This file has two 37.5° angles and one 105° instead of the usual 45° angles found on regular triangular files. It is a standard Nicholson file available through machinist catalogs or large hardware stores. After examining the ends of frets on a number of instruments, I decided on a look I liked. I spent some time figuring out my technique for holding the file, and reduced the job to the simplest movements I could. I file the end of each fret in succession up and down the neck holding my hand and arm in the same position, hitting each fret end with a single stroke. I touch the very edge of the fingerboard with the safe corner edge of the file, slide over to the fret and push the file smoothly and firmly to avoid chatter marks.
My first cut is with the obtuse angle (105°) held level against the fingerboard, tipped down slightly, approaching the fret end at about 45°
The second cut is with the file rotated 90° cutting with the flat side vertical and acute angle down. I again attack the fret at 45° and roll the file a little as I cut the tiny little corner left by the first file stroke. By turning the instrument over to work the other fret ends, I routinely file the ends of all the frets in less than 2 minutes without rushing at all. It’s just a matter of 160 very similar strokes. Here's a view of the finished fret ends:
26. Level tops of frets by sanding. With my jack plane body and 600 grit waterproof silicon carbide paper, I sand the frets until I make a little flat stripe on each one. This is easier than it sounds. Using circular sanding motion, I avoid snagging the paper on the frets:
Here again, I support the neck broadly with my left hand, lifting the peghead off the bench, so I achieve a straight and flat fret surface. The drop-off over the body remains the same as I level the fret tops. While sanding I’m constantly checking the frets to see that each one is touched. I’m confident that if my sanding makes a little flat spot on each fret I have leveled them all very accurately. Usually one sheet of 600 grit is enough. It tears into two useful pieces for leveling frets, plus a handy narrow leftover strip. Here's the best shot I have of the top of a fret after leveling. I think you can see the flat strip on top, which extends across the full length of all the frets:
Speaking of sandpaper, I don’t economize on the waterproof stuff. I’ve found that 600 grit Klingspor waterproof paper from the Sanding Catalog is far more aggressive, cuts longer and loads less than 3M 400 grit. It costs more, but it’s well worth it!
27. Round tops and ends of frets. Backed by fingers only, I scrub 600 grit waterproof paper up and down the fingerboard bumping along over the fret tops and ends, rounding off the little flat stripes, and cleaning the file marks at the ends. I usually use the strips left over from tearing the pieces for my plane body sanding block. These are a bit over two inches wide and are just the right size for hand sanding.
28. Buff frets by hand, using Micro Mesh. Starting with 1500 grit, working up to 12,000 grit, I can polish the frets quickly and easily, sanding at about 45° across the fingerboard. With each successive grit, I reverse the angle so the sanding scratches cross each other. It takes only about ten seconds per grit to do the full sequence. For years I was too cheap to buy the Micro Mesh kit. I know better now. The small 3” x 3“ pieces I use for buffing frets will last me about 6 months.
29. Buff edges of fingerboard by hand with Micro Mesh. The same sequence of rubbing will polish the edges of the fingerboard and finish at the same time as I buff the frets, or I can use my buffer, and do it by machine. In most cases, the results are the same either way. On unbound fingerboards the filled ends of fret slots buff right along with the finish, and are hardly noticeable even on close inspection.
30. Clean up. The fret polishing drags particles into the fingerboard, so I clean with mineral spirits, and oil the board lightly with mineral or lemon oil to give it a fresh look. I hear of fingerboards being ruined by over-oiling, but I don’t think I’ve ever encountered one in my work. Generally, I suggest that oiling the board has only cosmetic value, and should be no more than an annual event, and lightly done at most.
31. Set up. Time to reassemble, restring, adjust action and check it out. If all went well, the finished product will pass inspection, and play better than new. If not, well, it’s time to fix it. I don’t try to level frets to correct neck problems, even at this stage. If there’s a hump at the body, difficulty with relief or straightness, I’d rather redo the entire job than try to fix it up. If I’ve kept my sense of time and rhythm, I’ll realize that I can afford to redo a job now and then. About once or twice a year, I grit my teeth and start over from scratch to make the job come out just right.