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  1. #1
    BobL is offline Member: Blue and white apron brigade
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    Default Testing few Mics and callipers

    I was out at my former workplace today and I asked if I could borrow a 0.001mm micrometer so I could check some of my mics and callipers. I also borrowed a Mitzi digital calliper while I was at it.

    It's not what I would call a rigorous test which would involve a greater degree of cleanliness, some attempt at temp stabilised and maybe some repeated measurements

    Here is what I had to play with
    IMG_3309.jpg

    X is the Fowler 0.001mm mic from Work.

    A is a near new 150 mm ebay digital calliper that I keep at my electronics bench.
    B is a 150 mm, 6 year old calliper I bought from H&F and is my "general" shed calliper - its' pretty beat up, and after I dropped it several times, the thumbwheel on it disappeared. I also lost the battery cover on it and was using a piece of electrical tape to hold the battery in but miraculously found teh cover a few months later in a drawer.
    C is a second hand 0-2" 0.001" Mitzi mic I picked at a HTPA sale about 10 years ago. It was a bit rusty and appropriately priced. It came up OK although part of the scale is hard to read. I measured it up against another Mitzi at work and at the time it was spot on across the range .
    D is a new 300 mm ebay digital calliper I keep in my shed but I don't use it much.
    E is another H&F special that I picked up during a sale. It has not been the same since I dropped it. The readout occasionally jumps times it eventually it gives something close to the true value,
    F is a near new 25mm 0.01mm Mitzi that I use in my shed.
    G is a 200 mm ~5 year old calliper that I use a lot in my shed - It's the one I usually keep near my lathe/mill. It's been dropped few times. It no longer turns off and so says on all the time but I only need to replace the battery in it every 8-10 weeks.
    H is the Mitzi digital calliper I borrowed from work.

    For small measurements I measured individual feeler gauges while for larger measurements I used parallels. I tried as best I could to make sure the measurements were all done in the same spot on the feeler gauge or parallel but maybe I did not succeed and this may explain some of the scatter of the results.

    All measurements smaller than 25 mm are referenced to the Fowler Mic and the single ~150mm measurement (M) is referenced to the Mitzi calliper.

    (G) is a grouped set of ~6 feeler gauges to generate something thicker, I was not too careful about cleaning these so that could have contributed to the scatter.

    I was quite amazed to see that up to 25mm, apart from those G measurements, they all clustered close to the +/- 0.01mm.
    Where you don't see all 8 points it means that means some points are underneath others.
    NB the horizontal axis (Measurement) is shown as a log scale

    MicandCallipers.jpg

    I should add that this level of reproducibility may not be achievable in a real workshop situation when surfaces may not as flat/smooth as feeler gauges or parallels, or one is in a hurry, dirt etc.

    When I get a chance I will explore the 25 mm and upwards range a bit more.

  2. #2
    Join Date
    Sep 2012
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    Default

    Hi Bob,

    Those measurements are about what I would expect, particularly the digital ones.

    I've several cheap digital callipers and a 10 mm precision reference. At 10 mm all my instruments would show the same scatter as yours show.
    Best Regards:
    Baron J.

  3. #3
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    Default

    Micrometers come with test bars, why don't you use them?

  4. #4
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    Quote Originally Posted by tohot View Post
    Micrometers come with test bars, why don't you use them?
    There's no guarantee that the test bars are actually accurate.

    I have seen Mitutoyo test bars that are not within spec.

    So much for Mitutoyo quality.

    Cheers Rob
    The worst that can happen is you will fail.
    But at least you tried.



  5. #5
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    Unless you have a traceable reference standard all the measurements you do are only comparitive .

    By traceable I mean a reference having a NATA endorsed report attached to it.

    Alfclp

  6. #6
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    Quote Originally Posted by nearnexus View Post
    There's no guarantee that the test bars are actually accurate.

    I have seen Mitutoyo test bars that are not within spec.

    So much for Mitutoyo quality.

    Cheers Rob
    What were you comparing the mitu test bars against?

  7. #7
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    Quote Originally Posted by scottyd View Post
    What were you comparing the mitu test bars against?
    Correction - this was on ONE occasion, however it was very noticeable, hence I did the comparison.

    I checked it against several other Mitutoyo and Moore and Wright calibration cylinders/blocks from my other caliper sets.

    It was definitely out of spec (oversize) by a considerable margin - and it was an original/genuine vernier Mitutoyo micrometer, not some cheap clone.
    The worst that can happen is you will fail.
    But at least you tried.



  8. #8
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    Quote Originally Posted by nearnexus View Post
    It was definitely out of spec (oversize) by a considerable margin - and it was an original/genuine vernier Mitutoyo micrometer, not some cheap clone.
    Did you buy the mic new or used Rob?
    Chris

  9. #9
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    Quote Originally Posted by jack620 View Post
    Did you buy the mic new or used Rob?
    Used. From a tool maker I know. Remember, the supplied block is oversized, not undersized from any possible wear. It is also clearly marked as per every other Mitutoyo calibration block I've seen.
    The worst that can happen is you will fail.
    But at least you tried.



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