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Thread: Straightness of Feature of Size Override Rule #1

  1. #1
    Associate Engineer
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    Straightness of Feature of Size Override Rule #1

    Can you someone share an example where straightness or flatness can override Rule #1?

    For example, say we have a shaft with limit tolerances of 12.7 to 12.2 and straightness tolerance of 0.02.

    Is the straightness tolerance overriding Rule #1 and allowing a straightness deviation at MMC? Therefore, causing the virtual condition to increase to 12.72? I'm pretty sure this is not correct and that the V.C. does not increase to 12.72. But then how does straightness override Rule #1?
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  2. #2
    Technical Fellow Kelly_Bramble's Avatar
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    Example 01 "A' the straightness tolerance is applied to the cylinder surface (feature without size) therefore Rule #1 is applicable.

    Example 01 "B" the feature control frame is associated with the size specification therefore the straightness is applied to the Feature of Size (FOS) and the tolerance is applicable to the derived center line and Rule #1 does NOT apply.

    See ASME Y14.5-2009, Figure 5-2 or Figure 5-3

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  3. #3
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    It's actually in preparation to take the GD&T certification exam through ASME. There are sooo many nuances to understand.

  4. #4
    Technical Fellow Kelly_Bramble's Avatar
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    Quote Originally Posted by armand_matossian View Post
    It's actually in preparation to take the GD&T certification exam through ASME. There are sooo many nuances to understand.
    I'm certified at the Senior GDTP level since 1997 - look me up (GDTP-S-150).
    Search here: https://asme.learningbuilder.com/Pub...rSearch/Search

    Advice, study the standard you're testing for - read every page many-many times and memorize everything. You'll need to have a fluent understanding with the standard you're preparing for.

    "There are sooo many nuances to understand." Yes, there is - and I suspect you're not ready for the test based on the that statement.

    Good luck
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

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