Re: ATM Which tool?

["Dave McCarter" <dmccarter@sympatico.ca>]

> 1) hog out with the iron weight then build a tile tool with the hex tiles
> for fine grinding. However as I understand it the tiles will damage the
> surface of the glass as they "mate" to the surface.

No worse than the barbell!  The idea is to get close to the proper depth any
old way you can, and then mate the tiles to the mirror with the next size up
grit. So if you rough with 80, set the tiles with 120. The tiles will wear
in at about the same rate as the mirror surface loses all the damage the big
grit causes. This will still leave you plenty of tile to do a fine job with
each succeeding grit size. Imagine if you were to rough out with the tiles,
then start going finer, only to have tiles too thin and breaking off at the
600 grit stage. There would be nothing for it but to put on new tile and go
back to 120. I know, a friend was in that very situation several years ago!

> 2) build a grooved glass tool with the thick glass squares the same way a
> tile tool is built and both hog out and fine grind with this tool. Do I
have
> to continually re-bevel each individual square of glass on the tool as the
> bevels wear out or not?

I picked up a 12.5 inch pyrex tool some years ago. It had nasty channels cut
deeply into it, but the surface was at least concave as the tool had been
used to make a large lens. I made a tool with 10mm thick plate tiles, each
tile 1 inch by 1.5 inch. The epoxy held pretty well and I was able to get
rid of all the score marks, except for a 1/8 inch mark on the very edge,
which I refer to as my fiducery mark. I never found it necessary to worry
about beveling the edges of the glass tiles, and that would have been a
horendus job. Once the mirror was ready for more grinding I made a tile tool
and started at 120.  I recently got back to that glass, and it is almost
polished out.

Dave