True positions of non-circular features

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  • True positions of non-circular features

    I'm programming several parts that have a true position of a width with an MMC modifier. I have no problem measuring either side of the feature and getting the width. But the only way I know to find the true position is to ceate a midpoint and dimension the midpoint as a true position. The problem with this is that it is RFS and calculating MMC manually.

    Any help would be appreciated.

    DeWain Hodge
    Last edited by DeWain Hodge; 04-27-2007, 09:18 PM. Reason: add view of feature being measured
    DeWain Hodge

  • #2
    Create a generic feature feature such as a circle with a nominal diameter equivalent to your nominal width. Assign a variable to the measured value of the width of your slot and use it as the "measured" diameter of the created generic circle. Then do a True position with mmc on the created circle. Use the same tolerance limits for the diameter of the circle as the width of your slot.
    Last edited by rerun_lives; 04-28-2007, 12:34 PM.
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    • #3
      Maybe I'm being dense but how does this refer back to the width? What about the vectors? Would the x,y,z be the same as say the centerline of the points I'm taking for the width?

      DeWain
      DeWain Hodge

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      • #4
        Originally posted by rerun_lives View Post
        Create a generic feature feature such as a circle with a nominal diameter equivalent to your nominal width. Assign a variable to the measured value of the width of your slot and use it as the "measured" diameter of the created generic circle. Then do a True position with mmc on the created circle. Use the same tolerance limits for the diameter of the circle as the width of your slot.

        This seems interesting and appears it should work. I have some parts coming next week with slots that have true position call outs and I will have to give this a try.
        B & S XCEL 7-10-7
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        • #5
          Originally posted by rerun_lives View Post
          Create a generic feature feature such as a circle with a nominal diameter equivalent to your nominal width. Assign a variable to the measured value of the width of your slot and use it as the "measured" diameter of the created generic circle. Then do a True position with mmc on the created circle. Use the same tolerance limits for the diameter of the circle as the width of your slot.
          I do this a lot and it works great. If your feature is not square to the datums, assign variables to the IJK vectors and put them right into your generic feature.
          Xcel & MicroVal Pfx & Global 37mr4 thru 2012mr1sp3
          Contura Calypso 5.4

          Lord, keep Your arm around my shoulder and Your hand over my mouth. Amen.

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          • #6
            Originally posted by rerun_lives View Post
            Create a generic feature feature such as a circle with a nominal diameter equivalent to your nominal width. Assign a variable to the measured value of the width of your slot and use it as the "measured" diameter of the created generic circle. Then do a True position with mmc on the created circle. Use the same tolerance limits for the diameter of the circle as the width of your slot.
            What do you do about the non-width axis. Using a circle would require that axis to be perfect or it would impact the MMC calculation. Do you use the measured value of the "other" axis as the nominal?
            Links to my utilities for PCDMIS

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            • #7
              Measure the width of the slot at both ends. Use variables width or tolerance and report NONE. Create a generic circle using the vaiables of ALL of the characterstics of the mid and width points.
              Xcel & MicroVal Pfx & Global 37mr4 thru 2012mr1sp3
              Contura Calypso 5.4

              Lord, keep Your arm around my shoulder and Your hand over my mouth. Amen.

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              • #8
                example

                Pnt44 =feat/point,rect
                Theo/-1.3955,29.75,0,0.2588191,0,0.9659258
                Actl/-1.3955,29.75,0,0.2607686,-0.0000393,0.9654013
                Constr/point,mid,pnt40,pnt41
                Dim Dist3
                Ax Meas Nominal Dev +tol -tol Outtol
                M 0.75000 0.75000 0.00000 0.00000 0.00050 0.00000
                Pnt42 =feat/point,rect
                Theo/-1.3955,35.5,0.375,0,0,1
                Actl/-1.3955,35.5,0.375,0,0,1
                Constr/point,int,lin23,lin20
                Pnt43 =feat/point,rect
                Theo/-1.3955,35.5,-0.375,0,0,1
                Actl/-1.3955,35.5,-0.375,0,0,1
                Constr/point,int,lin23,lin21
                Pnt45 =feat/point,rect
                Theo/-1.3955,35.5,0,0.2588191,0,0.9659258
                Actl/-1.3955,35.5,0,0.2607686,-0.0000393,0.9654013
                Constr/point,mid,pnt42,pnt43
                Dim Dist5
                Ax Meas Nominal Dev +tol -tol Outtol
                M 0.75000 0.75000 0.00000 0.00000 0.00050 0.00000
                Assign/rtkdia = Dist3.meas
                Assign/ctrzrk = Pnt44.z
                Assign/ctrxrk = Pnt44.x
                Assign/ctryrk = Pnt44.y
                Assign/ltkdia = Dist5.meas
                Assign/ctrzlk = Pnt45.z
                Assign/ctrxlk = Pnt45.x
                Assign/ctrylk = Pnt45.y
                F2 =generic/circle,dependent,rect,out,$
                Nom/xyz,-1.3955,29.75,0,$
                Meas/xyz,ctrxrk,ctryrk,ctrzrk,$
                Nom/ijk,0,0,1,$
                Meas/ijk,0,0,1,$
                Diameter/0.75,rtkdia
                F3 =generic/circle,dependent,rect,in,$
                Nom/xyz,-1.3955,35.5,0,$
                Meas/xyz,ctrxlk,ctrylk,ctrzlk,$
                Nom/ijk,0,0,1,$
                Meas/ijk,0,0,1,$
                Diameter/0.75,ltkdia
                Dim Loc12
                Ax Meas Nominal Dev +tol -tol Bonus Outtol
                Z 0.00000 0.00000 0.00000
                Df 0.75000 0.75000 0.00000 0.00050 0.00000 0.00050 0.00000
                Tp Mmc 0.00000 0.00100 0.00050 0.00000
                End Of Dimension Loc12
                Dim Loc14
                Ax Meas Nominal Dev +tol -tol Bonus Outtol
                Z 0.00000 0.00000 0.00000
                Df 0.75000 0.75000 0.00000 0.00050 0.00000 0.00000 0.00000
                Tp Mmc 0.00000 0.00100 0.00000 0.00000
                End Of Dimension Loc14
                Robert Horne
                Va.

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                • #9
                  Originally posted by cmmguy View Post
                  What do you do about the non-width axis. Using a circle would require that axis to be perfect or it would impact the MMC calculation. Do you use the measured value of the "other" axis as the nominal?
                  You are correct CmmGuy. I'm assuming that you would use one axis only if the walls of the slot are "normal" to the relative Datum Axis'. I haven't seen the print so am making assumptions. If the slot was floating or not normal perhaps it would be best to create a generic feature out of the corner intesections if it is a square ended slot. Also, I wonder if this is a rounded end slot. I didn't think about that......
                  sigpic
                  Cold Beer MMMmmmm........

                  Dell Precision T5400
                  Windows 7
                  B&S XCEL
                  WENZEL LH1512
                  PCDMIS 2011 MR1

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                  • #10
                    A little trick I use if Iam only looking for a true pos in one direction and it keeps it real simple is to take a vector point on 1 side of the slot or feature,then 2 points on the opposite side at the same loc.Create a circle from the 3 points then dim. your true position of the circle.

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                    • #11
                      Originally posted by JIM HARRIS View Post
                      A little trick I use if Iam only looking for a true pos in one direction and it keeps it real simple is to take a vector point on 1 side of the slot or feature,then 2 points on the opposite side at the same loc.Create a circle from the 3 points then dim. your true position of the circle.
                      Wouldnt your circle be offset towards the "two point" side?
                      Links to my utilities for PCDMIS

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                      • #12
                        No,your taking the 2 points at the same loc.Try it,it works fine.

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                        • #13
                          The math for a circle wont work if two of the points are in identical locations. So that leaves me with other questions...
                          Links to my utilities for PCDMIS

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