Coaxial Features Without Datum References

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

  • Coaxial Features Without Datum References

    Rob Jensen

    Don Ruggieri

    neil.challinor

    I have a part that has two bores of different diameters that creates datum feature A with the notation of TWO COAXIAL FEATURES called out in the model. They have a diametrical position callout without datum references. This is a legitimate callout per ASME Y14.5 7.6.2.3. PCDMIS will not allow me to pick both cylinders nor will it allow me to dimension the position without datum references in either Exactmeasure or Geotolerance. What should I use in the software to properly dimension this callout? 2020R2 will not allow a 3D line as a primary datum. What is the proper way (inscribed cylinder, least squared, line, etc.) to define these coaxial bores as primary datum feature A?
    153010 Global Advantage w/ LSPX1H_T Analog Probe
    7107 Global Classic TP20
    2019R1 SP1 CAD++

  • #2
    Can't you define one bore as a datum feature and request the position from one to the other?

    Comment


    • RIDER
      RIDER commented
      Editing a comment
      Yes and that's probably what I will end up having to do; however, that's not how it is modeled. The model has two leader lines pointing to both bores with datum feature A attached and the feature control frame of diametrical position of 0.002" with the note TWO COAXIAL HOLES underneath.

  • #3
    Legacy dimensioning probably needed.

    B&S CHAMELEON/PCDMIS CAD++ V2011

    There are no bugs, only "UNDOCUMENTED ENHANCEMENTS!"

    sigpic

    Comment


    • #4
      Can you post a copy of the print? If not at least a sketch on a cocktail napkin? I am having a hard time envisioning your situation. A lot of my parts are lathe jobs that have A-B type datum structures and coaxiality/concentricity stuff.
      Last edited by DAN_M; 11-18-2020, 12:18 PM.
      SF7107(PCD), SF454(PCD), 152614(Quindos), 9159(Quindos), 7107(Quindos), B&S Manual, M&M Gear Checker

      Comment


      • #5
        Depending how long those features are and how far apart they are can / may pose issues. I know I have done multiple circles on features and done constructed line based on the circles and used straightness of a line for some reference ? This isnt getting you all the way there but a start. Maybe reference each cylinder back to the line ?

        Comment


        • #6
          Here's a snippit

          one bore is 0.5±0.0003" and the other bore is 0.5625 +0.0015 / -0.0000
          Attached Files
          Last edited by RIDER; 11-18-2020, 12:31 PM.
          153010 Global Advantage w/ LSPX1H_T Analog Probe
          7107 Global Classic TP20
          2019R1 SP1 CAD++

          Comment


          • #7
            RIDER



            It is legit to have GDT called out on a print without datum references.

            Still, a T.P. needs basic dimensions. It needs to be toleranced back to something.

            If I understand you correctly, your model governs the position of the stuff you're measuring. Which is fine. That being said...since you have no datums..you'd need to speak to your engineers and have them specify which features of the part they'd like you to use for the datum structure to check the GD&T back to. Leveling off the top and then making the ID the origin could be drastically mathematically different then leveling through a cylinder then making a corner the origin. You don't want to approach something that is wide open to interpretation then send your machinists on a wild goose chase trying to fix the part if its actually good. As a programmer its not really our job to design the part, its our job to execute the instructions on the print and then raise the flag if we don't have enough info to proceed (I'd argue that's where you are right now).

            Above being said, I'd hammer down your base origin with your engineering team.

            Then, make an axis as shown below.

            Then, report the true position of that axis back to your alignment. I used Y- workplane so I reported the XZ position of the axis.


            Code:
            STARTUP =ALIGNMENT/START,RECALL:USE_PART_SETUP,LIST=YES
            ALIGNMENT/END
            MODE/MANUAL
            FORMAT/TEXT,OPTIONS, ,HEADINGS,SYMBOLS, ;NOM,TOL,MEAS,DEV,OUTTOL, ,
            LOADPROBE/7107_Y_3X40
            TIP/T1A-90B0, SHANKIJK=0, -1, 0, ANGLE=0
            WORKPLANE/YMINUS
            CIR_5 =FEAT/CONTACT/CIRCLE/DEFAULT,CARTESIAN,IN,LEAST_SQR
            THEO/<6,1,2>,<0,-1,0>,0.5
            ACTL/<6,1,2>,<0,-1,0>,0.5
            TARG/<6,1,2>,<0,-1,0>
            START ANG=0,END ANG=360
            ANGLE VEC=<0,0,1>
            DIRECTION=CCW
            SHOW FEATURE PARAMETERS=NO
            SHOW CONTACT PARAMETERS=NO
            CIR_7 =FEAT/CONTACT/CIRCLE/DEFAULT,CARTESIAN,IN,LEAST_SQR
            THEO/<6,2,2>,<0,-1,0>,0.5625
            ACTL/<6,2,2>,<0,-1,0>,0.5625
            TARG/<6,2,2>,<0,-1,0>
            START ANG=0,END ANG=360
            ANGLE VEC=<0,0,1>
            DIRECTION=CCW
            SHOW FEATURE PARAMETERS=NO
            SHOW CONTACT PARAMETERS=NO
            PNT1 =FEAT/POINT,CARTESIAN,NO
            THEO/<6,1,2>,<0,-1,0>
            ACTL/<6,1,2>,<0,-1,0>
            CONSTR/POINT,CAST,CIR_5
            PNT2 =FEAT/POINT,CARTESIAN,NO
            THEO/<6,2,2>,<0,-1,0>
            ACTL/<6,2,2>,<0,-1,0>
            CONSTR/POINT,CAST,CIR_7
            WORKPLANE/ZPLUS
            LIN_AXIS_A =FEAT/LINE,CARTESIAN,UNBOUNDED,NO
            THEO/<6,1,2>,<0,1,0>
            ACTL/<6,1,2>,<0,1,0>
            CONSTR/LINE,BF,3D,PNT1,PNT2,,
            OUTLIER_REMOVAL/OFF,3
            FILTER/OFF,WAVELENGTH=0
            WORKPLANE/YMINUS
            DIM DIM_1= POSITION OF LINE LIN_AXIS_A UNITS=IN ,$
            GRAPH=OFF TEXT=OFF MULT=10.00 OUTPUT=BOTH FIT TO DATUMS=OFF DEV PERPEN CENTERLINE=OFF DISPLAY=DIAMETER
            AX NOMINAL +TOL -TOL BONUS MEAS DEV OUTTOL
            X 6.0000 6.0000 0.0000
            Z 2.0000 2.0000 0.0000
            TP RFS 0.0050 0.0000 0.0000 0.0000 0.0000 #--------
            END OF DIMENSION DIM_1
            Last edited by DAN_M; 11-18-2020, 01:24 PM.
            SF7107(PCD), SF454(PCD), 152614(Quindos), 9159(Quindos), 7107(Quindos), B&S Manual, M&M Gear Checker

            Comment


            • ctw00
              ctw00 commented
              Editing a comment
              Datums aren't required for coaxial features as his was drawn, they just have to measure good to each other. (In ASME Y14.5-2009 it is covered under '7.6.2.3 Coaxial Features Without Datum References.')

          • #8
            DAN_M
            A is the two coaxial holes
            B is a face that the smaller hole goes through
            C is a back face that is "almost" perpendicular to B

            I have the holes running in the Z axis so I can measure them with a A0B0 probe angle. I measured 4 circles equally spaced on each bore. Then I constructed a 3D line through all 8 circles. I constructed a line from the intersection of planes B & C. I leveled the Z+ to the 3D line, rotated X+ to the intersection line, XY origin on the 3D line and Z origin on the B plane.
            I constructed two cylinders out of the 8 circles and reported the XY position of each cylinder. They each measured x=-0.0001 and y=0.0002
            if I make one of the cylinders a datum in exact measure and look at the position or coaxiality of the other, it measures x=-0.0005 and y=-0.0035

            If i stick a 0.500 pin through the smaller hole, you can clearly see that it is not in the center of the larger hole.
            153010 Global Advantage w/ LSPX1H_T Analog Probe
            7107 Global Classic TP20
            2019R1 SP1 CAD++

            Comment


            • #9
              Making one of the holes a datum and relating back to the other hole will hose you with the " short " feature syndrome. Looking at the section 7.6.2.3 it sounds like you could make a set from all the circles and do a best fit alignment from them. Then position , like you are doing the lower level of a composite position. The straightness of a line method I talked about above I think would give you the same effect.

              Comment


              • #10
                I think ctw00 summed it up best. As per 7.6.2.3 of the Standard, this is allowed. I've just never tried it in PC-DMIS.
                CMMXYZ Applications Specialist: PC-DMIS Support and Training. Check out my PC-DMIS tutorial videos... https://blog.cmmxyz.com/blog/tag/cmm-tech-tips

                Comment


                • #11
                  While looking through the Hexagon Idea Center it looks like someone requested this feature, and it is included in PC-DMIS 2020 R2. https://hexagonmi.userecho.com/en/co...n-to-no-datums

                  Comment


                  • JacobCheverie
                    JacobCheverie commented
                    Editing a comment
                    It is included in 2020 R2, but it will not work if the two bores are of different size.

                Related Topics

                Collapse

                Working...
                X