[ATM] Yet another hogging question

["Bill Wheaton" <billwheaton@gmail.com>]

I've been reading this list for a while and searching the archives, but
haven't found something like this...

I have come into a 12.5" full thickness pyrex mirror blank and matching
plate glass tool 3/4" thick ground and polished to f/8, but I am going to
grind it to f/5.5.  To that end, I still have a good bit of glass to remove
-- about 0.05" or so?.  So I need suggestions on which way I should go with
this.  Should I use the tool, or should I put it aside, and hog it out with
an iron pipe cap and go with a tile tool with all the advantages it has?  I
ordered a 12.5" grit kit from Tom at GotGrit, and I got an extra pound of
#60 for good measure.

I tried using the metal pipecap today, and while it seemed to grind ok,
there is no extra pressure with it other than what I can put on with the
heel of my hand.  Would a flat 3" flange work better, since it has more
surface area?  It seems like doing it this way will take forever, since the
surface area of the iron ring is so much smaller than a plate glass tool.

I've already put about a 1/8" bevel on both the mirror and too, and ground
the back of the mirror against the back of the tool (ugly mold marks there
are almost gone).  I also read the "Grind More Worry Less" rule, so if this
breaks that, let me know :)

Thanks for any help.

-Bill Wheaton
Decatur, GA
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