Starrett Dial Calipers - Not Zeroing, .025" Off
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  1. #1
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    Default Starrett Dial Calipers - Not Zeroing, .025" Off

    I have a newer Starrett 6" dial caliper, hardly used, that is now reading off by .025". I don't recall any major impact or event that would have caused this.

    Any thoughts on what would cause this and how to fix it?

    • The jaws close without any visible gap - certainly not .025"
    • The rack gear appears to be free of any debris
    • It was bought new, stored in a case with a gap between the jaws
    • I also noticed the dial adjustment turns very hard - but since you typically only move it +/- a few thou, I may have just never noticed this is the norm for this particular caliper


    My next step is to just take it apart.

    Thanks

  2. #2
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    The pinion has likely jumped one tooth on the rack. Sometimes one can insert a shim to get it back. If this
    the cause then mostly that happens because of a chip getting wedged in the rack.

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    Quote Originally Posted by RCasey View Post
    My next step is to just take it apart.
    Follow him in this video.

    YouTube

    I wouldn't touch a dial caliper with a barge pole but, as the guy in the video says, it's a personal choice.

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    I agree with Jim Rozen's analysis. I have never had this happen with my Starrett calipers (.100"/rev) but it's more common with some older Mitutoyo calipers I have (.200"/rev). When that occurs, it's usually about .020" per gear tooth. And, most likely to happen when the calipers are around during a lot of chip generation and measuring frequently at the machine.

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    I tend to use mit. digimatics at work but honestly I do have a 'thing' for starrett dial calipers, just like the feel. Also
    it doesn't lie to you and tell you there's half tenth accuracy there.

    So I've gotten pretty good at taking them apart to clean them. No matter how careful you are there's always
    a bit of gunk in the rack that has to be brushed out. If it's a solid chip that gets jammed in there, the pinion will
    hop a tooth. Unless its a real obvious one-off the best bet is indeed to strip it down and give it a good cleaning.

    Helps if you have a microscope to do the fiddly bits, also the first time you dismantle one, do it in a large flat
    cardboard box to catch the stuff you would otherwise drop on the floor.

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    Maybe informative.

    YouTube

    He does get one thing wrong or maybe just doesn't know.

    There is a manufacturing specification for calipers that includes vernier, dial and digital. In that spec are also the specified tolerances for accuracy.

    For internal, step and depth measurement there is an extra 0.02mm (0.001") over and above that on the external jaws.

    I don't know what is specified in the USA for caliper accuracy but in the rest of the world then all caliper manufacturers that specify the manufacturing spec (including Mitutoyo) give the following spec and thus the tolerances.

    No need to go further than page 1-4.

    http://www.f-m-s.dk/DIN862.pdf

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    I used a B&S digital 99% of the time. I have several digital of different brands, but I love my old B&S dial calipers. I think I'm going to be buried with them!

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    Quote Originally Posted by crazygoat View Post
    I used a B&S digital 99% of the time. I have several digital of different brands, but I love my old B&S dial calipers. I think I'm going to be buried with them!
    Still have my first pair of mitutoyo four inch calipers, bought them used years ago. I've had them apart probably five
    or ten times over the years, at this point they're my outdoor measuring items in the garage shop. Still good for maybe
    +/- three thou, good for a quick check without having to get the good ones from inside.

    The digimatics are bullet proof, one shop I worked at put the new ones on the lathes, from there they went to the
    milling machine, from there they went to the planer, from there to the circular saw, and then from there to the
    kasto cutoff saw. They were still good to a couple of thou at the end though, even after years of (ab) use.

  10. #9
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    I find it hard to believe that re-zeroing a dial caliper is such a lost art.


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