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Thread: Interpretation of DRF

  1. #1
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    Interpretation of DRF

    I believe the DRF in the attached screenshots is fully constrained thru the Datum A Cylinder and Datum B Cylinders, thus leaving Datum C to do nothing. However, if there is an interpretation of ASME Y14.5-1994, I would love to hear it.

    The function of the part is as follows: the part rotates into position about the A axis, then 2 pins eject from the mating part into the B diameters.

    All un-dimensioned surfaces have a profile to ABC.

    Thanks in advance....
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  2. #2
    Administrator Kelly Bramble's Avatar
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    "thus leaving Datum C to do nothing. " - Except for an undimensioned feature which is tolerance controlled to a Profile A (primary), B (Secondary) and C (Tertiary).

    The note (Profile) could be improved... e.g.

    All untoleranced features shall be dimensionally controlled to a Profile of Surface
    A (primary), B (Secondary) and C (Tertiary).
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
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    Thx. The actual note on the drawing states this, but this was not the question. Iím looking for confirmation that C has no affect on the datum structure because A and B control all 6 degrees of freedom.
    Last edited by tomoakes; 01-31-2021 at 07:37 AM.

  4. #4
    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by tomoakes View Post
    Thx. The actual note on the drawing states this, but this was not the question. I’m looking for confirmation that C has no affect on the datum structure because A and B control all 6 degrees of freedom.
    ASME Y14.5-1994, paragraph 4.5.8 and associated graphics Figure 4-22.

    Yes, datum A and B could be used to define and create/control lockdown of all six degrees of freedom. However, due to common confusion I don't recommend this practice.

    Key words "when part function dictates".
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