I once ran a few thousand wooden bobbins (used for tapestry weaving) and some crank handles, on a South Bend lathe, modified with a shop built tracer attachment.
The nut was removed from the cross slide so it could move freely. A follower pin was mounted on the back of the cross slide and a long tension spring attached between front of the slide and the back of the saddle. An armature was mounted to the back of the bed that held template (cut from ⅛" flat stock) so that it would engage the pin. Thus, as the saddle was moved along the Z axis the pin would follow the template, and the slide move accordingly. Depth of cut was adjusted by the compound slide (set perpendicular to Z) and the tool was ground with a bullnose radius same diameter as the pin. The arrangement worked well. I do have pictures somewhere but that was back in the film days...