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Thread: applying significant digits to a geo tolerance in a feature control frame

  1. #1
    Associate Engineer
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    applying significant digits to a geo tolerance in a feature control frame

    If I have a feature control frame with regards to flatness, and the geometric tolerance is to .001", do you still apply significant digits to that number?

    Ie. my mech insp. measures the part, and comes up with a flatness of .0013", is that within tolerance, because it is to 3 significant digits and .0013 rounds down to .001?

    -Or- because it is in the box it is a drop dead number, maximum, so .0010000001" technically is out of tolerance?

    I have read that the geometric tolerance is total, not a +/-, but this isn't really talking about that.

    This has come up before at work, and we are still not exactly sure, so if you could point to where it mentions that in the standard, I would appreciate it. I am ok if it is a common knowledge thing too.

    Thanks,
    JimL

  2. #2
    Administrator Kelly Bramble's Avatar
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    ASME, ISO or whatever...

    Tolerances are not rounded. Flatness .001 = .0010000000000000000000000000000000000..... infinity

    Your metrology equipment should be 10X more repeatable for imperial units and 5X for SI.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
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    Ok, so are you saying all tolerances are not rounded, or just the tolerancing in a control frame? Also, could you point this out in the standard?
    I am going to have to argue my case.
    Thanks,
    JimL

  4. #4
    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by jamesl View Post
    Ok, so are you saying all tolerances are not rounded, or just the tolerancing in a control frame? Also, could you point this out in the standard?
    I am going to have to argue my case.
    Thanks,
    JimL
    '

    ASME Y14.5-2009, Paragraph 2.4 "Interpretation of Limits"

    limits.png

    This is very-very basic knowledge, your organization needs training ASAP.

    See:

    https://www.engineersedge.com/GDT_Training.htm
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  5. #5
    Administrator Kelly Bramble's Avatar
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    Also, ASME Y14.5-2018, Paragraph 5.4.

    and

    ASME Y14.5M-1994, paragraph 2.4

    and

    ANSI Y14.5M-1982, paragraph 2.4

    and

    ANSI Y14.5-1973, paragraph 2.4

    and

    ANSI Y14.5M-1966, Section 1

    Identical text as ASME Y14.5-2009
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  6. #6
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    Kelly,
    Thank you so much for your time, I appreciate it.
    JimL

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