"half" dimensions
"half" dimensions
(OP)

What fundamental rules suggest that ‘half” dimensions are implied, as specified in the attached document?
Might be multiple rules combined and I would like to know them.
Not disagreeing, but I would like to get the details.





RE: "half" dimensions
The drawing looks symmetric, and there is a centre-line implying symmetry. Also, note how the secondary datum is a feature of size. It defines the centre. This is the only possible interpretation of the drawing.
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JHG
RE: "half" dimensions
Thank you for your answer.
Just to resolve my “work argument” what are the written ASME Y14.5 rules to reflect what you just said (symmetry)?
Thank you for your help
RE: "half" dimensions
RE: "half" dimensions
Is that the only Y14.5 rule needed to put the argument to rest forever, or I might need more "hidden" (not so obvious/ subtle) rules?
RE: "half" dimensions
I don't think you need something else (besides proper understanding of the rule, which in reality quite often is not well understood).
Do you have any specific scenario in which you feel this "implied basic zero dimension" rule does not fully work for you?
RE: "half" dimensions
I have nothing against FOS missing a half dimension. In fact, that's the only way to do it.
But locating dimension is different from size dimension. Implied zero is the real thing, while the implied symmetry is not.
Could anyone provide the reference, what are the fundamental rules behind the way dimension 60 is applied?
(See enclosed picture as well)
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: "half" dimensions
Fundamental rule 1.4(k) in Y14.5-2009 does not state anything about symmetry.
John H. Dunten, CD
Certified Drafter
RE: "half" dimensions
You pointed out a sort of inconsistency between wording of para. 1.4(k) and para. 2.1.1.4. Please notice that 1.4(k) does not say about "implied basic ANGULAR zero dimension", but "implied zero basic dimension", which may actually include both, angular and linear 0 basic dimensions, even though the paragraph refers to para. 2.1.1.4, where only basic angular dimensions are discussed. (FYI, it has been slightly improved in the draft of the future version of Y14.5).
If that does not convince you, I would like to ask you (or someone else) following question:
If zero basic linear dimension is not implied per 1.4(k), then why is this dimension not shown in fig. 7-56 in Y14.5-2009 (and in many other figures in the standard)?
CH,
I am looking at fig. 4-33 in Y14.5-2009, and I would say the if on your sketch design intent is to have both slots disposed symmetrically on both sides of the datum center plane A, you do not need the red dimension. With that being said, in order to avoid confusion I would use two basic half dimensions instead of one.
RE: "half" dimensions
I am glad we both agree that possibility for confusion still there. Standard provides the picture but not strong textual support.
It is interesting that even when center plane is a datum, you rarely see it used as origin for dimensioning.
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: "half" dimensions
Also, many of the higher level concepts are supported by more basic fundamental definitions. Datum center planes established from width features used to define symmetrical relationships can be confusing for this reason. You have to understand several basic concepts to build into the "whole" understanding.
Certified Sr. GD&T Professional
RE: "half" dimensions
Curious, Diego
RE: "half" dimensions
Certified Sr. GD&T Professional
RE: "half" dimensions
Yes, the rule was not explicitly spelled out in the '94 edition of the standard, even though it was widely used throughout industry (again, there are many figures in the '94 book where it is understood that implied basic zero linear dimension applies).
This could be one of the reasons why the committee decided to add this new rule to the '09 edition. Unfortunately, in my opinion, they did not do the job 100% correctly. There should have been 3 fundamental rules for implied basic dimensions. Two for angular dimensions - 0 and 90 degrees, and one for linear 0 dimension.
RE: "half" dimensions
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: "half" dimensions
http://www.eng-tips.com/viewthread.cfm?qid=377093
Is the answer "the same"/ still applicable?