Datums

If its clear what surface is being referred to, there is no issue in showing it in a detail/section view. That does not by any means dictate that it refers to only part/half of the surface/feature specified unless it it accompanied by one of several notations to designate otherwise (ie: chain line, limited area/length, datum target, etc...). If you go by Y14.5 there are many examples of such a practice, one of them is below. I don't think the story is any different with ISO.

ozzy1,

So far, I agree with chez311. Can you show us a picture of what you are disagreeing with?

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JHG

I've never seen a problem with putting a datum on a cross section view or ever heard anyone say that the datum only consisted of half the surface.

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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.

Attached are the pictures of sheet 1 and 2. It is my view that the call-outs in question should be detailed on the side view (3rd view down) on sheet 1 not on a cross section on sheet 2.

It seems pretty clear what is being referred to as datum feature A. I see no reason why it MUST be on the side view - it comes down to personal preference.

To be sure, specification of a datum feature on a section/detail view does not change what that datum feature looks like or how it is established - the same as a diameter tolerance on a section view does not imply it applies to only half the diameter. Indeed a section view is sometimes the only way to properly show a particular feature.

Okay gentlemen I stand corrected.

Thanks

ozzy1,

Good drafting is a lot like good writing. Closely related information should be grouped in close proximity. Most of the GD&T is on the section view on sheet[ ]2, making it good place to call up the datum feature. The drawing has not been the way I would have done it, but I can make sense of it.

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JHG

I think some European? practices (ISO??) prefer holes called out in sections?
Frank

ozzy1,

What standard is this subject to - is it ISO? I see a redundant flatness callout, perpendicularity applied to a center line instead of the feature or diameter dimension, and *several questionable symmetry specifications without datum feature references and also applied to hole axes. None of these is really acceptable in ASME (except for the redundant flatness - this would be more like poor practice), but perhaps the story is different in ISO.

*I realize now these are not accompanied by a tolerance value for a geometric tolerance. It seems I've seen this someplace used in a similar manner, but I confess I'm not sure exactly what its meant to communicate. Implied symmetry of the hole location about an implied datum feature - perhaps the reamed hole between them? This combination of symmetry and +/- directly toleranced location of a feature has no meaning in ASME and I'd be skeptical it does in ISO - to my knowledge both documents recommend against +/- tolerancing of feature location as it is. Do you have an internal document to support this use?