Qualifying large table question
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  1. #1
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    Default Qualifying large table question

    Hi all,
    I own a 48x30 cast iron surface table. Visually it looks pristine, but I have no calibration data.
    I need a smaller plate anyway, probably 18" square.
    Given this one will be new and have a calibration can I use it to qualify my larger table as "good"?
    I was thinking overlapping prints should work, but I've not had to do anything like this before.
    I also have a very second hand 24" square plate that I would like to learn scraping on. It came with a machine, so was effectively free. Can I scrape in 18" of it, then move and do the last 6" to match? Sort of the same question, but I don't intend to touch the table, just understand it's flatness ( or not)

    Dave

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    Quote Originally Posted by small.planes View Post
    Hi all,
    I own a 48x30 cast iron surface table. Visually it looks pristine, but I have no calibration data.
    I need a smaller plate anyway, probably 18" square.
    Given this one will be new and have a calibration can I use it to qualify my larger table as "good"?
    I was thinking overlapping prints should work, but I've not had to do anything like this before.
    I also have a very second hand 24" square plate that I would like to learn scraping on. It came with a machine, so was effectively free. Can I scrape in 18" of it, then move and do the last 6" to match? Sort of the same question, but I don't intend to touch the table, just understand it's flatness ( or not)

    Dave
    I suspect you could use the 18x18 to scrape in a 24x24 if you work carefully. A 48x30 is going to be a lot harder. The small plate can be used to check local flatness (holes and humps) but you'll need other techniques to check overall flatness. Precision levels, autocollimator, reference straight-edge, etc.

    This post might get better answers in the machine reconditioning and scraping forum. I'd definitely like to hear Richard King's opinion.

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    i once corrected a 40" straight edge on a 32" plate. it would not seem like a big deal, but was a total pain and took several times longer than on a larger plate and in the end i cant really be sure what the result is.

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    Quote Originally Posted by small.planes View Post
    Hi all,
    I own a 48x30 cast iron surface table. Visually it looks pristine, but I have no calibration data.
    I need a smaller plate anyway, probably 18" square.
    Given this one will be new and have a calibration can I use it to qualify my larger table as "good"?
    I was thinking overlapping prints should work, but I've not had to do anything like this before.
    I also have a very second hand 24" square plate that I would like to learn scraping on. It came with a machine, so was effectively free. Can I scrape in 18" of it, then move and do the last 6" to match? Sort of the same question, but I don't intend to touch the table, just understand it's flatness ( or not)

    Dave
    Repeat O Meter used for checking before and after lapping, some use 100mm precision level .02mm/m but obviously need plate level or vial bubble will be off scale
    Attached Thumbnails Attached Thumbnails repeatometer.jpg  


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