OO> of the tile on the tools edge. Now I'm at 220 grit and I can see the OO> tiles at the edge are slowlly disappearing.
OO> So, what do I do now ? Do I need to cover the entire tool with new OO> tiles
Robert,
You could affix a new set of tiles to this tool, but it would be about as easy to pour a new tool on the sagged mirror. I had a similar experience with the 12.5" f/7.5 that I'm working on. I had ground the mirror all the way through 3 micron and then poured the pitch on the lap (raised tiles with channels). In the process of polishing, I screwed up and got some scratches on the surface too deep to polish out and needed to go back to medium grinding to remove them.
I couldn't remove all the pitch from the tool, so I poured another one. I went back to 220 to reestablish my contact and did so in short order. You shouldn't have trouble getting contact with a new tool.
Of course, you could just finish grinding with a sub diameter tool...which is what you have with the used up tile tool. Many mirrors have been completed with a tool not as large as the mirror. My biggest concern would be that the ultra thin tiles at the edge of the tool might chip and scratch the mirror.
Mike * RM 1.3 * If I want your opinion I'll beat it out of you!