There have been several topics on cutting the slots in fingerboards. Here are the bits I use for this. Not only do they make a perfect fret slot, they stay sharp ( I used the same bit for about 15 or more rosewood board and it’s still cuts fine).
RPMs set around 18000
Feed rate 40 ipm
Depth of cut .010”
I use Fusion 360 for Cad/cam and project the slots onto the radius board so that while cutting, the slots are curved to match the radius of the fingerboard.
