Who can do inside surface finishes in single-digit microns? - Page 2
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  1. #21
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    Quote Originally Posted by 9100 View Post
    When you think about it, one micron is about 40 millionths of an inch, not very smooth. I would get it as smooth as I could with a hone or lap, then electropolish it. Astronomical mirrors have aluminum evaporated on them, then coated with silicon monoxide.

    Of course, I don't even know why we are worrying about it. One of the most irritating features of these forums is people who come in with a problem, then refuse to furnish enough information to make a meaningful recommendation.

    Bill
    Astronomical mirrors are aluminized because glass substrates that provide useful reflective optical surface figure don't reflect visible light very well.

    Aluminization of an aluminum substrate is a rare occurrence.

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    Quote Originally Posted by CalG View Post
    I find it equally irritating that a simple question can not be responded to.

    Can anyone provide a 2 micron or better surface roughness on an aluminum id? |Nothing more was asked.
    True, but it was also an incomplete one. For example, is the hole bored clear through or blind? How long is the bore? What alloy of aluminum? Is the aluminum cast or rolled? Either way, the grain is going to get in the act. When I was making mirrors, I had some interesting discussions with Bob Cox, who made the optics for the Gemini space program and edited the Amateur Telescope Maker column in Sky & Telescope. His view was that because aluminum has grain, I would never be able to produce a mirror with the same performance as a glass one, which is amorphous. I agree, but my application was not as demanding as an astronomical mirror. I never tested my mirrors with a profilometer, but I am sure they were better than 1 micron. If I can pick the length of the tube and the alloy, I am sure I could make one with a 1 micron finish, but these are unknown in this case.

    Bill

    PS It may well be that the OP doesn't need a polished bore at all, but a glass rod acting as a light pipe, but I resisted the temptation to redesign his device.

  3. #23
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    Lacking more info, I'll assume a can of Mother's Mag Wheel Polish could give the required finish.

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    Isn't 1 micron equal to 40 microinches? That is hardly a difficult requirement.

    Now if the OP actually means single digit microinches, that is only slightly more difficult.

  6. #25
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    Quote Originally Posted by Conrad Hoffman View Post
    Lacking more info, I'll assume a can of Mother's Mag Wheel Polish could give the required finish.
    To test your theory, I took a can of Mothers, chucked into the lathe, and tried to create the geometry requested. All I wound up with is a gooey mess of abrasive slop all over the lathe, which I think conclusively proves you wrong.

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    Quote Originally Posted by Milland View Post
    To test your theory, I took a can of Mothers, chucked into the lathe, and tried to create the geometry requested. All I wound up with is a gooey mess of abrasive slop all over the lathe, which I think conclusively proves you wrong.
    Well, clearly you started from the wrong end.

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  10. #27
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    Quote Originally Posted by specfab View Post
    Well, clearly you started from the wrong end.
    I have a second can, I can try it your way. Give me a few days...

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    Quote Originally Posted by 9100 View Post
    True, but it was also an incomplete one. For example, is the hole bored clear through or blind? How long is the bore? What alloy of aluminum? Is the aluminum cast or rolled? Either way, the grain is going to get in the act. When I was making mirrors, I had some interesting discussions with Bob Cox, who made the optics for the Gemini space program and edited the Amateur Telescope Maker column in Sky & Telescope. His view was that because aluminum has grain, I would never be able to produce a mirror with the same performance as a glass one, which is amorphous. I agree, but my application was not as demanding as an astronomical mirror. I never tested my mirrors with a profilometer, but I am sure they were better than 1 micron. If I can pick the length of the tube and the alloy, I am sure I could make one with a 1 micron finish, but these are unknown in this case.

    Bill

    PS It may well be that the OP doesn't need a polished bore at all, but a glass rod acting as a light pipe, but I resisted the temptation to redesign his device.

    Bill

    You have now posted the questions that are relavent to the OP question. Thank you.

    Heck, it might be some sort of energy dump. Just get it down the hole!

  12. #29
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    This is a somewhat dispiriting thread. With a Sandvick diamond tool on a Haas TL-1 we were recently able to get substantially sub-micron finishes on inside and outside bores in acrylic. For something to be optically clear you need roughness substantially below the wavelength of light, so well below 500nm. I am absolutely not an expert here but I was googling around and it would seem that good optical clarity, which literally means you can see through it, or see reflection off it and the glass doesn't degrade the image, is achieved with roughness on the order or more like 50nm or better. So I would say you can hit that on a TL-1 in acrylic. I can't tell you the SFM and coolant strategy as I didn't do the work myself. So I think there's a good probability you could do it in aluminum if you could manage the chip and such. Complex inside bores such as parabolas or hyperbolas at least several inches in diameter by a foot or two long were made for cosmic background measurements in the microwave range. I remember when this was being done in the early 90's at the University of BC there was some challenge in figuring out where to get it done but there were specialists they were talking to.

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    Bob Cox made experimental lenses and mirrors from Plexiglas. I think he polished them with a silver polish called Silvo, but that is a 50 year old memory. Interesting that he had the resources of McDonnell Aircraft and bought his polish in grocery stores. If I made plastic mirrors he offered to aluminize them but I never took him up on it.

    One time I commented that a lot of experts were so close mouthed about their techniques. He replied that he had been vaccinated with a phonograph needle. Nice fellow.

    Bill

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    Quote Originally Posted by gbent View Post
    Isn't 1 micron equal to 40 microinches? That is hardly a difficult requirement.

    Now if the OP actually means single digit microinches, that is only slightly more difficult.
    That was my point exactly. Any decent lathe guy should be able to get a 1 micron finish in aluminum. But if we are actually talking about micro inches, that is a bit of a different story. And the op did use both terms in his first post.

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    Quote Originally Posted by scraper View Post
    That was my point exactly. Any decent lathe guy should be able to get a 1 micron finish in aluminum. But if we are actually talking about micro inches, that is a bit of a different story. And the op did use both terms in his first post.
    Well, I can use "democrat" and "republican" in the same post, too, but that doesn't mean I don't know the difference. I was specific about the surface finish he says he thinks is needed, and simply observing that some here work in much smaller units. You could express the finish in microinches or parsecs if you chose to, but that wasn't the unit I expressed it in.

    In any event, someone was kind enough to agree to work with the guy directly. I hope it will be a productive relationship on both sides. This is all I was trying to achieve!

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    Is roller burnishing an option here, or are we outside its bounds?

    I've never used it as a process, I'm just curious.


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