Flatness evaluation through autocollimator -Info / Advice needed
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  1. #1
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    Default Flatness evaluation through autocollimator -Info / Advice needed

    Hi,

    Need some advice on some good source for evaluating Flatness of for example a surface plate by some numerical method, by hand or excel.

    Straightness seem straight forward but its the connecting of data sets och evaluating the resulting minimum flatness the gives me some headache.
    As this been done for decades there should be some good book / reference / instruction on it somewhere to be found? Ive googled a fair bit but my thinking is that electronic A-Cs were common already prior to internet, as not much shows up beyond basic straightness and various possible set-ups, but little on actual hands-on evaluation. Plenty of expensive programs though...

    At my hand:
    A one axis 0,5" analog auto collimator with two mirrors, one perpendicular on stand and a front end mounted 90degree deflector.

    It appears o be in good working order, lights, adjustments etc. I assume it would benefit from a calibration before doing any real work but first Id like to see I can master the the actal data evaluation.

    Thanks for any input!

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    Quote Originally Posted by Lumberjack View Post
    Hi,

    Need some advice on some good source for evaluating Flatness of for example a surface plate by some numerical method, by hand or excel.

    Straightness seem straight forward but its the connecting of data sets och evaluating the resulting minimum flatness the gives me some headache.
    As this been done for decades there should be some good book / reference / instruction on it somewhere to be found? Ive googled a fair bit but my thinking is that electronic A-Cs were common already prior to internet, as not much shows up beyond basic straightness and various possible set-ups, but little on actual hands-on evaluation. Plenty of expensive programs though...

    At my hand:
    A one axis 0,5" analog auto collimator with two mirrors, one perpendicular on stand and a front end mounted 90degree deflector.

    It appears o be in good working order, lights, adjustments etc. I assume it would benefit from a calibration before doing any real work but first Id like to see I can master the the actal data evaluation.

    Thanks for any input!
    .
    as any instrument focused on infinity you usually deal with width of reticle for example 10 arc second wide or 5 arc second wide reticle with 1 arc second being .0006" per 10 feet.
    .
    so if focused at 10 feet and i got a ruler scale in view and reticle appears .006" wide at 10 feet thats 10 arc second wide reticle. just saying when you hear talk of its within 1/4 arc second if thats 1/40th the width of reticle line you can barely see maybe 1/2 of crosshair width resolution maybe 5 arc seconds. resolution is where if you got a ruler the lines blur together rather than read distinct lines. normally cannot read a 1/100" ruler at 100 feet for example. Brunson Instruments still makes optical instruments and they have manuals to use them online.
    .
    just be aware you can take 10 readings and average and say its within 1/4 arc second but thats like reading a 1/100" ruler and saying you can measure .001" by averaging 10 readings.


    Brunson Instrument Company

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    Look for the Federal Standard (the number escapes me at the moment) that covers surface plate tolerances and grade classification. I believe I have seen the test method explained in that standard.

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    Quote Originally Posted by specfab View Post
    Look for the Federal Standard (the number escapes me at the moment) that covers surface plate tolerances and grade classification. I believe I have seen the test method explained in that standard.
    http://doxcalibration.com/wp-content...GGG-P-463c.pdf
    http://www.tru-stone.com/pdf/FedSpec...ndment%201.pdf

    dee
    ;-D

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    Google search (moody method surface plate calibration)

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    Thanks everyone for great input!
    Got alot of reading to do now, already thinking too far ahead and started planning how to fit a camera and make some more mirrors, maybe from HDD discs..

    One of the things I found this evening was Surfaceview program from Vermonts Photonics, but I could not get the installer running, anyone used it lately? Ill be sending them an email tomorrow.

    Cheers!
    H


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