On Thu, 26 Jul 2007 07:39:21 -0700, "
wrote:

......
Finding the center [of a threaded bore] isn't as difficult as it seems since
you can use the drill-press and a piece of dowel to spin the fitting
(by hand) whilst pressing it against the pointed end of a tack driven
through a board... even stiff cardboard would work. The trick here is
to first chuck a pointed scriber and use it to 'index' the point of
the tack (or whatever). Once the two were aligned simply clamp the
board to the table and go about setting up some method of chucking the
fitting. The tack will remain centered relative to the chuck.

-R.S.Hoover

What I've been doing for relatively small holes is find some stock,
use my grinder to make a point with a very flat angle, chuck it and
file to insure the point is centered. Cut off the point and about 3/16
of the stock; drop this pointy-side up into the hole. Now I have a
reference point at the center of the hole.

Now, I'd like to understand the method you are describing (above):
I'm familiar with the trick of chucking a needle (or something very
small; I think there is something called a 'wiggler'??) and aligning
that with a point on the work. you seem to be transfering the location
of the tip of the needle to the tip of the tack on the drill press
table. 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