To be more accurate, Dave, they're not shown at all. Does that, then, mean that they have to be perfectly located, or is it an incomplete drawing (See 1.1.4 Figures)? (Note also that the datum features are not indicated on the image... what horrible implications that may lead to!) Many people read too much into the absence of something in the figures and don't consider that the figure is cited as a specific illustration to a specific point being made in the text.
Please, Dave, list for us some of the examples you suggest are in the standard wherein "locations" of features of size are controlled by +/- tolerances.
I've taught a number of people, including several other instructors, who initially held a similar perspective to yours. Many think that "preferred" and "should", etc. give you carte-blanche to do anything because it isn't specifically precluded. Those who have worked to establish voluntary standards know that those are about the strongest words that can be used outside of a federally mandated standard. Federal standards can use the words "shall", "will", "must", etc. as specific directives, but
voluntary standards cannot because they have specific meaning under the law. ASME produces voluntary standards in that you are free to adopt them, and there is typically no specific legal action (other than contractual and civil liability) for twisting them out of shape. I understand that many companies have done /are doing /will do it as you endorse, however that is not supported in the Y14.5 standard or any other published standard, voluntary or mandated. Just because some people drink & drive without having had a terrible incident, it doesn't mean that it's acceptable or appropriate. Society moved beyond acceptance of DUI, hopefully industry will accept that GD&T has some distinctly right and wrong methods, per whatever standard is adopted.
Jim Sykes, P.Eng, GDTP-S
Profile Services
TecEase, Inc.
