True Postion

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  • True Postion

    I am still trying to figure out this true postion stuff. I hav a square part that is 3.8in long by 1.4 in wide. There are two circle spaced 1.88 apart. I have a true postion callout I think. The 1.88 dim is basic. In the GD&T box there is o circle with crosshair then .030 dia. Thats it.

    Couls someone explain this to me. What am I checking.
    Thanks in advance
    B. Jacobs
    B&S Global 12.15.10
    2014.1

  • #2
    Here is a sketch that might help
    Last edited by B. Jacobs; 04-02-2008, 09:24 AM.
    B. Jacobs
    B&S Global 12.15.10
    2014.1

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    • #3
      Is there a DRF (datum reference frame) ref at the end of the feature control frame (FCF)?
      Are there datums identified on your drawing?
      1 last thing, could you post a more detailed pic of the drawing?
      Thanks,
      Kevin
      RFS Means Really Fussy Stuff

      When all you have is a hammer - everything looks like a nail....
      sigpic

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      • #4
        This is what it looks like. Unfortunitly thats it. I drew the best I could. Hope this helps.
        Last edited by B. Jacobs; 04-02-2008, 09:24 AM.
        B. Jacobs
        B&S Global 12.15.10
        2014.1

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        • #5
          the way i would check it is to align the 2 dias to each other. origin 1 dia. and check the 1.880 dim. theres not much more to the sketch. basically you have a 1.880 +/-.015 dimension
          sigpic
          Southern Man don't need him around anyhow!

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          • #6
            I agree with George. Align using the 2 diameters, Origin on 1 diameter and report the other one. You could than use your position tolerance and answer the TP call out X=0 Y=1.880. Or a down and dirty way to do it is check the distance between the two diameters and double the difference of your measured from the basic and you will get your true position answer.


            BS
            Windows 7
            Pc-Dmis 2015
            Global Performance 7-10-7


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            • #7
              This is a definate case where the person who drew and toleranced this part knows that GD&T exists but DOES NOT know how to apply it to a drawing.

              myself, I would align off the two "zero" sides of the block, pick up the holes and apply the TP callout.

              TP of .030" is pretty wide open anyways, unless this is in mm and then its a wee bit tighter....

              bob
              Which one gets ridden today? MPH vs MPG..tough choice, both are FUN
              sigpic

              Starrett RGDC 4028-24 :alien:
              Demon vintages 3.7, 4.1, 4.2, 4.3, 2009

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              • #8
                I agree with George as well. Word for word.

                TK
                sigpicHave a homebrew

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                • #9
                  I did what Goerge said I think. Here is my alignment.

                  =ALIGNMENT/START,RECALLCC-ALN, LIST= YES
                  ALIGNMENT/LEVEL,ZPLUS,CIR1
                  ALIGNMENT/ROTATE,YPLUS,TO,CIR1,ABOUT,ZPLUS
                  ALIGNMENT/TRANS,XAXIS,CIR1
                  ALIGNMENT/TRANS,YAXIS,CIR1
                  ALIGNMENT/TRANS,ZAXIS,CIR1
                  ALIGNMENT/ROTATE,YPLUS,TO,LIN4,ABOUT,ZPLUS
                  ALIGNMENT/END

                  This seemed to get the answers I was looking for. Now I am doing TP to circle two. By the way Cir1 is the top cir. and line 4 is right side of part.
                  B. Jacobs
                  B&S Global 12.15.10
                  2014.1

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                  • #10
                    email me with your phone # if you'd like, it'll take about 3 minutes to walk you through this.

                    TK

                    [email protected]
                    sigpicHave a homebrew

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                    • #11
                      Like all have said, not the best use of TP. Typical, but wrong.
                      When in doubt, post code. A second set of eyes might see something you missed.
                      sigpic

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                      • #12
                        I was just given another one. I wish they knew how to do these TP things. This time it is 4 holes. Same GD&T box as before but instead of .030 it is now .014. I am trying all sorts of things.
                        B. Jacobs
                        B&S Global 12.15.10
                        2014.1

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                        • #13
                          Is there a block in the corner that says reference X|Y|Z unless otherwise specified and/or datums called out on the drawing anywhere? Quite a few of the drawings I get have the "block tolerance" application. Dang lazy design engineers.

                          Jaime
                          sigpicYou're just jealous the voices talk to me.

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                          • #14
                            Get the ASME Y14.5-1994 Dimensioning and Tolerancing Book. Maybe an engineer in your company may have it. Or get Geo-Metrics by Lowell W. Foster.
                            It is a book for the application of GD&T techiques


                            BS
                            Windows 7
                            Pc-Dmis 2015
                            Global Performance 7-10-7


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                            • #15
                              I'd take it back to Engineering and ask what my datums are. Where is X,Y,Z zero point. That is where all the measuring should start from. A drawing is supposed to communicate the Engineer/Customer needs. Give'em what they ask for , prove it, then show them the "proper" way to ask for it.
                              When in doubt, post code. A second set of eyes might see something you missed.
                              sigpic

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