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Thread: Parallelism Does not Control Form? Question for GD&T Certification Practice Exam

  1. #1
    Associate Engineer
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    Parallelism Does not Control Form? Question for GD&T Certification Practice Exam

    Here's a test question:

    The 0.1 parallelism control will:

    a. limit the flatness of the surface to 0.1

    b. override Rule 1

    c. not control the flatness of the surface

    d. increase the outer boundary to 20.7

    **(This question is referring to a simple plate. Datum A is the base of the plate and parallelism is applied to the top of the plate)

    __________________________________________________ ___

    The correct answer is (c). However, can someone please explain how the answer is not (a)?

    I understand that parallelism is technically not categorized as a "form" control. However, if the surface deviation was to exceed 0.1, then wouldn't that also cause the parallelism to also exceed 0.1? So that, yes this parallelism is controlling the flatness to 0.1.

    If (a.) is an incorrect answer, then does that imply that the flatness can exceed 0.1 but still be parallel within 0.1?

    Someone please explain

  2. #2
    Technical Fellow Kelly_Bramble's Avatar
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    Which dimensioning and tolerancing standard?

    ASME and ISO have different interpretations based on Rule #1 and the Envelope Requirements clauses.

    Also, is the parallelism applied to a surface or feature of size?
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
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    This is for ASME Y14.5M.2.

    It turns out that in the question I was referring to there was actually a tangent modified to the top surface that I missed.

  4. #4
    Technical Fellow Kelly_Bramble's Avatar
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    There is no ASME Y14.5M.2 document or other - you're probable using one of the following

    ANSI Y14.5M-1973
    ANSI Y14.5M-1982
    ASME Y14.5M-1994
    ASME Y14.5-2009
    ASME Y14.5-2018

    You should determine the standard and identify it when asking questions..

    It matters
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

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