaper for this and stick it on a hard square block if necessary. Sand in one direction to avoid making curves. You can also use a fine file such as the Iwasaki tapered files or a micro chisel. These may be even more convenient as you can get into the corners more easily.

It may be useful to place a mirror on the other side of your nut rest so that can keep an eye on both sides and see if you are working straight.

Preparing your nut
First, we globally shape your nut:

Start with the thickness. Measure the depth of your nut slot and then sand your nut blank to the desired thickness. With natural material, the edges may differ slightly. In that case sand both sides. Use a caliper and measure regularly. If you have to remove a lot of material, start with grit 80 and from there on you work finer as you get closer to your desired thickness. It works best to glue a strip of sandpaper on a hard surface (mdf is fine) and to take your blank over it. Make sure you evenly sand and measure at several places of your blank to check this.

Then measure the width of your nut rest and draw this on your blank. Remove excess material with a file and then with sandpaper. Also regularly check if your blank fits well in the nut rest. Some prefer to tailor the sides later so that you have more room to move for positioning. However, since making the nut slots for the strings is a lot of work, I prefer to take the risk of screwing up my nut with shaping the outsides before making the nut slots. 

The top of your nut follows the radius of your fretboard and the height is determined by taking the height of your frets, adding the string distance and at least half a diameter of your thickest string. You need at least half a diameter width to hold the string in place.

It is easiest to work with feeler gauges because they are pliable and can follow the radius of your fretboard. Measure the height of your frets with the thickness gauge or caliper. The thickness gauges are in inches, so calculate the height to inches if your caliper is in mm (1mm = 0.03937 inches). Add the desired string height in relation to the first fret. You could take 0.03 "(0.762mm) as a guidance. Put together so many gauges until you reach this number. Place your nut in the rest and your selected thickness gauges against it, putting light pressure on the ends to follow the radius. Use a sharp pencil to mark the line of the top of the gauges on your nut. This will be your guide to the depth of your nut slots. Add half the diameter of your thickest string to your selected thickness gauges (or recompose to reach the required total) and mark a second line in the same way. This is the top line of your nut. Set your blank secure and remove material from the top, following the upper line. Start with a file and switch to sandpaper when you’re getting close. You can do the final finishing after filing the nut slots.

Measure nut slots
Determine how much space you want on the sides of your highest and lowest string. While playing, you do not want your string to slide off the fretboard, but too much space is at the expense of your string spacing. You could consider about 2.5 mm (0.1 ") from the side of the nut to the side of your string (not the middle of your string!). Draw this with a pencil on your nut for both sides 9bass & treble). Place your nut in the nut rest, set your highest and lowest string and place them on the marked position. Leave it that way, or slide until you are satisfied, mark the new spot and measure it.

If you would saw your string slots all at the same distance, dividing the remaining space of the nut to the number of strings, the space between the strings becomes smaller as the strings become thicker, or larger as they get thinner. That does not have to be a problem, but you can have much better playability when the string spacing (the gap between your strings) is equal. You calculate this as follows

Space to divide: Width of the nut – minus the space on the sides – minus the sum of the diameter of your strings.
Your string spacing: Divide this space by the number of gaps (number of strings – minus 1).

For your first nut slot (usually on the bass side): Add half the diameter of your string to the side space.
For the second string: Add half the diameter of the first string, half the diameter of the second string, add the side space and add the string spacing.
For the third string: Add the calculated number for the second sting to half the diameter of the second string and add the string spacing and half the diameter of the third string.
This way you calculate all positions. We have also created a nut slot calculator that calculates your input to the nut slot positions. That can save you a headache!

When you mark all the required string slot positions, also measure them from the other side to double check. It should be the width of your nut minus the calculated position.

Cutting nut slots
Secure your nut in a small vise for the beginning, with possibly some rubber in between to protect your nut. You can also place the nut directly into the nut rest and hold it in place with an assembled set of strings (at least two 2). For the first notch you can use a Feather edge file, the thinnest nut file or possibly even a very thin saw. You want to have a notch to help your file following the right line and not getting out of position. The nut is from a very hard and smooth material, remember, so it is slippery for your file. Make sure your notches follow the line of your strings so that the string tension is evenly distributed. 

Use your nut slot files with the correct thicknesses. The files have a different thickness on both sides so look carefully which side you use. File your slots slightly diagonally towards the head An angle of 6 to 12 degrees is sufficient, not smore than that. This ensures that the last point where your string touches the nut is on the side of your fretboard and the starting point of your scale.

Before you reach the right depth, it is sensible to place your nut in the nut rest and assemble the thickness gauges to the calculated height again for the height of the frets with the added string height. Slide them against your nut on your fretboard. Now you can carefully file your nut slots until your file just touches the gauges.

Nut slots finetuning
Now you can fine-tune your nut slots. Place all the strings and check the height of the first string on the first fret, the 12 fret and the lower fret. Set your neck in the optimum position by adjusting your truss rod and set your bridge saddles globally and feel how it plays. Finetune nut slot by nut slot if it still needs to be lowered. The thinnest strings are usually slightly lower than the thickest strings. For this piece of finetuning I prefer to use the files from the nut file polishing set and work quietly and patiently. A lot of in between checks are required, so it is string on, string off etc. At this stage you do not want to file too deeply by accident, because then you have to start again.

When you are satisfied, take your Feather edge file, your thinnest fret file or the thinnest file from the saddle and nut file polishing set and pull a thin and shallow slot in the middle of each nut slot. This helps to relieve any friction from the string.

Rounding it off
As your strings follow an angled, downward line from the headstock side of your nut, you need to round that side of your nut for the strings. Otherwise they can get hindered by the higher corners. Use a file to make a smooth rounded corner and sand it down till you are satisfied. 

Now you can neatly finish the top and sides and sand with fine sandpaper. Start lightly with 240 grit and then further in steps up to 800 or even 1200. Follow neatly the radius and use something soft under your sandpaper. Then polish with polisher and a soft cloth or grade 0000 steel wool. I’m always concerned that steel wool can discolor bone materials, so I would use steel wool only on darker colored material nuts and of course on aluminum. 

Gluing time
You can glue a nut with Titebond, but I prefer thick instant glue. With Titebond, use 2 or 3 small drops, put the nut in place, tighten your strings and slide your nut back to the right place. Wipe away any excess glue immediately. Let it cure for 24 hours. With thick instant glue, place 2 drops each on 1 / 3rd and 2 / 3rd of the nut slot close to the fretboard, place your nut in place and hold for 60 seconds with some pressure by hand.

Strings on and go !!