Jim Wilkins wrote:
On May 25, 8:35 pm, Spehro Pefhany
wrote:
...
I guess if I had a setup that would hold a dial indicator in the
spindle and would reach the outer rim, I could just rotate the spindle
and adjust X/Y. Might be easier since there is no spindle lock on my
X3.
Spehro Pefhany

The simple version of that setup is an L shaped piece of stiff wire.
Chuck the short end, cut the long one to just clear the column. A
Starrett Last Word will clamp directly on the wire, otherwise make a
little block to fit the test indicator's dovetail. I would size the
hole in the block for 1/4" rod. While you are set up to cut the
dovetail you could make a lathe holder too.

To roughly center something into the range of an indicator I center a
6" ruler on it and move a point in the chuck to the 3" line. Usually
this gets it within 0.010".

Quick way to get a center (close)
Use a postcard or other rectangular cardstock with crisp edges.
Place the card on the round workpiece such that one corner is at an edge.
Mark where the two adjacent sides intersect the edge of the disc.
Connect those two marks with a line, which intersects the center
Move the card approx 90 degrees and repeat for an intersecting line.
The intersection is the center.