Re: [ATM] Ain't got no shperometer

[Ken Hunter <atm_ken_hunter@yahoo.com>]

Normally, I'd agree to this and I do to a point... If you add "and are using the correct stroke". I would agree completely.
   
  Once you get a spherical surface it's fairly easy to go through the stages of finer and finer grit sizes. If you stick with mirror on top exclusively, you will continue to shorten the focal length of the curve. If the tool and mirror are of the same material and they wear at the same rate, you will remain spherical automatically * IF * the stroke length is correct. 
   
  For a beginner, it's difficult to know what the correct stroke length is and it's typical for the beginners stroke length to be too long resulting in a slightly depressed center of the mirror. This is mainly a "HABIT" learned during the HOGGING phase of the manual curve generation.
   
  It takes a while to re-learn the correct strokes used for grinding and then fine grinding. This is where the SHARPIE TEST is mostly used... To assist the optician with maintaining correct stroke length and curve on the glass during the changing grit sizes.
   
  If you have GROSS lack of sphericity, you should know it (without using a spherometer) by the feel of the disks sliding over each other.
   
  Ken Hunter
   
   
  
Guy Brandenburg <gfbrandenburg@yahoo.com> wrote:
  A reasonably decent spherometer that you can move from one spot to the other should be able to locate gross lack-of-sphericity if the measurements change noticeably. But, iIf you are dutiful in rotating everything frequently, systematically, and somewhat randomly when you grind with finer and finer grits, then it is very, very difficult to avoid getting something very, very close to a sphere.
Grind more, worry less.
Guy


       
---------------------------------
Get easy, one-click access to your favorites.  Make Yahoo! your homepage.
_______________________________________________
ATM mailing list http://www.atmlist.net/