I fret dulcimers after the instrument is completely assembled. Some dulcimer makers fret the fingerboard before gluing it to the soundboard and have good results but I prefer to true up the fingerboard once I know the fretboard won’t move or warp during the construction process.
I use a long sanding block to sand the fingerboard dead level. The sanding block is a chunk of 2X4 that I planed flat and checked with a straight edge. There is 80 grit self sticking paper on the business side of the block. It levels the fingerboard very quickly.
A good straight edge is a wonderful tool. I use it not only for fretwork but also for making sure anything that should be straight and flat is indeed straight and flat. This includes planes, bench tops, shop made tools, etc.
I like to put a little relief in the fingerboard. The relief helps prevent buzzing when the action is a little on the low side. Most of the relief goes between the fourth and eight frets though it tapers a bit from there in both directions.
To put in the relief I make pencil marks in the area I want to relieve and sand those areas with a shorter sanding block. The sanding away of the pencil marks helps me target the right area. I use a small amount of relief as the instrument might end up with a bit more once the dulcimer is strung up and under tension.
Once the fingerboard has the proper relief I sand it with progressively finer grits of paper. Speaking of sandpaper, I should mention that I vacuum all the dust away after each step.
Though the fret slots are already cut I use a fretting saw with a depth stop to make sure they are still deep enough after the fingerboard has been sanded. The fret slots are just a hair deeper than the tang of the fret. The strips of wood laid across the soundboard are to help prevent the saw from accidentally cutting where it should not cut, like into the top of the dulcimer. This happened once many years ago. I don’t want it to happen again!
Frets are not intended to be a permanent part of an instrument. They eventually wear down and need to be replaced. The frets may also need to be replaced if the fingerboard warps and needs to be trued up.
I file a slight groove into the top of each fret slot with a triangular needle file. Should the frets need to be removed this slight relief of the edge of the slot will help avoid splintering the fingerboard.
At this point I check everything over and if all looks well I oil the fingerboard.
Next come the frets….