Most new guitars arrive from the factory with the nut just barely playable. Older guitars may have the nut filed or worn down so much that fret buzz cannot be eliminated by neck or string height adjustment. If you have a new guitar, or you are replacing the nut with a new one, here is an alternative method to file and adjust the nut material to make your guitar play like the professionals guitars play.
Before adjusting anything, make sure your guitar is strung up correctly and that your neck is straight and not bowed or warped. If your neck is bowed you first need to adjust the truss rod. If your neck is warped it will require a more extensive repair. For the lowest possible action or to avoid fret buzz all across your finger board it may be necessary to have your frets leveled and crowned first.
You will need a set of nut files (available from Stewart MacDonald), and a good set of feeler gauges as well. Different grades of sandpaper are very useful too.
Fret each string individually, starting with the High E, between the second and third fret, use your feeler gauge to check the amount of space between the bottom of the string and the first fret. You should...