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  1. #31
    Mustafa Umut Sarac's Avatar
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    I learned that the real problem is subsurface cracks after grinding

  2. #32
    Greg Davis's Avatar
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    The lenses come as a disc about 3/4 inch thick. One side is already curved and polished, different curves are available to create different strength lenses. We mark up the lens for the prescription axis, then attach a metal block to the front side with wax. This block gives the lathe chuck something to gab onto. The machine is closed so particles don't go everywhere. A standard shop-vac is attached to suck up powder. Polishing cannot be done on this machine since it requires a liquid medium. The bit cuts the backside to achieve whatever amount of curve is necessary to create either a positive or negative lens. For the fining and polishing steps, we place grit pads (felt for polishing) on ceramic tools called laps. These tools are curved to match specific lens diopters, but often we need to carve custom laps for specific needs. This is done on the cnc lathe from styrofoam blanks. The lap matches the curve we cut into the lens. After the prescription is put into the lens, we cut the lens to the shape of the frame.

    There are new machines being introduced that allow us to skip the fining process and go straight from the generator (the name of the lathe) to the polisher. These are very expensive.
    www.gregorytdavis.com

    Did millions of people suddenly disappear? This may have an answer.

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  3. #33
    barryjyoung's Avatar
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    Quote Originally Posted by freygr View Post
    Unluckily the chips (material taken off by the cuter) is GRIT and it is abrasive, Silicon Oxide one of the many choices of sand paper. The final polishing of the lens used very fine abrasive. The lathe used in the lens cutting is not a standard Machinist machine tool.
    Silicon Carbide or Aluminum Oxide are the two most common abrasives used in sandpaper.
    Barry Young
    Young Camera Company

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