I'm making a hand-held tarp grommet setting tool I can use on a ladder, with dies that screw together. I can grind the shank end of a drill bit into a radius form tool and hold it tilted forward but it won't cut very deep before the shank rubs, although the resulting shallow ellipse is likely good enough for this job, I'll find out how well it flares, rolls and crimps the tubular rivet when the tool is complete. If it doesn't work I know a guy who can modify this kind of stuff until it does.
Drill shank cutters work better on round pulley grooves for wire cable than for cuts into the flat end of the bar.
Is there some simple geometric way to grind an accurately circular convex radius lathe bit that I may have missed? Concave radius forming bits are easy to shape with a tapered Dremel stone marked at the intended size. The taper provides clearance so the bit can be clamped flat to cut a true circular arc.
A General drill bit grinding fixture might be the right sort of tool if it could clamp the lathe bit flat and was sufficiently rigid. I can't really justify the cost of a new punch grinding fixture and haven't found a used one.
--jsw