For a more complex shape you can do it like an inlay, here's how. An inlay kit with an 1/8" bit was used for that, if you don't need to turn as tight you can use a common 1/4" bit with 1/2" and 1" O.D. bushings. But this will make a very snug fit, too tight for a sacrificial insert, if you have a belt sander it would be easy to take a little off the insert. Or choose 2 bushings with slightly less than 1/2" difference in OD, 3/4" and 3/8" for example.