Perp to centerline

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  • Perp to centerline

    Ok, I have a hole that I am checking that is on a 45° angle. I have done the TP as perp to centerline and I believe the numbers that I am getting based on the way that the part fits the gage. My problem is that I can't explain to my engineers why the parts are not as bad as the raw numbers look. I just don't have words small enough for them to grasp the concept.

    Here are the numbers that I get:

    Code:
    CIR1       =AUTO/CIRCLE,SHOWALLPARAMS = YES,SHOWHITS = NO
                THEO/4232.941,-599.199,1729.875,-0.0739584,0.7505775,-0.6566304,4.5
                ACTL/4232.908,-598.195,1729.692,-0.0966129,0.754098,-0.6496169,5.684
                TARG/4232.941,-599.199,1729.875,-0.0739584,0.7505775,-0.6566304
                THEO_THICKNESS = 0,RECT,IN,CIRCULAR,LEAST_SQR,ONERROR = NO,$
                AUTO MOVE = BOTH,DISTANCE = 25,RMEAS = None,None,None,$
                READ POS = NO,FIND HOLE = DISABLED,REMEASURE = NO,$
                NUMHITS = 12,INIT = 3,PERM = 3,SPACER = 3,PITCH = 0,$
                START ANG = 0,END ANG = 360,DEPTH = 2.5,$
                VOID DETECT = NO,$
                ANGLE VEC = -0.9937119,0,0.1119675
                MOVE/POINT,NORMAL,4186.808,-376.079,1717.109
                TIP/T1A7.5B180, SHANKIJK=0, 0.991, -0.131, ANGLE=-179.895
    CIR2       =AUTO/CIRCLE,SHOWALLPARAMS = YES,SHOWHITS = NO
                THEO/4268.603,-545.289,1813.897,-0.0130051,0.9973896,-0.0710277,5
                ACTL/4268.154,-544.86,1813.497,-0.0074717,0.9999516,-0.0064042,5.611
                TARG/4268.603,-545.289,1813.897,-0.0130051,0.9973896,-0.0710277
                THEO_THICKNESS = 0,RECT,IN,CIRCULAR,LEAST_SQR,ONERROR = NO,$
                AUTO MOVE = BOTH,DISTANCE = 25,RMEAS = None,None,None,$
                READ POS = NO,FIND HOLE = DISABLED,REMEASURE = NO,$
                NUMHITS = 12,INIT = 3,PERM = 3,SPACER = 3,PITCH = 0,$
                START ANG = -179.203,END ANG = -179.203,DEPTH = 2.5,$
                VOID DETECT = NO,$
                ANGLE VEC = -0.9999155,-0.0129989,0
    DIM D-S1= TRUE POSITION OF CIRCLE CIR1  UNITS=MM ,$
    GRAPH=OFF  TEXT=OFF  MULT=10.00  OUTPUT=BOTH  FIT TO DATUMS=OFF  DEV PERPEN CENTERLINE=ON  DISPLAY=DIAMETER
    AX       MEAS    NOMINAL       +TOL       -TOL      BONUS        DEV     OUTTOL
    X    4232.908   4232.941                                      -0.033           
    Y    -598.195   -599.199                                       1.004           
    Z    1729.692   1729.875                                      -0.183           
    TP                   RFS      2.000                 0.000      1.039      0.000
    END OF DIMENSION D-S1
    DIM D-S2= TRUE POSITION OF CIRCLE CIR2  UNITS=MM ,$
    GRAPH=OFF  TEXT=OFF  MULT=10.00  OUTPUT=BOTH  FIT TO DATUMS=OFF  DEV PERPEN CENTERLINE=ON  DISPLAY=DIAMETER
    AX       MEAS    NOMINAL       +TOL       -TOL      BONUS        DEV     OUTTOL
    X    4268.154   4268.603                                      -0.449           
    Y    -544.860   -545.289                                       0.429           
    Z    1813.497   1813.897                                      -0.400           
    TP                   RFS      2.000                 0.000      1.196      0.000
    END OF DIMENSION D-S2
    DIM D-S6= LOCATION OF CIRCLE CIR1  UNITS=MM ,$
    GRAPH=OFF  TEXT=OFF  MULT=10.00  OUTPUT=BOTH
    AX       MEAS    NOMINAL       +TOL       -TOL        DEV     OUTTOL
    T       0.876      0.000      1.500      1.500      0.876      0.000
    END OF DIMENSION D-S6
    DIM D-S7= LOCATION OF CIRCLE CIR2  UNITS=MM ,$
    GRAPH=OFF  TEXT=OFF  MULT=10.00  OUTPUT=BOTH
    AX       MEAS    NOMINAL       +TOL       -TOL        DEV     OUTTOL
    T       0.462      0.000      1.500      1.500      0.462      0.000
    END OF DIMENSION D-S7
    The problem is the y-axis for cir1. If anyone knows how PC-DMIS calculates and can help me out I would apreciate it.
    Saving the world, one bad part at a time.

  • #2
    On 2 D features, why are your IJK vectors off like that? They should be true to one of the axes.
    Links to my utilities for PCDMIS

    Comment


    • #3
      I think I attached a 3d layout of your actual CIR1 versus measured.
      my calculated TP is 1.04862 (2 x .52431) - is pretty close.
      I believe the layout illutrates the concept.

      Aparently attachment did not make it - will pm it if I can
      Last edited by RussL; 09-25-2007, 12:05 PM.

      Comment


      • #4
        Try telling them that the SURFACE deviation is removed from the TP value when calculating PERP to CENTER LINE.
        sigpic
        Originally posted by AndersI
        I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

        Comment


        • #5
          The circles are measured as 3d features with nominals from CAD.
          Saving the world, one bad part at a time.

          Comment


          • #6
            Originally posted by EHines View Post
            The circles are measured as 3d features with nominals from CAD.
            Ok, someone tell me why you would measure 2d features(circles) as 3d features? I dont get that.
            Links to my utilities for PCDMIS

            Comment


            • #7
              Originally posted by cmmguy View Post
              Ok, someone tell me why you would measure 2d features(circles) as 3d features? I dont get that.
              UNLESS the circle has vectors that are exactly square (0,0,1, 0,1,0, 1,0,0), then it IS a 3-D feature. It may have a 2-D cross section, but it IS 3-D. ALL automotive circles (re holes) are 3-D features. The circle can move in it's cross-section plane as well as in the direction of the surface variation and this CAN have an effect of the location, depending on the application.
              sigpic
              Originally posted by AndersI
              I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

              Comment


              • #8
                Originally posted by kass_b
                your vectors for circle one and two are differnt in y should be the same?

                No, these are two different holes on different planes measured independantly back to the datums with a position tolerance of 2.0mm. Both holes measure good back to the datums and both are within the profile tolerance for the surfaces they are in. My problem is trying to explain why the Y-axis on cir1 doesn't have to be moved according to the tolerances on the print.
                Saving the world, one bad part at a time.

                Comment


                • #9
                  Originally posted by cmmguy View Post
                  Ok, someone tell me why you would measure 2d features(circles) as 3d features? I dont get that.
                  Only time I have done this is when the pierce point Diameter is called out Spatial TP. We have that on some of our parts.
                  Bill Jarrells
                  A lie can travel half way around the world while the truth is putting on its shoes. - Mark Twain

                  Comment


                  • #10
                    Originally posted by EHines View Post
                    No, these are two different holes on different planes measured independantly back to the datums with a position tolerance of 2.0mm. Both holes measure good back to the datums and both are within the profile tolerance for the surfaces they are in. My problem is trying to explain why the Y-axis on cir1 doesn't have to be moved according to the tolerances on the print.
                    Try this:

                    1) Use 3 surface sample hits (you SHOULD be using 1 minimum anyway)
                    2) Report the "S" for the feature.

                    Not sure which versions this works correctly in, but the "S" axis SHOULD report the SURFACE deviaiton only (along the vector) for these Autofeatures: Circle, Round Slot, Square Slot, Edge point. (may be others, but it SHOULD work for these).
                    sigpic
                    Originally posted by AndersI
                    I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

                    Comment


                    • #11
                      Originally posted by Matthew D. Hoedeman View Post
                      UNLESS the circle has vectors that are exactly square (0,0,1, 0,1,0, 1,0,0), then it IS a 3-D feature. It may have a 2-D cross section, but it IS 3-D. ALL automotive circles (re holes) are 3-D features. The circle can move in it's cross-section plane as well as in the direction of the surface variation and this CAN have an effect of the location, depending on the application.
                      This must be unique to sheet metal. A circle is 2D in that you have to define its axes before measurement. You cannot measure a circle and extract its axis from the data(unless it is projected onto a surface.
                      Links to my utilities for PCDMIS

                      Comment


                      • #12
                        Originally posted by Matthew D. Hoedeman View Post
                        Try this:

                        1) Use 3 surface sample hits (you SHOULD be using 1 minimum anyway)
                        2) Report the "S" for the feature.

                        Not sure which versions this works correctly in, but the "S" axis SHOULD report the SURFACE deviaiton only (along the vector) for these Autofeatures: Circle, Round Slot, Square Slot, Edge point. (may be others, but it SHOULD work for these).
                        I measured the hole with three surface hits and included the T for each feature (aparently in a case like this T and S are the same). Even using the difference between the T and Y deviation I can not make the TP calcualtion by hand.
                        Saving the world, one bad part at a time.

                        Comment


                        • #13
                          If you want 3D True Position simply project the Circle to the Plane.
                          Or, Temp Align to PLane before Auto Circle. Then when you recall the original Datum your feature is 3D. If I am misunderstanduing this then disregard.
                          Bill Jarrells
                          A lie can travel half way around the world while the truth is putting on its shoes. - Mark Twain

                          Comment


                          • #14
                            Originally posted by EHines View Post
                            I measured the hole with three surface hits and included the T for each feature (aparently in a case like this T and S are the same). Even using the difference between the T and Y deviation I can not make the TP calcualtion by hand.
                            I took the hole data (measured AND nominal) and put those 2 points into my cad system. I construct the vector line of the hole then did the calcualtions.

                            TP radially = 0.520, TP diameter = 1.04, perp to center line
                            Surface deviation 0.876

                            So, the "T" is reporting the surface deviation and your TP is reporting correctly.

                            So, we ALL now know that the numbers on the report are correct. So, now you have to figure out some way to show the, er, 'intelligent' people why the numbers look like they do.

                            Tell them to do exactly what I did:
                            1) Create a point in a cad package at the NOMINAL location
                            2) Create a point at the ACTUAL location
                            3) Create a point to represent the VECTOR of the hole (I just offset the nominal in each axis by 10 times the vector, just to get it 'away' from the other points)
                            4) Create a 3-D line from the NOMINAL to teh VECTOR point
                            5) Ask it the distance of the ACTUAL point to the 3-D line, then DOUBLE the amount for the TP deviation
                            6) Construct a plane perpendicular to the LINE going through the NOMINAL point
                            7) Ask it the distance of the ACTUAL point to the PERP PLANE. ALl the values will match your report.

                            If they can't "get it" at that point, then tell them to turn in their pocket protectors and go home.
                            sigpic
                            Originally posted by AndersI
                            I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

                            Comment


                            • #15
                              Originally posted by Wingman View Post
                              If you want 3D True Position simply project the Circle to the Plane.
                              Or, Temp Align to PLane before Auto Circle. Then when you recall the original Datum your feature is 3D. If I am misunderstanduing this then disregard.

                              According to the gage and my understanding of how the parts fit into the vehicle I believe that the numbers I am reporting are correct. I just want to be able to explain WHY the numbers are correct to my 11 year old daughter (or someone with about as much technical understanding).

                              Try telling them that the SURFACE deviation is removed from the TP value when calculating PERP to CENTER LINE.
                              I think that Matt is saying what I want here, but I just keep getting blank stares and confused looks. I am trying to figure out the calculations behind perp to center and maybe the numbers will finially make sense...but probably not.
                              Saving the world, one bad part at a time.

                              Comment

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