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Thread: How to interpret stacked basics from feature

  1. #1
    Associate Engineer
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    How to interpret stacked basics from feature


    My question is if the position location to the 2X Ø.126 holes are affected by the movement of the Ø.281 hole the [.150] basic comes off of?
    The customer says no. I am to interpret the position to the 2x .126 holes as a stack of the [3.563] basic and the [.150] basic. The movement of the Ø.281 hole is not applicable.
    Is that kosher?
    I would think that the proper method would be to place a basic of [3.413] to the two holes if that was the intent.

    Is there a section in the GD&T book that would clarify this?

    note: a FCF for the 2x .126 holes exists in a detail not shown in the above view
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  2. #2
    Technical Fellow Kelly_Bramble's Avatar
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    My question is if the position location to the 2X Ø.126 holes are affected by the movement of the Ø.281 hole the [.150] basic comes off of?


    They are not... The
    2X Ø.126 holes are probably related to whatever the datums are specified within the associated feature control frame.

    The
    Ø.281 hole can move all over within the specified tolerance as it is related to the specified datums..

    Basic dimensions are considered tolerance-less.

    Can you post the complete specification for both hole features?
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
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    Thanks much.
    Any clue where in the GD&T standard I might find that clarification?
    Thanks much.
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  4. #4
    The only datum I see called out on the views that you provided is datum B, which seems to be coming from a reference dimension (illegal). I will assume that datum A is a mating surface and datum B comes from the center hole. I will also assume that there is some datum C that clocks the part. The 2x .126 holes are positioned to datums A, B, C. Datums A, B, C establish the datum reference frame, which is three mutually perpendicular planes that yield the origin of measurement. The 2x .126 holes should be basically dimensioned from this origin. It appears that this has been done ([3.448] & [.395)]. So, no matter what size the center hole has been produced at the origin of measurement will not move. The 2x .126 holes are not measured from the .281 hole, they are measured from the datum reference frame.


    This is assuming that I interpreted your question correctly.

    ASME 2009 standard - chapter 7.

    ASME 1994 standard - chapter 5.

  5. #5
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    Yep.
    That answers all my questions.
    Thanks much!

  6. #6
    Technical Fellow Kelly_Bramble's Avatar
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    The only datum I see called out on the views that you provided is datum B, which seems to be coming from a reference dimension (illegal).


    There nothing "
    illegal" about a datum being derived from a feature defined with a reference dimension.. In the example given it is perfectly legitimate.

    I would add Chapter 3 and mostly Chapter 1..
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

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