True pos. one axis.

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  • True pos. one axis.

    Hi everybody.
    I just have a big fight with Engineer about True pos. issue. I have a question. Is it possible apply True position only one axis ? I really need this answer from the Expert.
    Thanks

  • #2
    Yes. It becomes like a ± tolerance. Often times slots will have two different one axis TP callouts.
    sigpicYou're just jealous the voices talk to me.

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    • #3
      Sorry. I am not clear for your answer, please state more details.
      Thanhks

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      • #4
        I think it is the same thing as one of our engineers dimensions his print.
        Example linear measurement he put the dims. in square/rectangle as Basic,
        and then True Pos within 2mm. The way I interpret this is that, whatever
        the deviation from the basic dim. is the True Pos.

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        • #5
          To me, it's imposible to apply True position only 1 axis. Even -B- and -C- is a straight line and print call out True pos. -C-. It still need X&Y axis. What am I wrong. Please need the ancwer.

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          • #6
            You can dimension a slot location with TP in one axis. It would look similar to the Basic dimension +/- (TP/2)
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            • #7
              Ok let make a simple alignment. Surface is -A-. Hole is -B- and Slot is -C-. But B and C are not a straight line ( X=10, Y=120 from B ). The print call out True pos. of -C-.
              My question is Why the Engineer wants me to apply only one axis to get True pos. of C ?.
              I don't do what he say unless you tell me I am wrong, because I really trust poeple in this forum I have learned since the last 4 years. The reason I say that because this Engineer know nothing about Pcdmis.
              Anyways. Thanks

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              • #8
                True Position has nothing to do with PCDMIS, it is a method of Geometric Dimensioning and Tolerancing. PCDMIS is capable of measuring and calculating True Postion. The engineer is strictly looking to control the slot location in one axis. You could dimension it as a standard tolerance. Also, do the math to show it's TP.
                When in doubt, post code. A second set of eyes might see something you missed.
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                • #9
                  Originally posted by tnguyen View Post
                  Ok let make a simple alignment. Surface is -A-. Hole is -B- and Slot is -C-. But B and C are not a straight line ( X=10, Y=120 from B ). The print call out True pos. of -C-.
                  My question is Why the Engineer wants me to apply only one axis to get True pos. of C ?.
                  I don't do what he say unless you tell me I am wrong, because I really trust poeple in this forum I have learned since the last 4 years. The reason I say that because this Engineer know nothing about Pcdmis.
                  Anyways. Thanks
                  The reason this is done - is the designer is asking for the datum feature to be 'qualified' before using it. It is a very good rule of thumb. As datum feature -C- does not exist (yet) what you MUST do is qualify the datum feature - in this case the hypotenuse in particular
                  I've been round and round with this one. The simple answer to your question is [yes] - you can ask for position on one axis. When the diameter symbol is omitted from the feature control frame, the tolerance zone is no longer "cylindrical" (or spherical), but instead could be 2 parallel planes - which the feature inspected must fall within the boundaries of.
                  Given your "nominal dimensions above", what you need to do is qualify the tertiary datum feature. This is done by actualy qualifying the hypotenuse. It is a direct straight line alignment. Your nominal dimension would be 120.4159458mm.
                  You would align your 2 feature's and aply whatever the tolerance zone is shown in the associated FCF plus or minus HALF the value given.
                  HTH
                  Kev
                  RFS Means Really Fussy Stuff

                  When all you have is a hammer - everything looks like a nail....
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                  • #10
                    Originally posted by kbotta View Post
                    When the diameter symbol is omitted from the feature control frame, the tolerance zone is no longer "cylindrical" (or spherical), but instead could be 2 parallel planes - which the feature inspected must fall within the boundaries of.


                    Exactly what I was going to out. Whenever the diameter symbol is left out of the DRF it becomes a single axis tolerance.
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                    Xcel 15-20-10 - PFXcel 7-6-5 - Merlin 11-11-7 - Romer Absolute 7525SI
                    PCDMIS 2012
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                    • #11
                      Originally posted by rangerboat72 View Post

                      Exactly what I was going to out. Whenever the diameter symbol is left out of the DRF it becomes a single axis tolerance.
                      Not the DRF (datum reference frame), the FCF (feature control frame)....is where it is found..
                      RFS Means Really Fussy Stuff

                      When all you have is a hammer - everything looks like a nail....
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                      • #12
                        The axis or direction where the tolerance should be applied is shown by the arrow that leads from the FCF to the slot. It can be evaluated as a regular dimension - one axis TP is nothing else but this, only stated a bit different. However, the deviation on the dimension times two (x 2) is the TP in this case. Not just the deviation alone.

                        Depending on the statement on the drawing, some rules do apply. The deviation of the hypothenuse is probably not what the designer intended, but the deviation in the slots width, not length and this is checked by using the alignment stated on the drawing and use one of the axis' to evaluate the dimension from the coordinatesystemaxis to the slot.

                        Hard to explain and english is not my native tongue, but I hope I am getting through. However, the drawing states how this is supposed to be evaluated and since design departments sometimes don't have the proper education when it comes to verification of the tolerances and properties they put on the drawing, this is often different from drawing to drawing.
                        PC-DMIS CAD++ 2o19 R1 SP11

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                        • #13
                          Originally posted by kbotta View Post
                          Not the DRF (datum reference frame), the FCF (feature control frame)....is where it is found..
                          Oops. I must have been getting sleepy . . .

                          Let me re-phrase that: Exactly what I was going to point out. Whenever the diameter symbol is left out of the FCF it becomes a single axis tolerance.
                          sigpic
                          Xcel 15-20-10 - PFXcel 7-6-5 - Merlin 11-11-7 - Romer Absolute 7525SI
                          PCDMIS 2012
                          Windows Office XP

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                          • #14
                            Originally posted by rangerboat72 View Post
                            Oops. I must have been getting sleepy . . .

                            Let me re-phrase that: Exactly what I was going to point out. Whenever the diameter symbol is left out of the FCF it becomes a single axis tolerance.
                            No. The diameter symbol is there to tell you "what shape" your tolerance zone is. If it is omitted, it is the distance between 2 par. planes. It could possibly be a "square" tolerance zone.
                            Also, it is not "like any other" dimension as stated above. It contains "rules" inside the FCF's datum reference. For instance - it could be a feature with an orientation constraint, and possibly a location constraint as well. It cannot be simply another +/- dimension - per the DRF.

                            Kev
                            RFS Means Really Fussy Stuff

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

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                            • #15
                              It cannot be simply another +/- dimension - per the DRF.
                              You can interpret it as a +/- tolerance. If you would take the nominal dimension of the one axis TP [minus] the measured (true) dimension you will get the deviation in one axis - take this times two and you will get the TP value. This is done after you have achieved the proper alignment, origin and coordinatesystem.

                              It is not a +/- dimension per se, but if you dissect it and know how TP is calculated you would know the similarity of those two.

                              Needless to say, the way it is put on the drawing defines how it is meant to be considered.
                              Last edited by vpt.se; 02-22-2007, 09:21 AM.
                              PC-DMIS CAD++ 2o19 R1 SP11

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