Problem With Coaxial Holes

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  • Problem With Coaxial Holes

    How does pc-dmis calculate coaxiality? I got a problem with this holes as you see cyl2 to cly3 the position of the two cylinder only has a difference of .0003 since cyl2 Y= -.0001 and cyl3 Y= +.0002. The X is the same .0001. How does it makes this .0015 coax ? Same issue with the other two hole with cyl4 to cyl5. See screen shoot of the measured holes. The circles are measured so I can see if the holes are tapering and also used them to create the cylinders.

    Edit.:Attachment looks too small to read. Not sure why .
    Last edited by BANDY; 05-01-2008, 07:59 PM.
    Pc-Dmis 4.2, Zeiss Eclipse
    sigpic

  • #2
    I'm going to guess that the difference is due to alignment. When you dimension the position, I am guessing you are aligned to something other than these holes. These dimensions would be to the centroid of the cylinder unless you have projected them to a particular plane.

    When you do coaxiality, alignment is ignored. I would guess that the coaxiality dimension you see is the maximum distance from any point on the axis of your first feature to the axis of your datum feature (second feature) perpendicular to your datum feature.

    Just a guess.

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    • #3
      The alignment is done by plane 1 which is leveled then I have created two cylinders out of the four holes then use them to rotate and align the part. One of the cylinder is actually set to my origin. Per B/P plane 1 is datum -A- hole 1 is datum -B- and hole two is datum -C-.

      edit: let see if this attachment is big enough.
      Last edited by BANDY; 05-01-2008, 07:59 PM.
      Pc-Dmis 4.2, Zeiss Eclipse
      sigpic

      Comment


      • #4
        Originally posted by BANDY View Post
        The alignment is done by plane 1 which is leveled then I have created two cylinders out of the four holes then use them to rotate and align the part. One of the cylinder is actually set to my origin. Per B/P plane 1 is datum -A- hole 1 is datum -B- and hole two is datum -C-.
        Goodluck nailed it. When doing coaxiality the 2nd Feature becomes the Datum Feature. Datum A is no longer considered. The first cylinder is reported in the relation to the Axis of the 2nd feature. It is basically the same as if you leveled to the 2nd Cylinder and set your Origin to it then reported true position of the 2nd Cylinder.
        Bill Jarrells
        A lie can travel half way around the world while the truth is putting on its shoes. - Mark Twain

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        • #5
          I check the TP , for both cyl, it shows .0003 at both case. Isn't coaxiality check the center of cly3 then cyl2 and report the different between? I am getting this all wrong?


          DIM LOC13= TRUE POSITION OF CYLINDER CYL3 USE AXIS=AVERAGE REF LENGTH=0.0000 UNITS=IN ,$
          GRAPH=OFF TEXT=OFF MULT=10.00 OUTPUT=BOTH FIT TO DATUMS=ON DEV PERPEN CENTERLINE=OFF DISPLAY=DIAMETER
          AX NOMINAL MEAS +TOL -TOL BONUS DEV OUTTOL
          X 0.0000 0.0001 0.0001
          Y 0.0000 0.0002 0.0002
          DF 0.7528 0.7531 0.0005 0.0005 0.0002 0.0003 0.0000 -------#-
          D1 PLANE PLN1 AT RFS
          D2 0.7528 0.7533 0.0005 0.0005 CYLINDER CYL6 AT RFS
          D3 0.7528 0.7533 0.0005 0.0005 CYLINDER CYL7 AT RFS
          TP MMC 0.0010 0.0002 0.0003 0.0000 --#------
          END OF DIMENSION LOC13
          DIMINFO/LOC13;ICON,DIMID,FEATID,VERT,HORIZ, ,$
          HEADINGS,GRAPH AXIS;MEAS, , , , , , , , ,$
          X,Y,DF,D1,D2,D3,TP, , , , , , , , ,
          DIM LOC14= TRUE POSITION OF CYLINDER CYL2 USE AXIS=AVERAGE REF LENGTH=0.0000 UNITS=IN ,$
          GRAPH=OFF TEXT=OFF MULT=10.00 OUTPUT=BOTH FIT TO DATUMS=ON DEV PERPEN CENTERLINE=OFF DISPLAY=DIAMETER
          AX NOMINAL MEAS +TOL -TOL BONUS DEV OUTTOL
          X 0.0000 0.0001 0.0001
          Y 0.0000 -0.0001 -0.0002
          DF 0.7528 0.7535 0.0005 0.0005 0.0000 0.0007 0.0002 -------->
          D1 PLANE PLN1 AT RFS
          D2 0.7528 0.7533 0.0005 0.0005 CYLINDER CYL6 AT RFS
          D3 0.7528 0.7533 0.0005 0.0005 CYLINDER CYL7 AT RFS
          TP MMC 0.0010 0.0000 0.0003 0.0000 --#------
          END OF DIMENSION LOC14
          DIMINFO/LOC14;ICON,DIMID,FEATID,VERT,HORIZ, ,$
          HEADINGS,GRAPH AXIS;MEAS, , , , , , , , ,$
          X,Y,DF,D1,D2,D3,TP, , , , , , , , ,
          Pc-Dmis 4.2, Zeiss Eclipse
          sigpic

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          • #6
            Originally posted by BANDY View Post
            I check the TP , for both cyl, it shows .0003 at both case. Isn't coaxiality check the center of cly3 then cyl2 and report the different between? I am getting this all wrong?


            DIM LOC13= TRUE POSITION OF CYLINDER CYL3 USE AXIS=AVERAGE REF LENGTH=0.0000 UNITS=IN ,$
            GRAPH=OFF TEXT=OFF MULT=10.00 OUTPUT=BOTH FIT TO DATUMS=ON DEV PERPEN CENTERLINE=OFF DISPLAY=DIAMETER
            AX NOMINAL MEAS +TOL -TOL BONUS DEV OUTTOL
            X 0.0000 0.0001 0.0001
            Y 0.0000 0.0002 0.0002
            DF 0.7528 0.7531 0.0005 0.0005 0.0002 0.0003 0.0000 -------#-
            D1 PLANE PLN1 AT RFS
            D2 0.7528 0.7533 0.0005 0.0005 CYLINDER CYL6 AT RFS
            D3 0.7528 0.7533 0.0005 0.0005 CYLINDER CYL7 AT RFS
            TP MMC 0.0010 0.0002 0.0003 0.0000 --#------
            END OF DIMENSION LOC13
            DIMINFO/LOC13;ICON,DIMID,FEATID,VERT,HORIZ, ,$
            HEADINGS,GRAPH AXIS;MEAS, , , , , , , , ,$
            X,Y,DF,D1,D2,D3,TP, , , , , , , , ,
            DIM LOC14= TRUE POSITION OF CYLINDER CYL2 USE AXIS=AVERAGE REF LENGTH=0.0000 UNITS=IN ,$
            GRAPH=OFF TEXT=OFF MULT=10.00 OUTPUT=BOTH FIT TO DATUMS=ON DEV PERPEN CENTERLINE=OFF DISPLAY=DIAMETER
            AX NOMINAL MEAS +TOL -TOL BONUS DEV OUTTOL
            X 0.0000 0.0001 0.0001
            Y 0.0000 -0.0001 -0.0002
            DF 0.7528 0.7535 0.0005 0.0005 0.0000 0.0007 0.0002 -------->
            D1 PLANE PLN1 AT RFS
            D2 0.7528 0.7533 0.0005 0.0005 CYLINDER CYL6 AT RFS
            D3 0.7528 0.7533 0.0005 0.0005 CYLINDER CYL7 AT RFS
            TP MMC 0.0010 0.0000 0.0003 0.0000 --#------
            END OF DIMENSION LOC14
            DIMINFO/LOC14;ICON,DIMID,FEATID,VERT,HORIZ, ,$
            HEADINGS,GRAPH AXIS;MEAS, , , , , , , , ,$
            X,Y,DF,D1,D2,D3,TP, , , , , , , , ,
            Coaxiality ignores Datum A. TP as you have done here reports to Datum A. Coaxiality reports Cylinder 1 TP to the AXIS of Cylinder 2.
            Try Leveling to Cylider 2. Translate to cylinder 2. THEN report TP and you will see what I mean - it should report the same as Coaxiality.
            Bill Jarrells
            A lie can travel half way around the world while the truth is putting on its shoes. - Mark Twain

            Comment


            • #7
              Look at it this way.
              In the first cae (TP) you have a perpendicular line shooting straight out of the PLane and you are comparing the center of teh two cylinders to that line.
              In the second case you have a line through the Axis of one Cylinder (the 2nd Cylinder of your command) and you are comparing the other cylinder to this axis. The two lines are not parallel.
              Bill Jarrells
              A lie can travel half way around the world while the truth is putting on its shoes. - Mark Twain

              Comment


              • #8
                Thanks for not giving up on me I be back to this holes but I need to move on.
                Pc-Dmis 4.2, Zeiss Eclipse
                sigpic

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                • #9
                  This is what I was trying to explain.
                  Attached Files

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                  • #10
                    Originally posted by Goodluck View Post
                    This is what I was trying to explain.
                    PERFECT!
                    Bill Jarrells
                    A lie can travel half way around the world while the truth is putting on its shoes. - Mark Twain

                    Comment


                    • #11
                      Thank You for the sketch ! I understand now.
                      Pc-Dmis 4.2, Zeiss Eclipse
                      sigpic

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                      • #12
                        my print

                        I usually don't need to deal with this close tolerance holes and coaxial holes, I interpret this print wants me those two holes to be w/in .001 coaxial. Am I getting this right? Datum A is perpendicular to the holes, datum B is the other set of holes. Is it necessary to ender distance between the cly.?
                        Last edited by BANDY; 05-01-2008, 07:59 PM.
                        Pc-Dmis 4.2, Zeiss Eclipse
                        sigpic

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