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Thread: Datums call out @ part center is correct?

  1. #1
    Associate Engineer
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    Datums call out @ part center is correct?

    Can I use part center to call out datums?. Please see the image attached.

    Thanks,
    Darshan
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  2. #2
    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by bt.darshan View Post
    Can I use part center to call out datums?. Please see the image attached.

    Thanks,
    Darshan
    NO!

    Datum symbols may NOT be applied to center lines, center planes, or axes.

    ASME and ANSI explicitly state this rule.

    References:

    ASME Y14.5-2009, para. 4.8.2 (page 57)

    ANSI Y14.5M-1994, para 4.3.2 (page 52)

    When measuring parts a datum is established from a physical feature not an imaginary center line. A physical feature must be identified as the datum to establish a physical datum origin.
    Last edited by Kelly Bramble; 08-05-2014 at 07:59 PM.

  3. #3
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    Thanks Kelly...

  4. #4
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    Quote Originally Posted by Kelly Bramble View Post
    NO!

    Datum symbols may NOT be applied to center lines, center planes, or axes.

    ASME and ANSI explicitly state this rule.

    References:

    ASME Y14.5-2009, para. 4.8.2 (page 57)

    ASME Y14.5M-1994, para 4.3.2 (page 52)

    When measuring parts a datum is established from a physical feature not an imaginary center line. A physical feature must be identified as the datum to establish a physical datum origin.
    Hi Kelly,

    Is there way to justify & get the excuse to update it if it’s wrong. Please advise

  5. #5
    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by bt.darshan View Post
    Hi Kelly,

    Is there way to justify & get the excuse to update it if it’s wrong. Please advise
    Short answers:

    Because it is undefined and "wrong"?

    Look, to measure from a datum feature one has to know what that datum feature is. When a datum is attached to a center line the physical datum feature is UNKNOWN. What inspection or manufacturing utilizes to establish that datum is random. Engineering or design needs to be specific with regards to what feature is used to establish the datum origin from which measurements are made.

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