RE: [ATM] mirror grinding

[GARY FUCHS <gary@rcn.com>]

>>The grinding tool does not have to be round, however, if it is square, I
suggest cutting the corners off of it.   Yes, if you can find a flat rock,
that can be used as a hog out tool.  However, aluminum works much faster.

Thanks. Can I ask a couple more...

I can get steel for $0.18/lb vs $1 for Al and stainless - is there enough of a 
difference to justify the more expensive metal? 

Is there an ideal ratio of tool diameter and contact area to glass diameter? For a 12" 
how would a brake rotor do - I'm thinking of working with the wide part, about 8 - 
10", holding the smaller section (where the wheel mounts). Or would a simple ring 
do just as well?

Thank you,

Gary Fuchs
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