Composite Positional Tolerance

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  • Composite Positional Tolerance

    Can anyone tell me how to do a Composite Positional Tolerance in PC-DMIS? Our LK-DMIS has a Composite Positional Tolerance function in it, but I cannot find it in PC-DMIS.
    I have some engine exhaust manifolds that have a Composite Positional Tolerance on the hole pattern that I need to tolerance.
    Please see attached drawing for reference.
    I have seen other posts on this question before, but I never did see a clear answer. Any help anyone can provide would be appreciated.
    Thanks.
    Attached Files

  • #2
    i think all that is saying is that the tolerance zone for the group of holes has to be perpendicular to datum -A- within 0.5

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    • #3
      You do not have a composite FCF.
      You have 2 single segmented FCF'S
      They are different.
      Kev
      Last edited by kbotta; 03-01-2006, 12:10 PM.
      RFS Means Really Fussy Stuff

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

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      • #4
        I believe you go into alignments, use "BestFit" call out your 8 diameters and you will get a best fit alignment for these features or what i belive is your "Composite Position" and report the 8 diameters again with your new tolerance. When you are done recall your original alignment.

        BS
        Windows 7
        Pc-Dmis 2015
        Global Performance 7-10-7


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        • #5
          Check those 8 hole's to the related datum reference frame shown in the FCF. Additionally, as Winston said, the second segment is controlling the orientation (Perp) of those tolerance zones relative to a primary datum (A).
          Last edited by kbotta; 03-01-2006, 01:42 PM.
          RFS Means Really Fussy Stuff

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

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          • #6
            All the print is asking for is the perp. of each hole to [A].
            James Temmen

            There is no job so simple that it can't be done wrong.

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            • #7
              Originally posted by J Temmen
              All the print is asking for is the perp. of each hole to [A].
              This is a highly sophistimacated dowaky, if you don't treat it responsibly... KABLAMO!!
              James Temmen

              There is no job so simple that it can't be done wrong.

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              • #8
                I believe if this was a single diameter it would be perpendicularity. But isn't this a pattern or group? Isn't this call out goverening the smaller positional tolerance for each feature within the pattern (feature to feature relationship) orientation as well as perpendicualrity?

                BS ???
                Windows 7
                Pc-Dmis 2015
                Global Performance 7-10-7


                Comment


                • #9
                  Actually, maybe I mis-represented myself.
                  1st, I would dimension the holes to the DRF in the FCF(top segment). Even though they are a pattern, individualy check them to the DRF. The tolerance zones are locked here, to the shown DRF.
                  THEN (bottom segment) I would best fit the holes (2-D), as the basic dimensions between each other apply, while the tolerance zone is restricted to -A- and inside of the confines of the larger PLTZF tolerance zone. The pattern could skew, and rotate, but not tilt, as the the tolerance zones are free from 2ndary, and tertiary requirements. Also, the holes must lie in the 2 zones simultaneously to be valid.



                  So, If you had a functional gage it would have:
                  8 pins at 10.14 with a DRF of A Y Z (I don't want to get into the whole RFS thing). That would mean the part would be locked in it's 6 degrees of freedom, and the pins (or stabs) would be located from the datum ref. frame.

                  For the bottom segment:
                  You would have 8 10.4 pins mounted on a plate. the part must fall over all pins and rest flat on the plate. It would not be confined to a complete DRF, just -A-. The part would need to pass both gages.

                  There, I think that makes more sense.
                  kb

                  ( IMO This should have been shown as a composite, not a 2 SS FCF.)
                  Last edited by kbotta; 03-01-2006, 01:57 PM.
                  RFS Means Really Fussy Stuff

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

                  Comment


                  • #10
                    Composite tolerance explanation

                    When dealing with composite tolerances, the easiest way to look at it is they want either the feature, if done as a stand alone, or the set of holes be relative to themselves within the specified tolerance. Addition of datums reduces the degrees of freedom you have to "float" or "bestfit" the pattern. In your case, the first tolerance locates the holes relative to the datums, the secondary (usually a smaller tolerance), locates the holes to themselves, without allowing Datum -A- to float! I just 2D besfit the holes and reprint them out with the .50mm true position. I hope this helps!

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                    • #11
                      Check out ASME Y14.5M-1994 section 5.3.2.1 paragraph b.
                      Last edited by tlnzz; 03-01-2006, 03:19 PM.
                      PC-DMIS V3.5 MR1. CAD++
                      Global Image 574.
                      Windows XP
                      ASQ-CMI. - 1986
                      Journeyman machinist, August 1970.

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                      • #12
                        Thanks for all the replies. Sorry I haven't checked in sooner.

                        Winston, JTemmen,
                        The callout that I am asking about is not a perpendicularity, it is a Composite Positional Tolerance of a pattern of holes (8 in my case).
                        Please refer to ASME Y14.5M-1994 like tlnzz states.

                        kbotta, KennyG
                        Thanks for the explanation and recommendations.
                        However, our LK-DMIS software, which has this function built in (hint, hint Wilcox), provides one result for this Composite Positional tolerance. The way you describe would provide 8 different results. Maybe the worst case would the actual result?
                        I'll give it a try though and maybe try a Best Fit on LK-DMIS for a comparison.

                        Does anyone else have any ideas?

                        Time to vent now. Attention Wilcox.
                        I don't understand why our newly released PC-DMIS 3.7 MR3 does not have this feature built in, but our 5 year old LK-DMIS software does.
                        Since it is a GD&T tolerance included in the ASME standard, PC-DMIS should be have the capabilities built in.

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                        • #13
                          My mistake, sorry. It would be a 2D best fit, rotate and translate only about [A]'s axis, then true position each hole again.
                          James Temmen

                          There is no job so simple that it can't be done wrong.

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                          • #14
                            Don't know if this will help but...
                            Last edited by JamesMannes; 08-03-2007, 09:27 AM.
                            sigpic

                            James Mannes

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                            • #15
                              James Temmen
                              No problem. Thanks again for the reply it sounds like the concensus is to do the Best Fit alignment and re-tolerance each hole like you said.
                              I'll give it a try.

                              James Mannes,
                              Thanks for the attachment. It says to do the Best Fit also and re-tolerance each hole also. Where did you get that information? It looks like it came from a training manual. If so, can you tell me where you got it from?
                              Thanks.

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