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greenimi,

In my opinion, your case[ ]1 is not fully toleranced. A positional tolerance to datum[ ]A of the .769/.755 dimension, would make it complete.

Case[ ]2 again, requires a positional tolerance applied to the .769/.755 dimension, as well as to the 1.092 dimension. The parallel tolerance applied to the .769/.755 dimension should only reference datum[ ]A, since the dimension is datum[ ]B.

In case[ ]3, you again need the positional tolerances.

If this were my drawing, my datum[ ]A would be the base of the part, and datum[ ]B would be the tapped hole. I would make datum[ ]C either the 3/4[ ]opening, or the clearance hole. I think this would be more meaningful, and easier to inspect.





JHG

I agree with drawoh about case #1. Replace the parallelism with position. Parallelism does not locate, it only orients.

Case #2: The datum B reference is not only incorrect, you gain nothing from it, which, by way of circular reasoning, is one reason it is incorrect.

Case #3: What drawoh said.

I guess I'm just providing confirmation on drawoh's post. I don't think I added anything to the thread.

Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
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Also, per the previous thread, it makes a difference if you're using the 1994 standard or 2009. In the newest standard, they clarified the relationship (basic location) between the datum feature simulators.

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

Okay, let's clarify. We are using 1994.

I did NOT understand that it's a difference from what we are talking about here. 2009 brings just a clarification (for the datum feature simulators) and not a change from this point of view (similar to the simultaneous requirement, was in 1994, but 2009 clarifies it!)
Am I wrong?

Also I have added another case--case #4-- to mimic the discussion from the thread I have mention above---

See the revised sketch I have attached.

Thank you again for your help

I believe that was my thread you are referring to. I stated in that thread that I, myself, was not recommending that particular approach. I did want to discuss with others what I found in investigating and studying the issue.
Case#2 is based on the same idea, but, what you have shown here is a much more conventional clearance situation where position at MMC makes functional sense. I agree with JHG on his framework.
Function is the important part in your tolerancing approach; my situation was a spindle shaft keyway where the mating key was ground to suit at assembly for a tight mating fit.
I would never advocate a single approach just because you think it "looks like" something else. Does it function the same way? I don’t care if it looks like a part shown in the book, does it work that way? This is exactly the problem with the examples in the book they need to show how it functions.
20 or so years ago, I wrote a company book, where I showed examples of our particular parts in the assembly, discussed the function and how it affected my choice of datums and my tolerance derivation calculations.
Frank

In case 4 you are expreesing a similar concept, but, does it fit the function of your particular part?
Frank

I kind of agree with you that the functionality is not here, but I am asking for academic purpose only--if scenarios--. Let's say, something, IF the function is case#1, does the GD&T looks "legal" and fully defined (the slot) or if the functionality is case# 2, how does the GD&T looks "legal" and fully defined and so on.
I am asking not realy from the "real" world, but more from the "academic" world.

Yes, I know that the real world should mimic the academic one, but I appreciate when you guys supporting a learning environment as I stated at the begining at this post.

OK, conventional methods are always the ones I would explore first, it just makes it easier, believe me. I am certainly in favor of learning, I was just worried about unlearning is all. My answer would be the same as in the other post, then.
Frank

While we were discussing the other thread and J-P, Dean and Evan seemed to agree that for Frank's example parallelism of slot side walls locates through the back door, I asked Jim Meadows, chairman of Y14.43 sub-committee "Dimensioning and Tolerancing Principles for Gages and Fixtures", the same question. And guess what... He clearly stated that parallelism never locates.

He said that for him the intent of the print was clear - keeping datum feature B inline with datum axis A, but unfortunately nothing on that print controlled such relation, means there was no trace of tolerance from which one would take 10% to define relationship between physical datum feature simulators A & B. So the slot B could actually be anywhere relative to A and still meet the print.

Well, pmarc, that would have been true under 1994. But it was pointed out that according to 2009 paragraph 4.5.2(c), the datum feature simulator shall (not may) have a basic location to the other simulators, unless the translation symbol is used.

So while I agree that the intent of parallelism was never to control location by the back door, the rigid requirements of 4.5.2(c) actually end up making that happen indirectly.

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

J-P,
Sorry if this sounds sarcastic, but what would be the amount of fixture tolerance defining mutual relationship (locational in particular) between centerplanes of datum feature simulators A & B if that fixture was going to be build?

Datums themselves have no tolerance, of course. But datum feature simulators are built to what we call "established tooling or gaging tolerances."

Regardless, that still doesn't avoid the black-and-white statements of 4.5.2(c).

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

pmarc,

One other detail that was brought up in the other thread, at least in some of my posts, was the unique geometric properties of a single slot with a single datum axis. The variation in the "aiming" of the slot can be described both in terms of orientation error or in terms of location error. The distinction becomes blurred, especially when we combine it with a compound datum feature that includes the considered feature itself.

So when Jim Meadows says that Parallelism never locates, we're not saying he's wrong. At least I'm not saying that. But I'm not sure exactly what Jim means by the word "locates" - I don't know if he pondered the issue as much as we did. One thing that we found in the other thread was that it was necessary to nail down exactly exactly exactly what "locates" means. In the end, my definition was that location is not controlled if the tolerance zone is allowed to translate relative to the datum reference frame.

The Parallelism control in Frank's example imposes a control that indirectly limits the amount of location error that is possible. This could be described as "back-door location" but it is achieved by the unusual condition of orienting the feature to a related actual mating envelope that includes the feature itself. But this back-door location is not location by the above definition, because the tolerance zone is still allowed to translate relative to the datum reference frame.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

Evan,
Let me put it straight. Each of us here are free to interpret meaning of the word "locates" in different ways, especially that it is not standardized by Y14.5, but as long as we do not agree that all 3 scenarios I sketched in Frank's thread meet the print specification, I will not say our understanding of this term in this particular situation is the same.


I presented exactly the same picture to Jim Meadows and received answer that not only those 3 cases are possible, but even much more complicated slot's configuration can occur and still meet the print.

All comes down to a question whether you agree with this or not.

Here is the link again:

pmarc,
I am honored you brought it up. I appreciate even more so that J-P, Evan and others took their time to really ponder it. Only you know how much thought James gave it. Your description makes it sound like a pretty conventional knee-jerk response.

Greenimi,
I think the discussion on this is helping to make the point on why it is safest to use a conventional method if at all possible.
Thanks guys,
Frank

pmarc,

It appears that we've exhausted all of the arguments related to the geometry itself. The question of whether or not all 3 scenarios meet the print hinges on whether or not the simulators must be basically located to each other. This comes down to how one interprets the implied basic zero, and whether or not it applies when no location control is specified. This becomes an issue of how interprets Y14.5, and the vague/inconsistent statements it makes on basic location - when it is defined and when it is not.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

"I appreciate when you guys supporting a learning environment"

I do to, unfortunately it is sometimes more complicated and people do not always agree. Even in the committee and after things are published people do not still always agree so I am not sure if I can provide more than, “don’t do this unless your looking for a fight”.
If I were doing it today (this was 1990) I would have suggested he consider using profile simply to avoid the whole orientation to locate issue. My reading of the 2009 standard and Mr. Henzold's book on the ISO certainly leaves me the impression of the trend is in the direction of allowing combinations of toleranced dimensions with profile as a refinement callout.
Frank

pmarc,
I had exactly the same reaction as Jim... After more thought and especially a hit over the head with a figurative 2 X 4 by Evan, I saw the light... I will see Jim in a about 4 weeks and will try to find a time to talk about this.

J-P,
'94 or '09 the concepts for datum feature simulators are the same with regard to the effect that make's Frank's assertion a correct one. Datum feature simulators must be "perfectly" located and oriented with respect to higher precedence datum feature simulators & that is not newly introduced in Y14.5-2009. The only addition provided in 2009 was the introduction of the translation modifier that allows a secondary or tertiary datum feature simulator to translate, rather than being fixed at a "perfect" location. Since there was no way to specify "moving" in '94 the only logical route (I believe) is that that secondary and/or tertiary datum feature simulators which can be located due to the capabilities of a higher precedence datum are required to be fixed in location.

Dean