In the photograph above are some of the tools I use when filing frets after they are installed on a dulcimer.
On this dulcimer the ends of the frets have already been filed flush with the sides of the fingerboard. The next step is to assure there are no high or low frets as these are one of the causes of buzzing and other annoyances.
I draw a line along the top of the frets with a marker and lightly file the tops with the flat, fine diamond sharpening stone. When the lines from the marker are gone I know the tops of all the frets are level.
I choose the color of the marker based on the dulcimer’s aura. This one needed blue. Only kidding. Or am I?
The tops of frets need to be round and define a singular point of contact when the string is pressed down behind it. I mark this point by again drawing a line with the marker along the crowns of the frets. I use the triangular file to file the sides of each fret so it slopes towards the line until there is barely a hint of the line left. The corners of the file have had the teeth ground off to help avoid gouging the fingerboard. The metal shield placed around the fret I am working on also helps.
The small metal square is one of several in different sizes I use as straight edges to assure the tops of the frets are still level as work progresses.
The block of wood with a file embedded in it at an angle is used to bevel the ends of the frets. The small, skinny file with the orange handle is used to deburr the corners of the frets at the edge of the fingerboard. The same file is use to round the end of the frets. Skipping this step usually results in blood loss for the player; the ends of the frets become sharp after filing.
After completing all the above the crowns of the frets are further rounded and polished with fine sandpaper, steel wool, and then buffed until they shine.