Then you go on to find someway to chuck the irregular work.
Now I'm left with an irregularly chucked work and a reference point on
a board clamped to the drillpress table, very closely aligned with the
drillpress spindle. What does that buy me?? - Mike
----------------------------------------------------------------------------------------

You use a 'spud' -- anything that marries the part to the chuck in a
concentric fashion -- and use it to press the part against the tack/
center/whatever.

Once you know where the center falls you may drill & tap to use a bolt
as your new chucking piece, or attach a T-nut, centered on the new
mark, and so forth.

The purpose of the tack & cardboard is to transfer the center-point to
the opposite side of the irregularly shaped part, with the
understanding that using a tack and piece of cardboard is meant to
illustrate how the thing could be made up of whatever materials were
on hand.

-R.S.Hoover