[ATM] Cracked Mirror Update and a Question

["Dave Jack" <dave.jack@glass-beads.net>]

Hello all;

For those who responded to my queries about a cracked mirror blank and
wondered what ever became of Dave's dilemma I can say I have moved on. I
ground as far into the blank as I could with #220 SiC to remove the crack
but no luck. I thought about putting a few drops of dilute HF acid and
surfactant in it, not sure where I read about that or if it came from the
list. Seemed like a good idea to try and round out the root of the crack and
help prevent it from propagating but I took a pass on it and mulled things
over. Richard suggested fusing the crack...great idea and very odd that he
suggested this not knowing I am sitting next to an annealing kiln large
enough for the job. This I would have gone for if I had a rampable temp.
controller, I was just waay too lazy to manually ramp the temp is what it
came down to.

So what happened? I ignored the crack, finished the fine grind and have
moved on to polishing. If the mirror cracks so be it, I am not going to
worry too much. I have found the whole lap thing to be a bit of an ordeal.
The lap and I don't really get along too well and it is only after 3hrs or
so of actual polishing time we have started an uneasy truce. Trimming and
maintaining the lap have driven me to distraction. I swear I spend more time
trimming than polishing although I know that's not true, it just seems like
it. The thing is this: I have thinned out the lap now so that it is only
about 1/8" thick and I am only 3hrs into polishing an 8" mirror. Room temp
has been on the low side, 15 to 18C so its not that I have thinned it out
working too hot I just don't think I poured enough of a lap to start with.
So, here is the question: is it time to abandon this lap and pour another?

-Dave

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