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Zeroing Central Tool Micrometer (NOT H.F.)

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  • Zeroing Central Tool Micrometer (NOT H.F.)

    I have a Central Tool (Auburn, R.I.) mike made for small parts (think watch parts) that I got as part of an estate purchase. It was off zero by half a thousandth, and I wanted it to be right. The guys in my company cal lab fiddled with it, but it was still off by one half a thousandth (but in the opposite direction) afterwards so I ended up monkeying with it myself.

    As it turns out, the secret is simple once you know it.

    Most mikes I think use a collar with the markings on it, and you zero it by turning the markings by turning the end cap. On this particular mike, you have to loosen the cap, which loosens a sort of collet arrangement on the thimble. This is what grips the plunger which has the actual measuring face on the end. So, once you remove the cap, you can push the plunger in a bit, lightly tighten the cap, and turn the thimble in to zero, which pushes the plunger in as you turn the thimble. Once the marks read zero, you can tighten the cap, then back off the thimble and recheck.

    This might be common, but it's the first time I've seen this setup myself. I didn't understand it myself until I took it apart (a common lament, I must say)....and apparently it stumped the guys in the cal lab too. It's now dead nuts on zero (now to get the calibration checked)

  • #2
    Micrometer calibration and certification

    Interesting post - food for thought.

    Some links -not necessarily complete or representative - but from an initial "Google" search.

    This is a good read.

    As are these:

    You can go nuts if you take this to the n^th degree - just be sensible and keep a grip on practicality and reality.


    • #3
      isn't that the same basic system as on some Browne & Sharpe?

      Whoever's it is, I don't like it at all, as most of them I have seen have the cap corroded onto the "collet" area, meaning that you need to apply a lot more force than I like to use with a mic......

      Keep eye on ball.
      Hashim Khan


      • #4
        lt could be like some others, but first I've seen...

        I don't have any Browne and Sharpe, so the mechanism may not be anything unique, but it it the first time I have encountered this setup.

        Certainly the whole calibration scene can drive you nuts :-) However, I was happy to discover the secret of adjusting this thing. Next stop is a stack of gage blocks...I can deal with known errors, but not getting zero at zero is a bad starting point

        What makes this guy special is that it has an extended anvil with a narrow neck as well as a spindle that has a narrow neck. Not something I can get from MSC or McMaster (I don't think..)

        I'd like to post pix but don't have a host yet, though am working on it. Might save someone some hassle.

        Thanks for the remarks.


        • #5
          Originally posted by oldtiffie
          Interesting post - food for thought.

          Some links -not necessarily complete or representative - but from an initial "Google" search.

          This is a good read.

          Having just bought a 3"-4" Mitutoyo micrometer from eBay for $20(!), those links are helpful.

          Have any of you used a metrology service for checking/calibrating calipers or mics?