I would do as Tel said, i used to do a lot more intricate stuff about the size of the small hole ending around 7 thou thick.
Do each roundover in two halves and rotate as necessary. Above 7 mins polished up.
Hold on the protruding central lug so looking down the hole.
Grinding and sanding to size, you cant see what you are doing plus the tendency to grind on the .iss and generate friction, Yup gets hot quick with nothing coming off.