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Thread: BAD GD&T conversion

  1. #1

    BAD GD&T conversion

    I have a drawing with bad GD&T. I want to convert it to a "ok" version.
    It is about a 6 holes pattern of 6 H7 mm positioned on a pitch diameter of 25.78 +0.012 - 0.006 mm (the tolerance is asymetrical). The angular placement along the pitch diameter is of 60 +- 0.25 degrees.
    Hole pattern_V01.JPG

    So, I want to convert the pitch diameter and the angle as a "basic".
    The 2 tolerances will need to be converted to a position tolerance, the pitch diameter tolerance and the angular position tolerance.
    Hole pattern_V02.JPG

    What is the proper procedure to convert that?

    Thank you

  2. #2
    Technical Fellow Kelly_Bramble's Avatar
    Join Date
    Feb 2011
    Bold Springs, GA
    To be clear GD&T includes limits tolerances - as shown in your first image. The limit tolerance specifications are correct GD&T.

    To convert the limit tolerances into a GD&T geometric tolerance (Position) change all associated dimensions, angle and Bolt Circle into basic dimensions. Then using an appropriate geometric tolerance for position at the required tolerance (not zero) enter into the feature control frame.

    Not knowing your end item functional requirements I cannot suggest a position tolerance. You can convert the limit tolerances into equivalent positional tolerance if the limit tolerances were functionally correct.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

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