Profile vs. Flatness

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Profile vs. Flatness

    I have a part with a segmented surface that calls out profile of a surface (see attached). I take several points on each surface and construct a plane out of the points. When I dimension the profile in PC-DIMIS (FORMONLY) it spits out -.3271 (inches). Flatness, on the same constructed feature, comes out to .0169.
    What am I doing wrong here?
    Thanks,
    -Dave-
    Attached Files

  • #2
    I would assume, and without checking further into it that is all I can do, that profile, even form only has an orientation component to the calculation. Flatness does not. I would also call into question the GD&T callout. How can you have a profile of a surface without a datum referance? At that point all it is is a flatness callout anyway.
    Saving the world, one bad part at a time.

    Comment


    • #3
      Originally posted by EHines View Post
      I would assume, and without checking further into it that is all I can do, that profile, even form only has an orientation component to the calculation. Flatness does not. I would also call into question the GD&T callout. How can you have a profile of a surface without a datum referance? At that point all it is is a flatness callout anyway.
      I don't like it for a form callout either, but I don't make that decision. Regardless I do think it is a "legal" use of profile in GD&T.
      I did try dimensioning it in all six workplanes with the same result.

      Comment


      • #4
        I believe its a profile back to itself (2 surfaces)....make sure it don't rock or whatever.....been just as easy & alot less confusing to use flatness.
        sigpic.....Its called golf because all the other 4 letter words were taken

        Comment


        • #5
          Originally posted by bw_bob View Post
          I believe its a profile back to itself (2 surfaces)....make sure it don't rock or whatever.....been just as easy & alot less confusing to use flatness.
          You're right, it's form, it's to itself. It shouldn't rock they are mounting feet, investment cast stainless not machined. I've been here less than a year, I can't complain about the place but they have some "odd" (to me) practices on their drawings. I have no qualms about reporting it as flatness, but if someone questions me about why I used flatness and not profile I don't want say; because I'm ignorant of PC-DMIS and get weird numbers using profile.

          Comment


          • #6
            Legacy profile FORMONLY on a plane feature reports orientation to the active alignment. If you want to use profile tolerance instead of flatness, construct a set feature from the hits and put FORMONLY profile tolerance on the set feature.

            And BTW, there's nothing wrong with that callout. Its perfectly legal and very common. Look it up in the standard. In fact, flatness on disconnected coplanar surfaces is technically wrong.

            Comment


            • #7
              Originally posted by DJAMS View Post
              Legacy profile FORMONLY on a plane feature reports orientation to the active alignment. If you want to use profile tolerance instead of flatness, construct a set feature from the hits and put FORMONLY profile tolerance on the set feature.

              And BTW, there's nothing wrong with that callout. Its perfectly legal and very common. Look it up in the standard. In fact, flatness on disconnected coplanar surfaces is technically wrong.
              +1
              Yes, make a set from the same points you used to create the plane.
              Profile set.
              Should have worked either way, but I have a feeling there is something going on here that we cannot see.
              Can you post the code?
              Lately, it occurs to me
              What a long, strange trip it's been.

              2017 R1 (Offline programming)

              Comment


              • #8
                Yeah, sure there is more..
                the height doesn't look set to the .310 dim.. i wonder what year this drawing was released or is interpreted too? (ANSI/ASME 14.) Please post code

                Comment


                • #9
                  Originally posted by DJAMS View Post
                  Legacy profile FORMONLY on a plane feature reports orientation to the active alignment. If you want to use profile tolerance instead of flatness, construct a set feature from the hits and put FORMONLY profile tolerance on the set feature.
                  That was my mistake! I was applying profile to the constructed Plane, I made the Set and it came out fine.
                  Thanks everybody for the input.
                  -Dave-
                  Code:
                  PLN4      =FEAT/PLANE,CARTESIAN,TRIANGLE,NO
                  THEO/<0.4568,0.5221,-2.55>,<0,0,-1>
                  ACTL/<0.4567,0.522,-2.3928>,<0.0003669,-0.0004914,-0.9999998>
                  CONSTR/PLANE,BF,PNT39,PNT40,PNT41,PNT42,PNT43,PNT47,PNT48,PNT49,PNT50,,
                  OUTLIER_REMOVAL/OFF,3
                  FILTER/OFF,WAVELENGTH=0
                  
                  SCN2       =FEAT/SET,CARTESIAN
                              THEO/<0.4568,0.5221,-2.55>,<0,-1,0>
                              ACTL/<0.4567,0.522,-2.3928>,<0,-1,0>
                              CONSTR/SET,BASIC,PNT39,PNT40,PNT41,PNT42,PNT43,PNT47,PNT48,PNT49,PNT50,,
                  
                  DIM PROF2= PROFILE OF SURFACE OF SET SCN2    FORMONLY LEAST SQUARES  UNITS=IN ,$
                  GRAPH=OFF  TEXT=OFF  MULT=10.00  OUTPUT=BOTH
                  AX    NOMINAL       +TOL       -TOL       MEAS        DEV     OUTTOL
                  M      0.0000     0.0004     0.0000     0.0169     0.0169     0.0165 ------->
                  
                  DIM PROF3= PROFILE OF SURFACE OF PLANE PLN4    FORMONLY LEAST SQUARES  UNITS=IN ,$
                  GRAPH=OFF  TEXT=OFF  MULT=10.00  OUTPUT=BOTH
                  AX    NOMINAL       +TOL       -TOL       MEAS        DEV     OUTTOL
                  M      0.0000     0.0004     0.0000    -0.3271    -0.3271     0.3271 <-------
                  
                  DIM FLAT3= FLATNESS OF PLANE PLN4  UNITS=IN ,$
                  GRAPH=OFF  TEXT=OFF  MULT=10.00  OUTPUT=BOTH
                  AX    NOMINAL       +TOL       -TOL       MEAS        DEV     OUTTOL
                  M      0.0000     0.0004     0.0000     0.0169     0.0169     0.0165 ------->

                  Comment


                  • #10
                    Originally posted by dave.here View Post
                    That was my mistake! I was applying profile to the constructed Plane, I made the Set and it came out fine.
                    Thanks everybody for the input.
                    -Dave-
                    Are you sure?

                    When you are profiling in v4.3; it calculates the actual versus theoretical of each point in a feature set or plane (in your case). If you measured it with the stick then you only get the average profile of that feature set but not the actual profile because the actual and theoretical are the same, therefore it’s important for you to change the theoretical of each point before profile dimensioning. PC-DMIS does not recalculating each hit when profiling only on flatness.

                    The profile call out is questionable. If the .31 dimension is basic then it’s applied to the profile of 2 surfaces and the other question is does the .31 coming from the top left surface only or both?

                    Based on provided sketch, I would think the .31 dimension is from the top left surface only and it’s a basic dimension, I would level and origin to the top left surface, measure several points on the 2 surfaces and then create a feature set or plane. Make sure the theoretical value is .31 for each point…I know it doesn’t make sense but that how I see it with little information I have.

                    The profile can also be used on a feature itself as others have stated (.0000” location). In this case you will have to measure the 2 surfaces twice, one is establish the surfaces orientation and location and the other one for profiling, make sure the points are on the same location. You cannot use the same set of points for both, it won’t work.

                    Comment


                    • #11
                      Originally posted by EHines View Post
                      I would assume, and without checking further into it that is all I can do, that profile, even form only has an orientation component to the calculation. Flatness does not. I would also call into question the GD&T callout. How can you have a profile of a surface without a datum referance? At that point all it is is a flatness callout anyway.
                      14.5 section 6.5.4 "Applications of Datums: In most cases, profile of a surface tolerance requires reference to datums in order to provide proper orientation of the profile. With profile of a line tolerance, datums may be used under some circumstances but would not be used when the only requirement is the profile shape taken cross section by cross section - for example, the shape of a continuous extrusion."

                      Can you contact the engineer and question the lack of datum reference? It could be something as simple as he forgot to tie the profile to a datum.
                      sigpic
                      Originally posted by Ironhoe
                      I got something under my sporran for you, take care of it and you got my vote.

                      Comment


                      • #12
                        If all that is of concern is the "shape" created by the 2 surfaces....then Profile FORMONLY is fine and no datum is required.
                        The .31 dimension is not basic. It is the dimension from the profiled surface to a step up.
                        Last edited by John Riggins; 09-18-2009, 01:18 PM. Reason: spellink
                        Lately, it occurs to me
                        What a long, strange trip it's been.

                        2017 R1 (Offline programming)

                        Comment


                        • #13
                          I learned something new today. Honestly, I've never had a profile call-out that didn't relate to some datum features.
                          sigpic

                          Comment


                          • #14
                            Rob its probably on the other end of the dim line that's cut off.. lol! I think the very first ANSI14. (year 76 or 67) had dim that implied basic with no brackets , but not sure exactly. hey maybe that can be an enhancement for pc-dmis? different customer GD& T intrepretions..

                            Comment


                            • #15
                              Originally posted by cmm.re View Post
                              Rob its probably on the other end of the dim line that's cut off.. lol! I think the very first ANSI14. (year 76 or 67) had dim that implied basic with no brackets , but not sure exactly. hey maybe that can be an enhancement for pc-dmis? different customer GD& T intrepretions..
                              oh lordy.......... they will probably jump on that
                              sigpic
                              Originally posted by Ironhoe
                              I got something under my sporran for you, take care of it and you got my vote.

                              Comment

                              Related Topics

                              Collapse

                              Working...
                              X