It surprised me how much goes in to this little thing. On cheap instruments, they're moulded plastic. These are bone, like the saddle. Because of bone's density it transfers the energy of the strings better to the soundbaord.
Having first set its face side, face edge and length with a sanding board to fit it's slot on the neck, I mark the curvature of the neck. For this I use the trick, which I think I've mentioned before of half a pencil along the the frets, and sliding across them to mark the nut.
(Half a pencil lengthways, half sanded off on a belt sander of planed off.)
That line represents the height of the frets, so the bottoms of the slots for the strings must not go below or even touch that line, or the string will buzz, vibrating against a fret.
I have a little card with string spacings on for different nut widths. Mine is 42mm, in blue.
I pencil where the string slots should be.
Although it's not absolutely necessary, it would ne nice if the top of the nut were the radius as the fretboard.
So I sand the radius using a fretboard sanding block with the same radius.
I also shaped the top of the nut back the same angle as the headstock, giving the strings a straight run to their posts.
Looks OK, but those shoulders are square and sharp.
So I rounded them over.
I then used a ruler to mark the lateral angle the strings will go across the nut in a straight line to their posts.
I invested in some special files to create the slots. Although they are each a specific size, I can make each slot a little wider if need be.
It looks relatively easy, but experience has taught me to have a stock of bone blanks.
