Setting up to datums

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  • Setting up to datums

    I am having a issue again with engineering, my problem is that they are trying to set up a datum scheme and set everything to A/B/C. This is fine but they want the origin to be to B and they are drawing all the prints like this now. I have always been taught the if the alignment is to A/B/C, you would level to A (plane), assuming B and C are two holes i would rotate between B and C, and that i would origin to C. Were my teachings correct or not? I have read briefly read through the AMSE standards to prove one way or another and havent really found anything. So i was hoping someone out there can shed some light on this. Thanks in advance.

  • #2
    That is one way to do it but there are many many different ways. It all depends on the part.
    Saving the world, one bad part at a time.

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    • #3
      Thanks for the fast response. My only concern is that if they do a profile from A/B/C, or a true position from A/B/C, and they are origined on B that it would be incorrect. Again i have been taught whether right or wrong that you would go from left to right and for either of those examples that you would be origined on C, and they want to origin on B.

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      • #4
        I have seen it done several ways:
        Using B and C to rotate (orient) with B the origin in one axis and C the origin in another.
        Using B and C to rotate (orient) and B the origin in 2 axes.
        Using B and C to rotate (orient) and C the origin in 2 axes.

        It works for me as long as it is clear where the origin for all 3 axes are supposed to be.
        If it is not clear, then I choose.
        It helps to have CAD with the orientation and origin established, then there is no doubt.
        Lately, it occurs to me
        What a long, strange trip it's been.

        2017 R1 (Offline programming)

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        • #5
          So matt you would really only use C as rotational in this instance? I was under the impression C would be the 2-axis origin and be would be just part or the rotation?

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          • #6
            Thank you all for your help, its good to see that there are alot of different ways that people do this. So more or less it comes down to what engineering wants? I always thought that ASME standard stated that it had to be one way or another, but after reading through it (briefly) that it really doesnt.

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            • #7
              Where is the (x or y) origins on the print? If -b- is shown as the (x or y) origin(s) then -b- should be set as the (x or y) origin(s).

              B&S CHAMELEON/PCDMIS CAD++ V2011

              There are no bugs, only "UNDOCUMENTED ENHANCEMENTS!"

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              • #8
                I agree dhp, i just didnt think it was correct to origin B if the callouts were to ABC. I was always taught to origin C in one or both axis. I wouldnt have thought it would have been correct, but the by the sounds of it they are ok to do that. Which is fine with me but i wanted to make sure. Thanks for the help guys.

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                • #9
                  Originally posted by dph51 View Post
                  Where is the (x or y) origins on the print? If -b- is shown as the (x or y) origin(s) then -b- should be set as the (x or y) origin(s).
                  +1

                  I always rotate from location in the order that features are datumed to. If necessary... re-datum to satisfy the engineering types.
                  sigpic
                  I am fluent in three languages:
                  English, Sarcasm & Profanity.

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                  • #10
                    Thanks to all of you. Its good to see that i wasnt totally wrong, its just that there are more then one way to do it and if the print and cad are coming from B then origin from B. I was just afraid by doing so would be incorrect when doing a profile or a tp to ABC since i always looked at it as though it should be origined to C.

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                    • #11
                      Is there anyone else that see it this way? Just curious? So if they have the origin at B and the TP calls from ABC would it be incorrect to do the callout with B as the origin per ASME standards?

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                      • #12
                        Originally posted by oriental_sun View Post
                        Is there anyone else that see it this way? Just curious? So if they have the origin at B and the TP calls from ABC would it be incorrect to do the callout with B as the origin per ASME standards?
                        Here is an example from tec-ease that shows C used as an orienting feature only and not as an origin:

                        http://www.tec-ease.com/gdt-tips-view.php?q=243

                        And here is a pic in case the link won't work for ya:

                        Lately, it occurs to me
                        What a long, strange trip it's been.

                        2017 R1 (Offline programming)

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                        • #13
                          Originally posted by John Riggins View Post
                          Here is an example from tec-ease that shows C used as an orienting feature only and not as an origin:

                          http://www.tec-ease.com/gdt-tips-view.php?q=243

                          And here is a pic in case the link won't work for ya:

                          [ATTACH=CONFIG]6441[/ATTACH]
                          Excellent!
                          sigpic
                          I am fluent in three languages:
                          English, Sarcasm & Profanity.

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                          • #14
                            Thanks John

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                            • #15
                              LMAO on this one. A lot of our medical prints from OEMs have the datums so mucked up. They will call the primary C, the secondary A and the tertiary B. You can them anything you want as long as the DRF for the specific feature being toleranced is constructed correctly. Many of us have drawing that have 5 DRFs or more depending on the application of any specific feature and how the engineer thinks he wants it done.
                              Xcel & MicroVal Pfx & Global 37mr4 thru 2012mr1sp3
                              Contura Calypso 5.4

                              Lord, keep Your arm around my shoulder and Your hand over my mouth. Amen.

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