Re: [ATM] Cracked Mirror Update and a Question

[hermit <hermit@outofoptions.org>]

Does your blank have a usable back?

Dave Jack wrote:

>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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