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A man with 2 micrometers never knows the time

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  • A man with 2 micrometers never knows the time

    I have two 2" mics. I measured a thing with each and got the following:



    and



    Those read differently to me.

    My guess-o-meter, I mean, my dial calipers, says the thing is 1.75"

    Is this normal? How does one adjust a micrometer, and can perma-newbs successfully do it?

  • #2
    Do you have the calibration "standard" ? Mine come with the appropriate length and the small tool to adjust the scale (never needed it). Of course, it needs to read "zero" when at "zero" (easy for a 0-1 mic), and the correct length of the standard (like 1.000). If it can't do both of those things, sell it.

    Mic faces are important. If they are worn it will give the type of small "error" you show. Carbide faces are nice...

    Yours look like a 1-2 inch mic. Put in the 2 inch standard and adjust. Check against the 1 inch standard.
    Last edited by lakeside53; 07-30-2016, 12:16 PM.

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    • #3
      Actually, the FIRST thing to do is adjust it correctly.

      1) check it for play in the spindle. lengthwise shake. Tighten the nut that is hidden under the "thimble", so as to get smooth action with no shake.

      2) Check it for zero and adjust as needed. For a 2", that zero is on a 1" standard.

      3) check it at another point. ideally at 2 or 3 odd places, with gage blocks, but at least with a setting standard.

      4 close it lightly and check for light between the anvils. open it slightly and be sure the line of light is even across the anvils. (assuming you have no optical flat to check with)

      if it does not pass those, get rid of it.

      Your mics are actually not so bad. They are 0,001" graduation, no tenths, and both appear to read basically 1.773. you have no justification for reading closer than the nearest 0.001" with that type mic. The error between them is likely to be in the zeroing. I don't like the way the second one shows up significantly past the mark, though.
      Last edited by J Tiers; 07-30-2016, 12:26 PM.
      CNC machines only go through the motions

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      • #4
        You have two micrometers and a dial caliper. All three give a different dimension and you have no idea which is correct. Probably all three are incorrect, but, for the moment, measure a known standard, not a "thing".

        Comparative measurements with two micrometers can yield slightly different results due to feel and the hold and operation of the barrel. A dial caliper can yield a different measurement for various reasons, chiefly because it sees a different surface that the spot measured by a micrometer.

        If you don't have a proper standard or gage blocks, a bearing will provide a reasonably accurate substitute. They do have +- tolerances, but all three instruments should read the same measurement within that range.
        Last edited by JCHannum; 07-30-2016, 12:45 PM.
        Jim H.

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        • #5
          Tell more us more about the brand and provenance (bought new from reputable source, picked from a dumpster?) of each micrometer. Also, describe or show what was being measured.

          The grads on the second instrument are less appealing to me; the skirt of the thimble has already moved beyond the third line even though the marks on the thimble barrel have not reached zero. Even if this tool is accurate, I would find it more difficult to use because I'd spend more effort verifying the reading and possibly make mistakes.

          For a 2" micrometer, the readings shown appear to me as roughly 1.7728 and 1.7732. A difference of 0.0005 or 1/2 thou. This might be due to inexperience on your part, esp if the object measured introduces any challenges. OTOH, the difference may arise from problems with one or the other mics. As for the reading from the calipers; all other things equal, micrometers are more accurate than calipers.

          More input, please. (and, yes. Micrometers can be checked and calibrated for accuracy.)

          .

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          • #6
            Originally posted by J Tiers View Post
            They are 0,001" graduation, no tenths, and both appear to read basically 1.773.
            Look more closely at the first mic, tenths appear on the barrel.

            .

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            • #7
              Originally posted by J Tiers View Post

              ......They are 0,001" graduation, no tenths, ......
              The first pic clearly shows a tenths micrometer.

              Pete
              1973 SB 10K .
              BenchMaster mill.

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              • #8
                They are indeed 2" mics. The upper mic is an older Japanese micrometer. As I test it against 1" and 2" standards, the standard gets "kicked" a little. Unsurprisingly, it fails Jerry's 4th test. I suppose this mic has been dropped. #mourn

                The other mic, using the same set of standards, feels good, passes test #4 at 1" and 2", and reads "reasonably" at 1" and 2". Of course, the mic still seems out of adjustment per the original image. I do not know if the faces are carbide.



                Now, about adjusting this mic... What we're really talking about is somehow shifting the sleeve a small amount with resepct to the thimble, such that at 1" and 2" the 0 line on the thimble lines up with the longitudinal 0 line on the barrel, and the 0 scale line is split(?) by the edge of the thimble...

                edit - lol same mic, Mine's a SPI, but it's the same. At roughly this point in the video you can see the same gap: https://youtu.be/2Q8cwupE4yE?t=2m29s
                Last edited by Tony Ennis; 07-30-2016, 01:11 PM.

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                • #9
                  https://www.youtube.com/watch?v=bzjBY_QahRA
                  Basically to calibrate mic's you move the barrel in and out by turning the whole cylinder in and out on a fine thread then lock it down. Easy to do and not something you should need to do often. Calibration should remain valid for more than a year and can last for a decade if treated with care.
                  Last edited by SpoonerandForker; 07-30-2016, 01:22 PM.
                  I hear and I forget.
                  I see and I remember.
                  I do and I understand.
                  Confucius (孔夫子)

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                  • #10
                    You hint at inexperience, so don't get excited yet.
                    Not unusual for more than one person reading a "thing" with a mic to get a different value. Guys that work in shops that do somewhat fussy work get their tools run through inspection and more or less develop a similar "feel" to the standard with the mics they use.
                    You personally should have the same "feel" using two or more of your own different tools. "Feel" being the subjective amount of squeeze you apply holding the mic while measuring the part.
                    Let's not talk about calipers of any sort, even though they are an improvement over a tape measure and are quick for rough work. You can verify a caliper against a mic but not vice versa.

                    The "thing" you test your mics against needn't be a mic standard or Jo blocks, but it should have essentially flat parallel ends so you don't introduce diagonal error. All the foregoing posts are salient regarding parallelism of mic faces.
                    If you can't hit the same number with a little practice and adjustment to a standard; the mics are made by reputable makers not abused, they can be relapped and certified. You would have to weigh the benefit vs. new.

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                    • #11
                      Originally posted by EddyCurr View Post
                      Look more closely at the first mic, tenths appear on the barrel.

                      .
                      Yep it do indeed..... but only on the FIRST one..... the second does not show any, and of course, I looked closely only at it...............

                      Sounds like the first one is out of contention anyhow
                      Last edited by J Tiers; 07-30-2016, 01:31 PM.
                      CNC machines only go through the motions

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                      • #12
                        Originally posted by Carm View Post
                        You hint at inexperience
                        Ha, trust me, I am not in denial :-D

                        I probably should make clear the original issue; the 1st mic is showing 1.772+ the 2nd mic is reading 1.798+. I used the dial calipers to sniff-check the answer.

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                        • #13
                          I would read them as 1.7728 and second as 1.7734 remembering that the last digit is questionable. That leaves just 0.0006 or 6 tenths bust which is adequate for most work.
                          I hear and I forget.
                          I see and I remember.
                          I do and I understand.
                          Confucius (孔夫子)

                          Comment


                          • #14
                            Originally posted by EddyCurr View Post
                            Tell more us more about the brand and provenance (bought new from reputable source, picked from a dumpster?) of each micrometer. Also, describe or show what was being measured.

                            The grads on the second instrument are less appealing to me; the skirt of the thimble has already moved beyond the third line even though the marks on the thimble barrel have not reached zero. Even if this tool is accurate, I would find it more difficult to use because I'd spend more effort verifying the reading and possibly make mistakes.
                            This is my issue. I read the SPI as .7 + .075 + .023 + change; the thimble has passed the .075 mark.

                            Originally posted by EddyCurr View Post
                            For a 2" micrometer, the readings shown appear to me as roughly 1.7728 and 1.7732. A difference of 0.0005 or 1/2 thou.
                            .
                            Heavens, I look forward to the day when I can reasonably fret over .0005"

                            I am measuring the hub on a garden-variety spindex so I can make a new plate.

                            The first micrometer is an old Japanese NSK. I acquired it from a retired machinist. The 2nd caliper is a Chi-com SPI I purchased new through Enco (?).

                            Both are 2" micrometers and both measure to .0001. While the 2nd picture (the SPI) doesn't show the tenths, they are there. But I'm not worrying about tenths right now. I'm also not worried right now about proper measuring technique; I think I know how to do it.

                            I'm concerned that the SPI is reading about .022 more than I expected.

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                            • #15
                              It's possible that I simply don't know how to read the micrometer.

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