Man, some of the methods here sound like a lot of work compared to what I use. lol
I use one of these very expensive $5.95 devices...........
Stick it in a 3/8" shaft collet, (I have similar mini-mill) move the spinning pointy end to the general top of smooth cylinder object to be drilled until it spins concentrically. I like to use the light reflections coming off the finder surface as an even more precise indicator than the two parts concentric spinning. And there you have just found a pretty-d accurate center.
I also use the heck out of this pointy end to find the center of a hole needing drilled. But you guys prolly already know this stuff.