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Thread: Proper way to dimension diameter of cylinder

  1. #1
    Associate Engineer
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    Bang Head Proper way to dimension diameter of cylinder

    I am struggling with the proper way to dimension the diameter of a cylinder.
    The thing that I am most concerned about is that the maximum circumscribed diameter is no larger than 4.5mm.

    The issue that we have had in the past is that we specified a diameter tolerance of 4.5mm +.00/-.125 but, we ended up with a "TRI lobe" shape where the circumscribed diameter was measuring 4.6mm and wouldn't fit in the hole.

    I cant decide if I give a diameter tolerance of 4.38 mm +/-.062 and a circular tolerance of .06mm.

    My head hurts........

  2. #2
    Administrator Kelly Bramble's Avatar
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    What dimensioning and tolerancing standard are you specifying the drawing too? Ever heard of rule #1 (Envelope Principle) for ASME Y14.5?

    Additionally, what is the size specification for the mating part?
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
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    Yes, I am dimensioning to Y14.5. The mating part has a tolerance of 4.51mm +.125/-.000.
    I understand the Envelope Principle but, I am trying to figure out a way to specify the tolerance we need in GD&T terms.
    Maybe I am over thinking it.
    The past problem can not be detected using a standard two point measuring system, i.e. Micrometer or calipers.

  4. #4
    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by clint_clark View Post
    Yes, I am dimensioning to Y14.5. The mating part has a tolerance of 4.51mm +.125/-.000.
    I understand the Envelope Principle but, I am trying to figure out a way to specify the tolerance we need in GD&T terms.
    Maybe I am over thinking it.
    The past problem can not be detected using a standard two point measuring system, i.e. Micrometer or calipers.
    The envelope principle (Rule #1) is invoked by default when ANSI or ASME Y14.5 is declared on the engineering drawing. Rule #1 and limit tolerances are very much GD&T specifications. GD&T is not just the geometric characteristics (flatness, perpendicularity, etc..). The idea that limit tolerances are not GD&T (+/-) is an incorrect assumption.

    Manufacturing and quality should be building the hole and mating pin such that the requirements of Rule #1 (3D boundary of perfect perfect at MMC).

    You likely have both a manufacturing and quality problem..
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

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