I love my self-centering vise. To center it, I extend the bit down as far as the drill press will go, then, with a junk bit in the chuck, lightly clamp the vise to the end (to center the vise on the axis of the bit). Then while bit is still down and vise still clamped on junk bit, I secure the table on the press and clamp the vise to the table. Then I can release the bit from the vise, thereby letting the drill press head return to the resting position.
All blanks put into the vise from that point (as long as table and vise remain secure) is sure to be centered.
Obviously, the junk bit is so you don't dull a good bit by clamping it.