ATM Hogging to Tile Tool

[Andrew Lin <alin@qualcomm.com>]

I've been hogging out my 8-inch mirror with a 2-inch
iron pipe end cap as per a suggestion from one of the
gurus in the San Diego ATM group.  I've reached my
desired focal length, as measured with the "reflect
the sun off the wet mirror test".  However, there
is a 0.25 inch (6 mm) ring around the edge of the
surface that got little or no grinding done to it.

My question is this:  Should I go ahead and make my
tile tool and shift grits, or should I attempt to
remove this ring, and then grind out the center more
to maintain my focal length?

/|_