If you can make flat-bottomed holes in about the right place and size (20 +1/-0 mm) then that satisfies this project. I can't make flat-bottomed holes.
I use my endmills to make flat bottom holes (when I had a drill press) but have only up to 1/2" at the moment. With the lathe, I can only drill a hole dead center. A mill would do it with ease - but I don't have one quite yet. I can make the finned disk and you could take over from there.