Mark E. Foster, Applied Geometrics, Inc, President/GD&T Instructor/Mentor wrote on linkedin website--if I am not allowed to copy and paste, I will ask the administrators to delete my post---I am just trying to be helpful. I am not working for Mark, nor I am affiliated with his company--
Beginning of post from Mark E. Foster
""""""So, where is it written that we "must" use composite position to a set of multiple features of size? You "can" use the composite positioning tool for a set of multiple features of size, but I would not recommend doing so unless it is functional. The issue is that position (composite or not) is used on features of size and profile is used (mostly) on surface features.
But I think the gist of your question is really using the composite tool on multiple features versus a single feature. You could apply composite position to a single feature of size, but the effect would be to simply tighten the orientation tolerance on that feature, so you could have the same effect with a non-composite position and an orientation refinement feature control frame. (There are some "fancy" things that someone could do with regard to simultaneous versus separate requirements here, but let's keep the discussion simple -- at least at first.)
With Profile, I could use composite profile on a single surface, but again one would really be simply refining form and potentially orientation, depending on datum references. If the surface in question were nominally flat, I would recommend simply using a single-line profile for location and then refining orientation/form feauture control frames as necessary. If, however, the surface in question were a complex contour (or not simply flat), then the use of composite profile for a orientation/form requirement might be necessary. "
In re-reading through the Composite Position section of the 2009 standard, it is clear to me that the *intent* of the definition is for it to apply to patterns of features of size, thus it is clear to me that the *intent* is for it to apply to more than one feature of size at a time. However, if I put my lawyer hat on (as much as that hurts to do), the Composite Definition, or any other definitions in the standard to my knowledge, never clearly define what constitutes a "pattern." There is a lot of implication, but no definitive definition. So, one could argue that I could have a "pattern of one" feature of size. And, of course, we see people do that exact thing all of the time out there in actual industry. The same interpretation (i.e. orientation only) would be the way we would interpret a single feature of size with a Position feature control frame back to a primary planar datum feature only when only an orientation relationship exists between the planar datum feature and the feature of size in question, such as when we are going to use that feature of size as our secondary datum feature. i.e. The Position callout in that case would really only be serving as an orientation control.
So, traditionally, we have simply interpreted the lower tier(s) of a composite postion feature control frame applied to a single feature of size to be an orientation refinement for that single feature of size. And, as such, one could instead use a single-segment position for that feature of size, then follow it up with whatever orientation refinements we might need using separate orientation feature control frame callouts. And in the case of the secondary datum feature of size with a Position feature control frame (rather than just an orientation control), we would normally advise simply using an orientation feature control frame instead.
THEN, we introduce the concept of "simultaneous requirements." Since the simultaneous requirement default ONLY applies to Position and Profile tolerances, then there may, in fact, be a valid argument for using a Postion callout on what otherwise would ONLY be an orientation control, simply to force a simultaneous requirement with other features that are also Positioned or Profiled back to that same datum reference frame.
I'm not a huge fan of specifying things that way unless it seems like the only way to get things done. We sometimes find ourselves doing things because we *can* and not because we *need* to do them that way. I advise trying to find ways to make things as clear as possible without delving into the "tricky" ways to accomplish something within the standard. On the other hand, there are occasions where making use of this simultaneous requirements rule is very handy, and sometimes the only way to truly achieve the maximum possible tolerances for a given design.
While I know and respect Alex K's GD&T knowledge, the quote that you are using is from his Fundamentals-level text as well as his online resources. When I teach GD&T to people new to the subject, I also make a similar statement (i.e. that composite feature control frames are to be used on multiple features at a time, not just for one feature) because that IS the intent of that tool, and it is probably the best use of that tool. However, when we get into more advanced topics, we find ways to combine various tools (e.g. composite and simultaneous requirements) in ways that we may not have thought of when we were at a Fundamental-level of knowledge. The Y14.5 standard is intended to be a book full of definitions, rules, guidelines, language tools in general, that we are able to use in order to communicate effectively. So just as there are some people who just barely speak a language and there are others who have a supreme command of that language, we have to learn as we go to move from the former to the latter. """""""""""""""" end of post from Mark E Foster
