OO> I have a 12.5" plate glass blank which is _not_ precurved -- but I OO> want to make a f/4 and am concerned that the tiles will grind right OO> through on the edge if I don't pre-curve the tool. I also expect OO> hogging out to proceeed more rapidly with a precurved tool. Steve,
The tiles might wear through on the edges of the tool during hogging out but, so what? Go ahead and hog it the rest of the way with the resulting "sub diameter" tool <g>. When you have the correct sag and are ready to move on to 60 or 80 grit, pour another tool on the newly sagged mirror. This second tool should easily carry you through fine grinding and you can use the original tool as a base for the pitch lap.
Mike
* RM 1.3 * If I throw a cat out the car window, is it kitty litter?