You can also move the table/workpiece to the side, install you boring
set-up, move the workpiece back, adjust the height of the head/tool
(with the quill retracted), then re-center the cutting tool by rotating
the cutting tool by hand and moving the table until the tool tip
rotates concentric to the pre-drilled hole. You could also rely on the
x-axis/y-axis dials for repositioning (allowing for backlash by always
approaching from the same direction). Your previous post implied that a
drill hole was precise enough so these methods of repositioning should
also be good enough.
Alternatively just order a 12.5 mm drill bit (or a boxed set of metric)
via the Internet. A 12.5 mm drill bit is always good for drilling a
hole that needs to be reamed to 0.500". Other "odd sized" metric drill
bits can often be more useful than you would first think.
--- In firstname.lastname@example.org
> Part 1 was pretty imposssible for me because I had to first use a
> drill chuck with a pin to align the work piece in the vise and pre-
> drill the spot I was opening up, then remove the drill and drill
> chuck from the quill so I could install the boring head & cutter.
> Only way to do that was to extend the quill, adjust the head height
> so the center was true and then raise the quill so I could remove and
> replace the cutting tools. Ultimately that brought the quill further
> out than I would have liked. But your point is well taken.