Symmetry Issue

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  • Symmetry Issue

    I am having trouble with a getting symmetry of a slot.
    I have Small part which is of Ø0.6975 inches it consists of 4 Slots and 2 holes and inner dia is my datum, now the drawing calls out symmetry | 0.002 | A . i know that symmetry can be measured only with Planes & Lines. so i created generic feature (Plane) for datum and reported results.
    My Result is not constant.
    i'm using 2013 & TP20 probe with Ø2 x 30mm Stylus....
    Am I doing this right or wrong ?. Any help would be appreciated.




    Capture1.PNGCapture2.PNG

    Top View ________________________ Front view


    Code:
    SLT_1_ALN  =FEAT/CONTACT/CYLINDER/DEFAULT,CARTESIAN,IN,LEAST_SQR
                THEO/<0+0,0-0.3487,0-0.0457>,<0*0,-1*1,0*0>,0.1585,0.1788
                ACTL/<-0.0011,-0.3487,-0.0454>,<-0.0018975,-0.9999982,-0.0000803>,0.16,0.1788
                TARG/<0+0,0-0.3487,0-0.0457>,<0*0,-1*1,0*0>
                START ANG=280,END ANG=80
                ANGLE VEC=<0,0,-1>
                DIRECTION=CCW
                SHOW FEATURE PARAMETERS=NO
                SHOW CONTACT PARAMETERS=NO
    A7         =ALIGNMENT/START,RECALL:A6,LIST=YES
                ALIGNMENT/LEVEL,ZPLUS,Z_PLN
                ALIGNMENT/ROTATE,YMINUS,TO,SLT_ALN_1,ABOUT,ZPLUS
                ALIGNMENT/TRANS,XAXIS,DATUM_A
                ALIGNMENT/TRANS,YAXIS,DATUM_A
                ALIGNMENT/TRANS,ZAXIS,SLT_ALN_1
                ALIGNMENT/END
                MOVE/POINT,NORMAL,<0+0,0-0.24,0+0.1>
                DISPLAYPRECISION/5
    SLT_A_P1   =FEAT/CONTACT/VECTOR POINT/DEFAULT,CARTESIAN
                THEO/<0-0.07925,0-0.29,0+0.02>,<1*1,0*0,0*0>
                ACTL/<-0.07979,-0.28988,0.01982>,<1,0,0>
                TARG/<0-0.07925,0-0.290,0+0.02>,<1*1,0*0,0*0>
                SNAP=NO
                SHOW FEATURE PARAMETERS=NO
                SHOW CONTACT PARAMETERS=NO
    SLT_A_P2   =FEAT/CONTACT/VECTOR POINT/DEFAULT,CARTESIAN
                THEO/<0-0.07925,0-0.255,0+0.02>,<1*1,0*0,0*0>
                ACTL/<-0.07984,-0.25446,0.01991>,<1,0,0>
                TARG/<0-0.07925,0-0.255,0+0.02>,<1*1,0*0,0*0>
                SNAP=NO
                SHOW FEATURE PARAMETERS=NO
                SHOW CONTACT PARAMETERS=NO
    SLT_A_P3   =FEAT/CONTACT/VECTOR POINT/DEFAULT,CARTESIAN
                THEO/<0-0.07925,0-0.22,0+0.02>,<1*1,0*0,0*0>
                ACTL/<-0.07991,-0.21934,0.01988>,<1,0,0>
                TARG/<0-0.07925,0-0.22,0+0.02>,<1*1,0*0,0*0>
                SNAP=NO
                SHOW FEATURE PARAMETERS=NO
                SHOW CONTACT PARAMETERS=NO
    SLT_A_L1   =FEAT/LINE,CARTESIAN,UNBOUNDED,YES
                THEO/<0-0.07925,0-0.29,0+0.02>,<0*0,1*1,0*0>
                ACTL/<-0.07979,-0.28988,0.01984>,<-0.0016712,0.9999983,0.0007936>
                CONSTR/LINE,BF,3D,SLT_A_P1,SLT_A_P2,SLT_A_P3,,
                OUTLIER_REMOVAL/OFF,3
                FILTER/OFF,WAVELENGTH=0
    SLT_A_P4   =FEAT/CONTACT/VECTOR POINT/DEFAULT,CARTESIAN
                THEO/<0+0.07925,0-0.22,0+0.02>,<-1*1,0*0,0*0>
                ACTL/<0.07911,-0.21998,0.02002>,<-1,0,0>
                TARG/<0+0.07925,0-0.22,0+0.02>,<-1*1,-0.0000421,0>
                SNAP=NO
                SHOW FEATURE PARAMETERS=NO
                SHOW CONTACT PARAMETERS=NO
    SLT_A_P5   =FEAT/CONTACT/VECTOR POINT/DEFAULT,CARTESIAN
                THEO/<0+0.07925,0-0.255,0+0.02>,<-1*1,0*0,0*0>
                ACTL/<0.07913,-0.25556,0.02>,<-1,0,0>
                TARG/<0+0.07925,0-0.255,0+0.02>,<-1*1,-0.0000421,0>
                SNAP=NO
                SHOW FEATURE PARAMETERS=NO
                SHOW CONTACT PARAMETERS=NO
    SLT_A_P6   =FEAT/CONTACT/VECTOR POINT/DEFAULT,CARTESIAN
                THEO/<0+0.07925,0-0.29,0+0.02>,<-1*1,0*0,0*0>
                ACTL/<0.07908,-0.29059,0.02005>,<-1,0,0>
                TARG/<0+0.07925,0-0.29,0+0.02>,<-1*1,0*0,0*00>
                SNAP=NO
                SHOW FEATURE PARAMETERS=NO
                SHOW CONTACT PARAMETERS=NO
    SLT_A_L2   =FEAT/LINE,CARTESIAN,UNBOUNDED,YES
                THEO/<0+0.07925,0-0.29,0+0.02>,<0.0000421,-1,0>
                ACTL/<0.07912,-0.21998,0.02001>,<-0.0004891,-0.9999998,0.0004177>
                CONSTR/LINE,BF,3D,SLT_A_P4,SLT_A_P5,SLT_A_P6,,
                OUTLIER_REMOVAL/OFF,3
                FILTER/OFF,WAVELENGTH=0
    SLT_A_MIDLIN=FEAT/LINE,CARTESIAN,UNBOUNDED,YES
                THEO/<0+0,0-0.29,0+0.02>,<0*0,1*1,0*0>
                ACTL/<-0.00037,-0.25495,0.01992>,<-0.000591,0.9999998,0.0001879>
                CONSTR/LINE,MID,SLT_A_L1,SLT_A_L2
    A16        =ALIGNMENT/START,RECALL:A11,LIST=YES
                ALIGNMENT/LEVEL,ZPLUS,DATUM_A
                ALIGNMENT/ROTATE,YPLUS,TO,SLT_A_MIDLIN,ABOUT,ZPLUS
                ALIGNMENT/TRANS,XAXIS,DATUM_A
                ALIGNMENT/TRANS,YAXIS,DATUM_A
                ALIGNMENT/TRANS,ZAXIS,Z_PLN
                ALIGNMENT/END
    DATUM_A1   =GENERIC/PLANE,DEPENDENT,CARTESIAN,$
                NOM/XYZ,<DATUM_A.TX,DATUM_A.TY,DATUM_A.TZ>,$
                MEAS/XYZ,<DATUM_A.X,DATUM_A.Y,DATUM_A.Z>,$
                NOM/IJK,<1*1,0*0,0*0>,$
                MEAS/IJK,<1*1,0*0,0*0>
                DATDEF/FEATURE=DATUM_A1,A1
    DIM_2_1 =SYMMETRY : SLT_A_L1,SLT_A_L2
                FEATCTRLFRAME/SHOWPARAMS=NO,SHOWEXPANDED=NO
                  DIMENSION/SYMMETRY,0.002,A1,
                  NOTE/DIM_2_1
                FEATURES/SLT_A_L1,SLT_A_L2,,

  • #2
    Does your callout reference 2X or 4X for the slots? If it were treated as 2X so the lines were longer, I bet it would repeat better. Also, your vector for SLT_A_L2 is also incorrect. Do(es) your previous alignment(s) lock down all 6 DOF? You shouldn't need to use *1 or +0 to control theos

    Comment


    • #3
      Drawing callouts 4x and thanks for addressing the error...
      I want to check 10 parts in single run... To do that I use do loop, because of that nly I'm using *1 & +0 to control Theo's....

      Comment


      • #4
        Have you tried creating the midplane by creating midpoints instead of 2 planes??

        Comment


        • #5
          No, so far I just took 3 points on each side of slot face ,constructed 3D line & reported in xactmeasure by selecting both lines.
          For Datum I constructed generic plane..

          Comment


          • #6
            You should be able to create the lines as well.

            Comment


            • #7
              Symmetry is by far the worst GD&T callout, in regards to the frequency of times I've seen engineers incorrectly apply it to a drawing. --I'm so happy it's been removed from 2018 rev.

              You have symmetry of the 4 slots as defined by "4x" then [Symmetry][0.002][A]
              Symmetry is supposed to only apply to planar features of size, and needs to be judged 'congruent with the datum axis or centerplane of the datum features referenced" (from GD&T ASME Y14.5m 1994 SAE training). Basically, this means your tolerance zone is only controlling parallelism of each slot's mid plane along the A datum axis line.

              The symmetry callout can be argued to apply a parallel plane radiating as a ray line outward from the A datum axis, controlling location. You should also apply simultaneity for all four midplanes and applied with 90° equidistant planar zones radiating away from A axis can be (implied by orthogonal rule).

              But this is totally ambiguous and a bullsh!t callout if that's what they expect. 0.002" variation on the location of all 4 midplanes, at the same time, relative to A is going to be a tough one to meet.
              I'd ask for clarification of the dimension by engineering or the customer, before I went ahead and started compiling all of that.


              Comment


              • #8
                Here is my drawing .....

                IMG-20190703-WA0001__01.jpg

                Comment


                • #9
                  I'd make a really accurate A cylinder. Level/origin to it.
                  I'd make a plane on the top of the part.
                  Then, I'd make 2 planes and a midplane for each of the 90 degree slots (full width through A).
                  Intersect the midplanes to the top plane to create two lines.

                  I'd create a bestfit rotation alignment, using the two mid-lines, still level to A.
                  Then, finally, I'd report symmetry of each midplane to A.
                  Last edited by louisd; 07-02-2019, 04:09 PM.

                  Comment


                  • #10
                    Thank you for your response.... Tomorrow will give a try....

                    Comment


                    • #11
                      Does the probe factor affect repetability ? , now i'm getting repetability in 0.0005"
                      i'm using TP20 Ø 3 x30 with 3mm/sec touch speed

                      Comment


                      • louisd
                        louisd commented
                        Editing a comment
                        all probing parameters can affect repeatability. If you used a smaller diameter probe, you'd most likely be able to measure more surface area of the planes, and have a more prudent prehit/retract distance while probing within the slot. I'd have selected s 2mm sphere for part features this small.

                    • #12
                      Originally posted by Thiyagu_Raj View Post
                      Does the probe factor affect repetability ? , now i'm getting repetability in 0.0005"
                      i'm using TP20 Ø 3 x30 with 3mm/sec touch speed
                      AFAIK, the slower the touch speed, the more accurate. BUT and that's a big but... The touch speed MUST be the same as the touch speed used when calibrating the probe.

                      Comment


                      • #13

                        https://www.pcdmisforum.com/core/image.php?userid=23134&thumb=1&dateline=1498857830
                        #11.1
                        louisd commented

                        all probing parameters can affect repeatability. If you used a smaller diameter probe, you'd most likely be able to measure more surface area of the planes, and have a more prudent prehit/retract distance while probing within the slot. I'd have selected s 2mm sphere for part features this small.


                        the part is having another 2 holes horizontally 45° to the slot so, i need to rotate the head. if the part orientation is not perfect shank will hit, because of that i planned for Ø3 ball.....

                        Comment

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