Unclear on the meaning - Help

[ryandias]

I have received a print with a Flatness tolerance attached to the Datum. As far as I know this is backward, or am I missing a second meaning or interpretation?

I generally see datums attached to a GD&T tolerance.
See attached image.

 

[pmarc]

ryandias,
This is not according to any GD&T standard I am aware of, but I suppose the meaning is the same as it would be when the symbols were correctly applied.

 

[KENAT]

It looks hand drawn, otherwise I'd suggest it might be an issue of the CAD system not doing what the drafter wanted - or at least the drafter not knowing how to do it.

Like pmarc I'd guess it means the same as if properly applied, I certainly don't remember seeing anything like that in ASME Y14.5M-1994.

However, as always, if in doubt ask. Can you get in touch with whoever gave you the drawing, or even better who created it?

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[ryandias]

I will ask, the answer just won't be timely. I just wanted to confirm what I thought already.

 

[ewh]

Isn't flatness a GD&T tolerance? Isn't the datum attached to it?
While placement may not be entirely correct per the '94 or the current dstandard (it is reminiscent of the '82 standard), I think the meaning is clear and have often seen datum surfaces with such requirements. Either way, it means that the indicated surface is to be flat, and is datum A. I do not see how it could make any difference in interpretation from how the standard would recommend it be called out.
If in doubt, what other interpretation could you give it?

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[Belanger]

I agree with ewh. It's not precisely the standard's way to attach a feature control frame to the feature, but we can easily interpret the meaning. Might not be worth rocking the boat unless they were about to revise the drawing anyhow.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[ewh]

That is what I was thinking, especially if it is a customer drawing. It may not reflect well.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[SteveMartin]

A properly phrased question rarely reflects badly. It does happen, but I wouldn't let the fear of a bad reflection stop the asking.

Having said that, I don't see the tolerance in question as ambiguous. I'm pretty sure I've seen drawings marked in just this manner before (though not at my current employer, so I can't go dig one out to check).

 

[ewh]

It does meet the '82 standard, with the exception of no dashes before and after the datum letter.

Generally speaking, I agree about asking questions. Properly phrased, there are no stupid questions, especially if there is a possibility of multiple interpretations. However, this is not a perfect world, and depending on the demeanor of the customer, it may be inferred that this shop does not have a good grasp of the applicable standards. If they question this callout, what are they going to do with a true position of 0 @MMC? Or any of the multitude of easily mis-interpreted principles of the standard? It is one thing to ask about something that could be easily mis-interpreted, but this is more akin to pointing out a minor spelling mistake that would have no bearing on drawing interpretation.
If you have been retained to also review the drawings for mistakes, then point it out and ask for clarification. Otherwise, is it really worth the risk of putting your organization in a poor light (and using customer time) for something as inconsequential as this?

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[KENAT]

However, what if the customer does mean something different by this slightly non standard representation.

How bad does making a bunch on non functioning parts look?

I'll back Steve on this one, in this case you'd perhaps phrase the question in such a way as to indicate you think they mean the same as standard notation, but you just wanted to be sure.

Hell, if someone pointed out a glitch like this I'd me more likely to think they might understand 0 @ MMC.

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[ewh]

OK, you convinced me... If asked as a confirmation, there should probably be no problem.
I'm still scratching my head on what (anything) else it could mean, but I do admit that it is usually folly to assUme something on a drawing.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]