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Adjusting outside mic's

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  • Adjusting outside mic's

    I have a Polish made 0-4" micrometer set that I bought from Enco. They came with 1,2, and 3" steel pins that I assume are standards. There's also a couple of funky looking hooks that I assume are adjustment wrenches.

    These are my first mic's and I want to set them up as best they can be. No instructions came with them, so I'm just guessing on how to proceed. What I've discovered so far is that after taking the end cap off, there's an Allen screw on the side. Loosening that allows the barrel to be positioned anywhere I want. Seems rather crude, and I've no clue what the little hook-wrench is for.

    There must be a real procedure for this... can anyone explain?

    And oh yeah, how close can I exect those steel pins to be?


  • #2
    The "hook-wrench" is a spanner for adjusting the barrel to coincide with the thimble. Opposite the set screw there should be a hole in the barrel for the pin on the spanner to fit into. If not the set screw hole could serve this purpose. I am guessing the thimble is what you are calling the "end cap". Set a standard, say a 2", between the anvil and the end of the barrel. Use the mic to "measure" the standard. If it a ratchet type, use the ratchet wheel. When the ratchet wheel stops, look at the barrel/thimble markings. "0" on the barrel should be in line with "0" on the thimble. If not then loosen the screw, then using the spanner, spin the barrel to coincide with the thimble. Tighten the set screw. Calibration of instruments is "supposed" to be done in controlled conditions. Probably not possible in the home environment. Make sure everything is CLEAN before you start, including the area you are "calibrating" in. How close are the standards? Depends, they could be over/under. The only way to determine the true length of the standards, is to measure them against a known standard in the same conditions. Are the mic's graduated to .001 or .0001"?
    Paying Attention Is Not That Expensive.


    • #3
      A standard mic is adjusted as follows. On the mic barrel (were you read the mic) near the frame should be a small hole. You use the standard or on the 0-1" mic just close it all the way (clean the jaws first, to attain an accurate reading). When closed or using a standard, attain the proper "feel" and observe the reading, it should be "zero". If not, use that spanner type wrench with the little "point" inserted into the small hole to turn the spindle to read "zero". Normally, once it's set, it should be good for years. You mentioned you took the back cap off. I think you mean the "barrel", while off you should see a round "nut" with holes around the outside diameter. This is used to adjust the tightness of turning the barrel and take up any "freeplay". If needed, adjust this first, then zero it out. But, normally you should never have to adjust this. Once it's set at the factory, it should be good for many years!. -- A standard should be accurate to a "tenth" of a thousandth of an inch or better, depending on quality. But, for all practical purposes should be more than accurate for all but the most exacting jobs.

      [This message has been edited by Jim Luck (edited 03-07-2005).]


      • #4
        The steel pins are your setting standards. The only way to know is to compare your standards to something of known certified length. Gage blocks are generally used as length masters. Here's a short article:

        Every brand of micrometer uses a different method to calibrate. My Polish set (VIS brand) as well as my Brown & Sharpe, Mitutoyo, and Fowler mikes are adjusted by inserting the pin on the hook wrench & rotating the barrel until zero is indicated. There are other methods used and yours may adjust differently.
        Barry Milton


        • #5
          One note, I do not use the friction or rachet feature on any mic I use. They are very inconsistent. On the Polish mic I have the friction thimble has to be broken loose if I were to use it and even then it changes as I rotate it. The rachet types can have a differant "feel" between two of the very same make and model of mic.

          Learn to tighten the mic by feel rather than using the friction or rachet and you will find your readings to be more accurate and consistant.



          • #6
            Like I and, topct said, you must attain the "feel" -- (through practice!). Unless your using indicating mic's, nothing can replace the human touch. A buddy of mine uses his ratchet/friction stops and I just look and shake my head, but he thinks he's right, whereas I know I'm right. Great to know your willing to learn, in time, you'll be the judge!!!. ---