GD&T misunderstanding.

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  • GD&T misunderstanding.

    DSCN1184.jpg
    with very little GDT skill I am having trouble setting this datum structure...my interpret is diff from both my boss and the engineer.
    anyone want to clue me in?
    it was good yesterday, why are you bothering me TODAY?

  • #2
    engineer(new guy) says D is a plane ,I see it as a mid from the 2x.319/.339
    BUT I admit my understandingof GDT has ALOT of room to grow.
    it was good yesterday, why are you bothering me TODAY?

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    • #3
      -D- is a diameter.... or rather the 2 diameters equaling 1 line...

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      • #4
        Ask the engineer how many points make a plane.

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        • #5
          All three center lines of the diameters are on datum D, which is taken from the top-most diameter in the picture. The second diamter down is also toleranced to the same call out ( +/-0.6 from datum A - assuming that is left-side of part in picture) in the box as the first, the third diameter (bottom) is NOT toleranced to that callout.

          Slap that engineer. Then go to "off-topic" and read that thread.

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          • #6
            Originally posted by thesecretpresident View Post
            engineer(new guy) says D is a plane ,I see it as a mid from the 2x.319/.339
            BUT I admit my understandingof GDT has ALOT of room to grow.
            I would concur with the way you are seeing it.
            a midpoint between the upper and lower .319/.339 holes. Note the referenced callout/arrow (-D-).
            the engineer needs to be slapped with a trout... but I DO like the way they spelled 'GAUGE' and 'GUAGE'. Obviously playing both sides of the street in lieu leiu of a spell check....
            but so it goes... (in fact, today...our head of document control thanked us for our 'patients' while Agile was down)

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            • #7
              D is intended to be a theoretical axis mid way between the top and bottom hole. The draftsman obviously understood that the intent could be a bit confusing so they kindly pointed to the theoretical datum and labeled it "(-D-)".
              2013MR1 SP6
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              • #8
                ok,trout slap it is.

                now to start the "dance of interpretation"
                thank you all for your answers.
                it was good yesterday, why are you bothering me TODAY?

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                • #9
                  still struggling.
                  D is shown @ .105 from center cyl.736/cyl.946.
                  so would I create a generic cyl offset from mid of cyl.736/cyl.946?
                  it has got to be easier than I'm trying to make it.
                  it was good yesterday, why are you bothering me TODAY?

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                  • #10
                    Originally posted by ClayT
                    See if this helps clarify things...
                    http://www.tec-ease.com/gdt-tips-view.php?q=202
                    That's a good piece of info, I saved that link to my files to refer back to it for Datum help myself. Thanks for posting that.
                    sigpic "Marine" ... a title that is earned by few........never given.

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                    • #11
                      Originally posted by thesecretpresident View Post
                      ok,trout slap it is.

                      now to start the "dance of interpretation"
                      thank you all for your answers.
                      GD&T is not a cultural language with subtle flavors of interpretation to be danced around.
                      GD&T is a scientific shorthand code with precise definitions to be applied to industrial work.
                      The Standard is the de-coder.

                      Your engineer can actually be commended for thinking in 3D, not all have that skill.
                      I would hazard a guess that he is picturing a plane passing through both theoretically perfect D cylinder centerlines.
                      Explain to him that in measured data it's not likely that those actual centerlines will lie on the same plane.


                      Originally posted by thesecretpresident View Post
                      still struggling.
                      D is shown @ .105 from center cyl.736/cyl.946.
                      so would I create a generic cyl offset from mid of cyl.736/cyl.946?
                      it has got to be easier than I'm trying to make it.
                      Try constructing a 3D line that is the MID of the two D cylinders.

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                      • #12
                        First, the call out for the position of Datum [-D-] is somewhat bogus. If the intent is to truly control the position of the diameter, you need three Datums in the FCF. Otherwise, you are not eliminating all 6 degrees of freedom. Also, you wouldn’t have a tolerance of (.000). Furthermore, without seeing the rest of the print, I can't determine the Datum scheme. Is there a Datum [-A-], Datum [-B-] & Datum [-C-]? With this call out the designer/engineer may be just asking for perpendicularity. Too often I see this call out when what they really want is perpendicularity. If you could provide more information I could better lead you in the right direction.
                        Last edited by mdobb829; 05-01-2013, 02:19 PM.
                        Marty Dobson
                        Director of Quality
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                        • #13
                          my datum A is the milled surface the holes go through.
                          there is no datum B or C.
                          datum d is indicated at .105 from center hole..so it isn't a mid between, unless it is an offset.
                          even a plane between 1.096 and 2.139 would not fall on callout datum D.
                          the gauge line A reffed @ F is a coin distance, NOT my datum A.
                          it was good yesterday, why are you bothering me TODAY?

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                          • #14
                            [QUOTE=Josh Carpenter;352714]
                            GD&T is not a cultural language with subtle flavors of interpretation to be danced around.
                            GD&T is a scientific shorthand code with precise definitions to be applied to industrial work.
                            The Standard is the de-coder.


                            looks good on paper, at a company that is going through it's "break in" period with GDT....it SEEMS like dancing.
                            I keep hearing "that's what we always done"....
                            as the guy with the pcdimis I am trying to be SURE what I do is right, regardless of "what we always done"
                            it was good yesterday, why are you bothering me TODAY?

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                            • #15
                              ok, looks like creating a "set" from the upper and lower .329 holes made the datum D location.
                              I am able to create FCF as per print.
                              THANKS for the help.
                              it was good yesterday, why are you bothering me TODAY?

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