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I am actually grinding my own lenses ( I am trying). Now I have been continuously using the chordal stroke for atleast 3 hours but i am unable to see any depreasion be it convex or conacve on the tool or the mirror respectively. I have been applying the chordal stroke properly using 60 grit carborundum. Further both the tool and the mirror have become foggy. How should I clean this. Should I directly use 400 grit or not. Can anyone tell me the correct procedure or a book that may demonstrate the same.

Shashaank
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    You want it to become 'foggy': you are making a ground glass surface. Much later on you will polish it to remove this. –  May 23 '16 at 17:55
  • @tfb yes presently i am using 60 grit.....i've been grinding for nearly 3 hours without any depression produced. And the mirror has become foggy as if the grains have penetrated it. So why hasn't any depression been produced. And how in future will i clean the tool and the mirror. Water doesn't seem to be an answer – Shashaank May 23 '16 at 18:13
  • See e.g. http://www.stathis-firstlight.de/atm/kyklopas_statusbericht_schl.htm for a description. The guy is making a really large mirror and he is experienced, so don't expect to proceed at the same speed. Even though the page is in German, you should be able to understand the durations ("Stunde" means "hour") and the carbo grits. Based on what I have read in the past, I don't think that going from 60 to 400 will give you a useful surface. – CuriousOne May 23 '16 at 19:00
  • @Shashaank The grit has roughened the surface which makes it appear sort of milky: if you wash it (to remove the grit) then you'll be able to feel that it's rough. Later you use a series of finer grits and polishes to take away this surface texture. (Disclaimer: I haven't done this but I did read a bunch about it, a long time ago). –  May 23 '16 at 21:28
  • @tfb Yes I think you've got it right. Even I am reading exactly this, right now on the internet. Thanku – Shashaank May 23 '16 at 21:35

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I'm not sure what you really wanted, but I assume you want to clean a foggy ( scratched ) lens.

There are many methods, but I know one here:
1. Use a very fine grade sand paper to sand it down as smooth as possible.
2. Use a torch to "partially melt" the surface of the lens and the surface tension of liquid will smooth it out.

The 2nd step requires a lot of skills, melting too quickly will deform your lens. You may need some practice on a spare surface before doing it on your actual lens.

MrYellow
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