Composite GDT

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  • Composite GDT

    I have a part that has a composite callout for 4 holes as follows
    4 x .250 holes @
    .028 mmc to datums A,B,C
    .014 mmc to daum A
    Datum A is a plane
    Datums B,C are the edges of the part.
    these holes are centered and equally spaced 4 inches apart.

    The first callout is easy. The secondary callout is giving me trouble. I was told that the proper way to dimension for the secondary callout would be as follows:
    1. create a best fit line between two of the holes i checked.
    2. create a new alignment that will rotate to that newly created line
    and set my alignment zero to one of the holes i checked.
    3. dimension the holes with my new alignmet active.
    the results would be as follows

    cir1 X0.000 Y0.000
    cir2 X0.000 Y4.000
    cir3 X4.000 Y4.000
    cir4 X4.000 Y0.000

    I'm not sure if this the correct way to dimension these holes. The next part I have to check the holes are not inline so creating a line between them
    to rotate to would not work. I have seen a lot about best fit alignments on this message board.I was hoping someone could use my examble above and walk me through how to create best fit alignment or any way better to dimension my part.
    sigpic
    I got all the sweet hook-ups. Know what I mean Vern.
    pc-dmis version 4.3

  • #2
    Can you post a print for this? Are the (4) holes piercing datum -A-? If so, then the second FCF is a true position to this plane, -A-, which is like perpendicularity. Meaure the holes as cylinders, and then true position them to the plane.
    Steven69
    sigpic

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    • #3
      Yes that is the correct way. You are checking the bolt hole pattern to itself. aling thru two of the an origin of one of those, pretty simple
      sigpicSummer Time. Gotta Love it!

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      • #4
        Don do you have cad or are you checking without. I assume you do not. It would help if we could see the print. From what I see you have 4 holes each one having a positional tol. of 0.028mmc to datums b & c along datum A, and as a composite of all four together at 0.014 mmc to each other along datum A. The location I can not tell form B & C and 4 inches apart form each other. It would be very helpful to you to take a GD&T course. But we will always try to help you in any way we can. More information is needed. You could but in your profile what type of software you are using, Machine type and what windows program you are running it on.
        Last edited by pniven; 05-17-2008, 05:48 AM.
        sigpichttp://npmichaels.com/ (My sons book)
        THANKS (CAD IS ALWAYS MASTER)
        4.3 & 4.2MR2/GLOBAL/PH10MQ/WINDOWS XP

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        • #5
          if you are using version 4.0 of PCDMIS or later, you can have the software take care of the composite true position automatically. just go under the 'Insert' menu and then the 'Dimension' submenu and uncheck the 'Use Legacy Dimensions' box. Then go back to your program and try to do a true position. Inside the dialog one of the options will be a 'Composite' checkbox. Just build feature control frame to match your print and you are done. Like I mentioned earlier though, this only works after version 4.0.
          "I keep telling people it's all about credibility, but nobody believes me." -- Anonymous

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          • #6
            This is NOT the correct way to check the lower portion of a composite FCF. By rotating to two holes and translating to one, you are saying that these two holes are more important than the other two. Each of the holes share the same level of importance and function. They must be inspected as such.

            After checking the upper portion of the FCF, do a best fit alignment of the four features and reinspect them using the basics on the print. The best fit alignment will adjust or "fit" the pattern for the best results. NEVER align to the pattern itself.
            sigpic GDTPS - 0584

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            • #7
              [quote=inspector212;153862]This is NOT the correct way to check the lower portion of a composite FCF. By rotating to two holes and translating to one, you are saying that these two holes are more important than the other two. Each of the holes share the same level of importance and function. They must be inspected as such.

              After checking the upper portion of the FCF, do a best fit alignment of the four features and reinspect them using the basics on the print. The best fit alignment will adjust or "fit" the pattern for the best results.quote]

              WHS.
              RFS Means Really Fussy Stuff

              When all you have is a hammer - everything looks like a nail....
              sigpic

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              • #8
                I agree with inspector212 and will add this. The upper part of the composite FCF is the pattern-locating zone and the lower is the feature related zone. All feature axes must simultaneously lie within Both tolerance zone cylinders. See page 99 Fig 5-19(e) of the standard. I don't think PcDmis can actually do the latter and compare simultaneously. . .
                v2.1 then Hibernated from PcDmis
                v4.2 mr1 offline only now

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                • #9
                  Originally posted by 3d_guy View Post
                  I agree with inspector212 and will add this. The upper part of the composite FCF is the pattern-locating zone and the lower is the feature related zone. All feature axes must simultaneously lie within Both tolerance zone cylinders. See page 99 Fig 5-19(e) of the standard. I don't think PcDmis can actually do the latter and compare simultaneously. . .
                  If there is one TP symbol and two FCF's - then it's a composite tolerance and the above applies. If there are two TP symbols and two tolerances then it is not a composite tolerance and these should be evaluated as individual tolerances?

                  PC-DMIS v4.2MR1 has a checkbox for composite evaluation if that applies.
                  PC-DMIS CAD++ 2o19 R1 SP11

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                  • #10
                    Those are Single-Segment FCF's but I can't find in the standard any example with just the Primary -A- in the second FCF. They all use -A- and -B- and call out the simultaneous provision. My thought is that if you have the SEPT REQ next to the lower FCF you would then be allowed to position the pattern to itself using the horizontal BASIC callouts and the perp to -A-. I will look further in the standard and see if I overlooked it.
                    v2.1 then Hibernated from PcDmis
                    v4.2 mr1 offline only now

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                    • #11
                      as far as I understan the comp. FCF is that: the 1st FCF is using the datums, the other is to each other, so if you have 4 holes I would make one hole an orgin and dimention a hole to the left or right and above or bellow an than I would take the hole above or bellow and call it an orgin and dimention the hole to the right or left, that is still using the same alignment as for the 1st FCF
                      Last edited by MIKEY; 05-19-2008, 09:21 AM.

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                      • #12
                        Originally posted by inspector212 View Post
                        This is NOT the correct way to check the lower portion of a composite FCF. By rotating to two holes and translating to one, you are saying that these two holes are more important than the other two. Each of the holes share the same level of importance and function. They must be inspected as such.

                        After checking the upper portion of the FCF, do a best fit alignment of the four features and reinspect them using the basics on the print. The best fit alignment will adjust or "fit" the pattern for the best results. NEVER align to the pattern itself.

                        Dead on correct
                        sigpic.....Its called golf because all the other 4 letter words were taken

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                        • #13
                          Dead on correct
                          You are forgetting the simultaneous requirement to the Pattern locating zone.
                          v2.1 then Hibernated from PcDmis
                          v4.2 mr1 offline only now

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                          • #14
                            Originally posted by 3d_guy View Post
                            You are forgetting the simultaneous requirement to the Pattern locating zone.
                            I agree, especially if it truly is a composite callout (one TP symbol for two FCF's).
                            PC-DMIS CAD++ 2o19 R1 SP11

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                            • #15
                              Originally posted by 3d_guy View Post
                              I agree with inspector212 and will add this. The upper part of the composite FCF is the pattern-locating zone and the lower is the feature related zone. All feature axes must simultaneously lie within Both tolerance zone cylinders. See page 99 Fig 5-19(e) of the standard. I don't think PcDmis can actually do the latter and compare simultaneously. . .
                              Sure it can. If it lies w/in the larger PLTZF, and you best fit the pattern, and dimension that to the tighter FRTZF, why wouldn't that compare them both simultaneously? (if they are good to both segments).
                              Kev
                              RFS Means Really Fussy Stuff

                              When all you have is a hammer - everything looks like a nail....
                              sigpic

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