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Thread: Can 3 square holes in an L formation be called out as Datum B?

  1. #1
    Associate Engineer
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    Confused Can 3 square holes in an L formation be called out as Datum B?

    Is Datum B valid?
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  2. #2
    Administrator Kelly Bramble's Avatar
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    Technically, yes... The specification doesn't actually specify the three square hole - only the two surfaces which the dimension extension lines are attached to..
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
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    No it states 6x or six times and this is how our customer interpretation of it. I can see two but I cant see three. How would one align it? Best fit? Even at best fit I do not feel its a valid datum callout.

  4. #4
    Administrator Kelly Bramble's Avatar
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    Referring to ASME Y14.5-2009 standard, paragraph 7.4.5.1 and figures 7-28, 7-29, 7-30, 7-31 and 7-34. Additionally, my book Geometric Boundaries I & II per. ASME Y14.5-2009, pages 7.20 - 7-22..

    Datum "B" specifies that the three (3) square features of size are used to establish the datum. There are three (3) tolerance boundaries at 0.6 x 0.6 mm at MMB which are used simultaneously to establish that datum feature. One could use a fixture with three square pillars at MMB size located at the specified Basic dimensions to simulate the datum for verification or a CMM.

    The datum specification is valid..
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  5. #5
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    Thank you for the clarification Kelly.

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