Hi, join the club, I built a cheapo cnc router and added a fourth axis "A axis" and have been trying to find the same answer for some time now, that this makes me very interested, I have tried drawing the normal X Y profile in cambam and setting the stock thickness to the intended radius the Y axis is the intended diameter and offset by the radius and creating Gcode to profile the design the full thickness of the stock with fairly deep increment cuts. I loaded the Gcode into Mach3, set the zero for X axis start (0), Set the centre of the spindle for Y axis start (0) and set Z zero on the surface of the stock. If you are turning from square stock you must remember to set the Z clearance level higher than half the diagonal measurement of the stock. I used a standard half inch worktop cutter and manages to do a reasonable sweeping profile which polished up nicely with the old glass paper.
I must point out I am a complete novice and pensioner playing at this as a hobby but try this on timber as I know it works