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  1. #11
    Chris Lange's Avatar
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    Expecting to create a lens from blanks with no polishing stage whatsoever, and only a grinding stage is a ludicrous idea. Trust me, I've done it by hand using blanks I rolled myself from molten glass.

    With glass or plastic you will need multiple stages of polishing, with glass you work down to a mixture of crushed-up sea creatures called Cerium, and do that two or three times to give the glass as perfectly smooth a finish as possible...yet even then without serious lensworking equipment the glass will not be as smooth as a cheap projector lens.
    See my work at my website CHRISTOPHER LANGE PHOTOGRAPHY

    or my snaps at my blog MINIMUM DENSITY
    --
    If you don't have it, then you don't have it.

  2. #12
    AgX
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    Umut, for milling metal an emulsion of special oils in water is applied for cooling and rinsing. For plastics I just would use water with surface active Agent. If at all.

  3. #13
    Steve Smith's Avatar
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    I can get a better finish laser cutting acrylic than I can CNC cutting.


    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  4. #14
    Mustafa Umut Sarac's Avatar
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    Thank you Chris and AgX.

    I opened an thread at cnczone and waiting answers.

    Umut

  5. #15
    Mustafa Umut Sarac's Avatar
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    Thank you for the tip Steve. How deep can a laser cut a cylinder in the acrylic mass and how depth effect the precision. How do you polish the Surfaces.

    Umut

  6. #16
    lxdude's Avatar
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    Quote Originally Posted by Steve Smith View Post
    I can get a better finish laser cutting acrylic than I can CNC cutting.


    Steve.
    Yes.
    I do use a digital device in my photographic pursuits when necessary.
    When someone rags on me for using film, I use a middle digit, upraised.

  7. #17
    lxdude's Avatar
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    A CNC could be set up to polish, on the idea that if a cutter can come into contact with a part, a polishing device could also be brought into contact with the part. Numerous polishing stages would still have to be done. I don't think it would be worth the cost to do it that way, but it is technically possible.
    I do use a digital device in my photographic pursuits when necessary.
    When someone rags on me for using film, I use a middle digit, upraised.

  8. #18
    richard ide's Avatar
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    AFAIK lens polishing using a pitch lap is capable of holding or adjusting curvature to approx 1/4 wavelength of light. I do not believe that a CNC generated profile would come close to that although possibly the highest quality machine (read highest cost) might come close. Having ground and tested a telescope mirror; I still marvel at the close tolerances obtained by a hand process. There is a very good reason that lenses are made the way they are.
    Richard

    Why are there no speaker jacks on a stereo camera?

  9. #19

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    Acrylic is "defrosted" by applying heat AFAIK, from a butane torch. It melts the surface and makes it transparent again. But you would get some distortions I believe.

  10. #20
    lxdude's Avatar
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    Quote Originally Posted by richard ide View Post
    AFAIK lens polishing using a pitch lap is capable of holding or adjusting curvature to approx 1/4 wavelength of light. I do not believe that a CNC generated profile would come close to that although possibly the highest quality machine (read highest cost) might come close. Having ground and tested a telescope mirror; I still marvel at the close tolerances obtained by a hand process. There is a very good reason that lenses are made the way they are.
    It would be a matter of having the equivalent of a pitch lap mounted to the CNC bed, to achieve the final curvature.

    And you are right about the precision possible with hand work. I worked in a shop that was making a small double side 7075 aluminum turbine impeller with extremely tight tolerance on perpendicularity to axis, and width and parallelism between sides. The brand new Hitachi CNC machine could not hold the tolerances. So they bought a new Sunnen (top name) machine to lap the two sides into parallel while maintaining perpendicularity. It couldn't do it without taking way too long- a serious production bottleneck. We ended up doing the finish work by hand using a surface plate with sandpaper taped to it. After a little experience, it was easy to judge the amount of pressure to use and where to apply it. Measure, sand on 400 grit, repeat as necessary. Switch to 800 grit to refine the finish and bring to final size, then put the part in the Sunnen to establish the final finish, or switch to 1500 grit paper and do it by hand.

    The final finish was not necessary to bring the part into surface finish spec., but established the look expected of precision machine finishing.
    It was a political thing. They bought brand new machines that "of course" could do anything the salesman said, and if the machines couldn't, it had to be our fault-they would not accept that hand finishing could be more precise than one machine and faster than the other.
    I do use a digital device in my photographic pursuits when necessary.
    When someone rags on me for using film, I use a middle digit, upraised.

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