I have a design regarding slotting of keyways parallel to the axis of the piece. Primarily developed for slotting internal keyways in piping annulus, the piece makes use of a "wolley tooth waggler" as the British would call it, simple dial gauge deflection by everyone else in the world.
The design is not "simple" per say but references components from an assembly drawing. It may not be what you are looking for, slitting is different.
The design is not shareware, you can contact the company none-the-less.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada