Current state of the art reference planes - Page 2
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  1. #21
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    Great book. As far as I know, even today, lapping/scraping surface plates in sets of three is still the best method, material must still be incredibly stable to start, and must be processed and used in an incredibly stable environment. If by "very difficult", you mean millionths, this is something that might be most practical to undertake yourself?

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    Quote Originally Posted by Kai Kendall View Post
    Great book. As far as I know, even today, lapping/scraping surface plates in sets of three is still the best method, material must still be incredibly stable to start, and must be processed and used in an incredibly stable environment. If by "very difficult", you mean millionths, this is something that might be most practical to undertake yourself?
    The requirement for 3 plates is for lack of a reference surface. Once you have an accurate reference you can make a plate one at a time. For plates too large to make in threes, an autocollimator will work to arbitrary size. But it's very slow.

    The small fraction of an arc second resolution possible with a pair of $12 2"/div vials and the differential capacitance bridge provides a reference plane. The floor under the plate is going to deflect as soon as you get near it. But if you know what the plate is doing then you can isolate the surface from the supporting system.

    I was given three 2"/div vials by someone who bought them without realizing they were much too sensitive for his purposes. I just bought 10 of the CA3039 diode arrays on eBay. Next up is a 300 KHz Wien bridge oscillator with less than 0.01% THD.

    Tenths are difficult, but achievable with patience and attention. A half tenth is a B grade gauge block, so now we're talking hard. Less than that becomes really difficult and at millionths it is very difficult. Temperature and all manner of things conspire against you.

    Despite this, amateurs routinely do optical work that exceeds machinist practice by an order of magnitude or more. And even professionals screw up. Remember the corrective lens that had to be installed on the Hubble telescope because they forgot to account for gravity when figuring the mirror?

    I'm of the "if it's not difficult to do, why bother" school. It took me 40+ years to get there, but I put some Bonnie Raitt CDs I had not listened to on the other night and played along alternating between playing chord sequences and single string lines. I have the same sense of blues style, so as soon as I could spot the key I could play along. Nothing is so satisfying as achieving something it took you 40 years to accomplish. I've been able to do it on harmonica for over 30 years, but guitar always eluded me. And I still have only a toe hold. Joe Pass level is still a long way off. But maybe, just maybe, before I die I can put a random Joe Pass recording of a tune I've never heard before on and play along.

    BTW Wheels17, Thanks for the link to Richard King's thread on 3 point support. It was very interesting. The optimal support points for an arbitrary object would require a finite element based search which is computationally intractable. I find it sad that most people are so distracted by new whiz bangs that they lose sight of the fundamentals.

    Have Fun!
    Reg

  3. #23
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    Quote Originally Posted by rhb View Post
    And even professionals screw up. Remember the corrective lens that had to be installed on the Hubble telescope because they forgot to account for gravity when figuring the mirror?
    Have Fun!
    Reg
    It was actually an error in a measuring instrument that was used to check the mirror during the figuring. A lens was displaced by a millimeter from where it should have been, causing the Hubble mirror to be shaped incorrectly. A costly mistake, but somewhat fixed when a replacement for the original WFPK camera was installed during a Shuttle mission.

    https://www.newscientist.com/article...mirror-fiasco/

    Wide Field and Planetary Camera 2 - Wikipedia

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  5. #24
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    Thanks for the links. I'd wondered about the details, but finding more information was pretty much impossible even if you had internet access in 1990. All I had ever seen were very vague news reports by "journalists" who are not known for getting their facts straight. And seem of late to have dispensed with facts entirely in favor of expressing their personal opinions.

    A little disturbing that our primary builder of spy satellite cameras would make such a glaring mistake on a public job. How much have mistakes building classified cameras cost the taxpayers?

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    Quote Originally Posted by rhb View Post
    Thanks for the links. I'd wondered about the details, but finding more information was pretty much impossible even if you had internet access in 1990. All I had ever seen were very vague news reports by "journalists" who are not known for getting their facts straight. And seem of late to have dispensed with facts entirely in favor of expressing their personal opinions.
    The information has always been out there, you just had to be reading the right material.

    Nothing to do with vague news reports by "journalists", if you get your info from National Enquirer etc your liable to be minimally informed.

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    Obviously your were not using the Internet in 1990. In those days we used ftp, usenet and plain ASCII text mail. It was a *very* different world. You had a list of ftp servers you checked manually to see what was there. Gopher was an early attempt at automating searching ftp servers which appeared in 1991.

    A high speed connection for an entire corporation was a 1.4 Mb/s T1 link. Mere mortals used 9600 baud Telebit Trailblazers if they could afford the $1000+ cost.

    Rest assured the "NewScientist" article was most emphatically *not* on the internet in 1990. I was working at a major oil company research lab when we finally got access to the Internet in fall 1989 or spring 1990. The Stanford grads had been lobbying for access for several years as they had been on ARPAnet in grad school.

    From Wikipedia:

    "English scientist Tim Berners-Lee invented the World Wide Web in 1989. He wrote the first web browser in 1990 while employed at CERN near Geneva, Switzerland.[2][3] The browser was released outside CERN in 1991, first to other research institutions starting in January 1991 and then to the general public in August 1991. The World Wide Web has been central to the development of the Information Age and is the primary tool billions of people use to interact on the Internet.[4][5][6]"


    In 1991, Bob Metcalfe, the inventor of ethernet, wrote a piece for "Unix Today" predicting that Mosaic would crush the Internet. We capitalized Internet back then.

    It was not of sufficient concern for me to go back many years later to research the subject. Mostly, I just never thought about it again.

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    Quote Originally Posted by triumph406
    The information has always been out there, you just had to be reading the right material.
    Quote Originally Posted by rhb View Post
    Obviously your were not using the Internet in 1990. In those days we used ftp, usenet and plain ASCII text mail. It was a *very* different world. You had a list of ftp servers you checked manually to see what was there. Gopher was an early attempt at automating searching ftp servers which appeared in 1991.

    A high speed connection for an entire corporation was a 1.4 Mb/s T1 link. Mere mortals used 9600 baud Telebit Trailblazers if they could afford the $1000+ cost.

    Rest assured the "NewScientist" article was most emphatically *not* on the internet in 1990. I was working at a major oil company research lab when we finally got access to the Internet in fall 1989 or spring 1990. The Stanford grads had been lobbying for access for several years as they had been on ARPAnet in grad school.
    They had these things called newspapers and magazines in 1990, as well as some advanced technology called television and radio. The results of the Allen Report (detailing the problems with the Hubble) were widely reported in the media.

    PROBABLE MISTAKE IN HUBBLE IS FOUND - The New York Times

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    Quote Originally Posted by rhb View Post
    ......

    It was not of sufficient concern for me to go back many years later to research the subject. Mostly, I just never thought about it again.
    Is there any point into going I or who "invented" the internet?
    90's ... really? Guessing that as your point of entry which we all think as the "new days".
    Others will have differing points of origin.
    For me the internet started in the mid 70s which was the first time I could link multiple computers working in parallel on a problem.
    20 machines with the combined power of less than a cell phone or even a dishwasher now....
    But at the time, I have so much power at my hands, gonna crack this basic AI 50 level deep net.......
    Bob

  11. #29
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    None of this has anything to do with the actual thread topic, defining a flat surface to very high precision.

  12. #30
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    Quote Originally Posted by rhb View Post
    Obviously your were not using the Internet in 1990. In those days we used ftp, usenet and plain ASCII text mail. It was a *very* different world. You had a list of ftp servers you checked manually to see what was there. Gopher was an early attempt at automating searching ftp servers which appeared in 1991.

    Rest assured the "NewScientist" article was most emphatically *not* on the internet in 1990. I was working at a major oil company research lab when we finally got access to the Internet in fall 1989 or spring 1990. The Stanford grads had been lobbying for access for several years as they had been on ARPAnet in grad school.
    I didn't say the article was availible on the internet in 1990, but I'm sure it was online then in one form or another.

    In 1990 I was reading the LA Times (subscribed every day 1986-1996) listened to the radio, watched documentaries, worked in aerospace, read technical magazines, read technical articles in the McDonnell Douglas library, etc etc, you know gathered information the "old school" way.

    Ask your questions over on Quora, more your level of understanding

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    Anyone actually interested in the subject can follow it here:

    suggestions for high-resolution tiltmeter (inclinometer) sensor? - Page 11

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    Walking thru Boeing Surplus back when it was a storefront there was a CMM base for sale. Maybe 4' x 4' x 1' but sitting on a pedestal of another piece of pink granite of similar size. Had some kind of elastomer/epoxy between the two pieces. I have no idea how well that worked. :-)

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    The hobby hologram crowd uses a large box of sand on partially inflated inner tubes to provide isolation from optical scale vibrations.

    I expect that the dimensions of the two masses and the elastomer properties were chosen to provide damping at frequencies of the critical noise at that location. For a machine like that you would make a site survey. Road traffic and ocean surf would be important noise sources.

    The arrangements for IC processing which are sensitive to vibration have extremely elaborate damping systems which are completely isolated from the building and almost completely decoupled from the earth itself.


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