Re: [ATM] Doh! Deep Crack in Mirror

[Richard Ozer <rozer@pacbell.net>]

Ouch.  That's kind of deep.  It will take a while to grind them out... certainly as much 
(if not more) time than if you had started with a flat blank to begin with.  Chances 
are, the damage extends deeper than what you can see visually.

If I were you, I'd just ignore it and pretend it never happened.  There will be no 
obvious affect on the mirror's performance; especially if the damage is in the center 
(the center is shadowed by the telescope's secondary).  The only thing you should be 
concerned about is any glass chips coming off the damaged area and polluting one of your 
wets while fine grinding or polishing.. fragments can lead to scratches.  However, 
spending enough time with 220 grit will likely eliminate that risk.


RO

Dave Jack wrote:
> Hello all;
> 
> Well for those who said not to worry about my pre-generated mirror and tool
> not fitting exactly you couldn't have been more right. The "bump" in the
> middle of the tool was gone so fast at #320 grit that I couldn't even tell
> you how many strokes it took. Gone in 3min for sure.
> Now comes the interesting part....during clean-up I forgot I had placed my
> mirror in my water bucket, now milk white from grit and fines, then grabbed
> my tool and plunged it into the water bucket. I smacked the tool almost dead
> center into the mirror. No chips just 3 cracks varying from 2 to 4mm in
> length and unknown depth. I want to say the deepest crack terminates 300
> microns or so below the mirror surface but I know the light can play tricks
> with my eyes. In reality it could be much deeper.
> I am guessing I will be grinding this out with a heavier grit. Do I need to
> order #80 grit? The coarsest I have is #220 SiC but if I need to make a call
> to gotgrit.com so be it. As always, thanks for any and all help.
> 
> -Dave
> 
> 
> 
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