Flat Fretboard Form (e.g. Dulcimers)
Make sure the fret slot is wide enough. If too thin, widen a little with back saw. The fret should stand up in the slot but not sit in all the way down. It should not need to be supported during fretting. Fill the slot with wood glue, then place the fret in, and bang it in with the fretting hammer. There should be some squeeze out – wipe this away. Do not trim until the glue has completely dried.
The glue is to seat the fret well. It fills in any gaps and makes the wood swell up around the fret, seating it in well. Contrary to what some dulcimer builders think, this is a good idea – they think that the glue makes it impossible to remove the frets if they need to be. Actually, it makes it easier – just iron the frets, the glue absorbs it’s self into the wood and the frets can be removed easily.