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  1. #1
    plh's Avatar
    plh Guest

    Default Question concerning mirror making project



    Hello, people of sci.astro.amateur,
    I am working on an independent study project that involves making a
    small telescopic mirror. The professor's idea is to turn the mirror
    out of aluminum or perhaps stainless. We have access to CNC machinery
    and can turn a parabola according to a formula within accuracy of
    +/-.0005". The blank will be about 2" diameter. Then we would grind
    and lap it, then platinum plate through deposition.
    My question to the good people of this group is, does this sound
    feasible? This project is not for looking at stars. It has to do with
    creating special eyeglasses. Once finished, a small rectangular
    section will be removed then embedded in the eyeglass lens. But I am
    not here to debate the pros or cons of that part of it. It is the
    mirror part I was looking for feed back on, or for leads about which
    sources of information might be helpful.

    Thank You,
    -plh
    --
    I keep hitting "Esc" -- but I'm still here!
    [if "123" is in email address, that is an anti-spam thing.]

  2. #2
    Tim Killian's Avatar
    Tim Killian Guest

    Default Question concerning mirror making project

    What you describe probably would work, but why the platinum reflective
    layer?

    plh wrote:



  3. #3
    Adam Norton's Avatar
    Adam Norton Guest

    Default Question concerning mirror making project

    An aluminum surface is nearly impossible to polish to anywhere near the same
    quality as a glass surface. What can be done is to deposit a few mils of
    electroless nickel and then polish that. Stainless steel can take a
    somewhat decent polish.

    You do not mention how short the F.L is on this parabola or what the figure
    error tolerance is. Polishing something that deviates strongly from a
    sphere is very difficult while still keeping a good figure. Remember that
    usually 50% of any optical design project is doing the tolerance analysis.

    There are many vendors who can turn this kind of part to optical tolerances
    with no need for further polishing (except for the most exacting
    applications). Search for single-point diamond turning vendors. Netoptix
    (http://www.corningnetoptix.com/) is one of the best but not necessarily the
    cheapest. If you do choose to use single point turning, cut the blank to its
    finished rectangular shape first, then turn it. Multiple blanks can be held
    on a single spindle during turning.

    I also have to ask why coat it with platinum? If you are looking for
    durability, such mirrors are usually coated with rhodium which has much
    better reflectance.

    --
    Adam Norton

    Norton Engineered Optics

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  4. #4
    Jeff Lowe's Avatar
    Jeff Lowe Guest

    Default Question concerning mirror making project

    plh wrote:

    You gotta love it when professors reinvent the wheel for the Nth time.
    Diamond turned freeform molds for eyeglasses are common in industry.
    Companies such as Optical Electroforming specialize in this type of
    work. http://www.opticalelectroforming.com...d/diamond.html
    The molds are turned in electroless nickel and have an off the machine
    form accuracy of about +/- 0.000001". The form of these molds does not
    have to be rotationally symmetric, and in fact these machines are used
    to produce torics, bifocals, and progressive prescriptions.

    BTW, stainless cannot be diamond turned. The iron in steel has an
    affinity for the carbon in the diamond tool.

    --
    jeff


 

 

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