Regular Feature of Size Example - Parallel Opposed Line Elements and Circular Element

[tmillik]

Hello, this is my first time posting so I am very interested in the responses I receive.
I am looking for a few examples related to regular features of size per the definitions in the 2009 and 2018 revisions of the Y14.5 standard.

One of the requirements is that the feature is associated with a single directly toleranced dimension. The second requirement is that the feature is one of the following: a cylindrical surface, a spherical surface, a circular element, a set of two opposed parallel line elements, or a set of two opposed parallel surfaces.

First I would like to see an example part that has a feature of size that is two opposed parallel line elements and an example part with a feature of size that is a circular element.

Second I would like to understand what the center for each of these would be. Would the center for two opposed parallel line elements be a line or a plane? Would the center of a circular element be a point or an axis?

Lastly, how would Rule 1 work with these examples.

I look forward to hear what some of the experts think.

Thanks!

 

[3DDave]

This is all covered in those versions of the standard.

 

[Burunduk]

tmillik, a circular element and a set of two opposed parallel line elements as features of size are not covered in ASME Y14.5 beyond their mention in the definition of a regular feature of size. So any useful interpretation is appropriate.

An example of opposed parallel line elements could be the two extremities of a round-ended slotted hole.

 

[tmillik]

Thank you for the responses. I've read through a number of threads on this forum related to features of size and I'm learning that the standard is lacking full definition in a few areas. It definitely makes things more difficult when multiple interpretations are possible.

 

[3DDave]

If you say there are multiple interpretations, you must have examples.

 

[tmillik]

This is all covered in those versions of the standard.

As Burunduk stated, opposed parallel line elements and a circular element as a regular feature of size is only mentioned in the definition for a regular feature of size. There are no specific examples showing these types of features.

If you say there are multiple interpretations, you must have examples.

Again, there are no examples of these types of regular features of size in the standard. Burunduk pointed out a good example of the extremities of a round-ended slotted hole. A possible example of a circular element as a regular feature of size could be the bottom of a full radius groove around a shaft.

I still have many questions related to these features. I imagine it would be very difficult to establish an unrelated actual mating envelope for one of these features. I could see being able to find a related actual mating envelope if the feature was used as a secondary or tertiary datum.

The lack of definition and examples beyond the regular feature of size definition in the standard leads me to believe that others may have similar questions (specifically about opposed parallel line elements and a circular element). Leaving it open-ended will result in different interpretations

I feel like I may be opening a can of worms.

 

[Burunduk]

tmillik, here's an interesting example of two opposed line elements treated as a feature of size and have position tolerance applied to them, to control the location of a drafted slot:

Slots with draft

Also, on another thread here ( thread1103-474434 ) I recently posted an example of two opposed circular elements (the edges of the recess) treated as FOS. Waiting for opinions in that one:

recess edges

 

[3DDave]

This worm can you think you are the first to open is simply a recognition that the committee was flawed in their creation of this flawed document and there is no amount of arguing that can time travel to fix it.

However, making claims that there must be some outcome is not the same as presenting those outcomes. If you have multiple interpretations, present them so that in 50 years or so some future committee might then address them. The past groups have worked hard to create more problems since the 1994 version with no sign of changing course, but maybe one day a future group will.

For example: 2009, 7.4.5 Noncircular Features of Size lists "elongated holes." It's the only mention of that term in the document. Elsewhere similar features are "slotted holes" although normal English calls them "slots." The members love adding embellished but uncoordinated vocabulary, such as what you refer to. Which means the "round end" and "slotted hole" features are entirely different.

Once one departs from belief in straightforward interpretations and veer into the often contorted and incomplete definitions that have exploded in the last 3 version, all bets are off. This is largely a function of replacing the original concepts of hard-gaging to check parts with the ingress of CMM software sales efforts. So many concepts have been added that make sense only in CMM schemes and do not have real-world functional implementations.

Welcome to the worm can.

 

[tmillik]

3DDave,

At no point did I try to claim that I am the first person to open this can of worms nor am I here to argue. I was simply looking for the opinion of other professionals.

Burunduk,

The examples you have provided are very interesting. I am going to study those for a bit. Thank you for being helpful.

 

[Dean Watts]

tmillik,

I'd just like to say that your questions are good and valid. I think Burunduk's responses address your questions well.

The definition of feature of size should be both simplified and improved. It needs to a be a definition, rather than a list of examples. My personal opinion is that irregular feature of size is an unnecessary term. I would prefer that a feature of size be defined well, and features of size that have interruptions, but which still function the same should be explained well, including their limits of size.

Dean

http://www.validate-3d.com

 

[3DDave]

That tapered slot example certainly solves a "how to inspect this" problem, but it does a poor job of describing the fit with the mating part. It fails to consider the mating part variation and appears to try to borrow datum target techniques to create a feature of size definition. Look at the virtual condition** allowed by the combination.

Great - put that in the standard so there is a common understanding of what that means and can literally be standardized.

The question is "Why did the committee overlook a term mentioned in one sentence throughout the rest of the document?" There are a lot of them.

"I feel like I may be opening a can of worms." means - the can has not been opened before. It's your own statement.

**This will no doubt cause a problem for Burunduk because the standard re-defined "virtual" to have a specific, very limited, meaning, but I know no other English word applicable to describe "what it appears to be but only by considering all possible variations so that there won't be a case where the part meets those limits, but instead this is the apparent sum total effect of all limits as if they could simultaneously occur."

Since I don't care to type that out every time just keep in mind that I will preface any cases where I am specifically using the limited ASME Y14.5 definition as in, "per the ASME Y14.5 limited virtual condition" which basically means "subtract/add this number to that number."

 

[Burunduk]

That tapered slot example certainly solves a "how to inspect this" problem, but it does a poor job of describing the fit with the mating part.

The example doesn't do a poor job of describing the fit with the mating part, because it doesn't attempt to do so in the first place. The example could be expanded and improved by showing how the part and the mating part fit together, including the dimensioning and tolerancing scheme of the mating part, but even as it is the example is pretty detailed and informative, especially considering it is available for everyone for free online.

I know no other English word applicable to describe "what it appears to be but only by considering all possible variations so that there won't be a case where the part meets those limits, but instead this is the apparent sum total effect of all limits as if they could simultaneously occur."

I would recommend using the more general term "worst case boundary" for that purpose.

 

[3DDave]

I am sure you would, but that is also already defined to a different purpose. We've discussed this before and you have been unable to deal with conditions that aren't resolved by add/subtract this from that.

 

[Burunduk]

Actually, there is no unique definition for "worst-case boundary" in Y14.5. It is acceptable to use this term for any type of boundary generated by the collective effects of different tolerances. Virtual condition, on the other hand, is specifically associated with a geometric tolerance applied at MMC/LMC, accounting for the relevant limit of size for the feature and the value of the single geometric tolerance that corresponds with that limit of size. Virtual condition is a special case of a worst-case boundary. What you describe is a different type of a worst-case boundary.

 

[Dean Watts]

This may not be directly helpful for the topic, but I thing the world would be a better place if MMB and LMB were expanded to all features. I think we could then get rid of the terms virtual condition, resultant condition, inner boundary, outer boundary, and worst case boundary. Simpler is always better in my opinion.

Dean

http://www.validate-3d.com

 

[3DDave]

While the committee has their own narrow view, it is generally applicable that a virtual condition** for a feature depends on the basis from which that is determined. "worst-case boundary" is applied in the standard to the addition/subtraction of two numbers, which is not the case I described.

**This will no doubt cause a problem for Burunduk because the standard re-defined "virtual" to have a specific, very limited, meaning, but I know no other English word applicable to describe "what it appears to be but only by considering all possible variations so that there won't be a case where the part meets those limits, but instead this is the apparent sum total effect of all limits as if they could simultaneously occur."

Again.

 

[Burunduk]

"Worst-case boundary" is used in the 2018 standard to describe every type of boundary. As I said it's a general term, and the accepted meaning is a generated boundary resulting from the collective effects of different tolerances. Whether the calculation is done by addition, subtraction, or other operations - that's irrelevant. Each "Virtual condition" is always related to one specific non-RFS geometric tolerance and single size tolerance. But why use the correct terms when you can be unclear and confusing to others? As long as you don't let yourself be confused by the facts that's OK.

 

[3DDave]

Every boundary? Even when a different DRF is chosen that the original definition did not include any feature of? You know the case of changed DRF - what I showed was in error in the standard with clear mathematics that you did not seem to understand.

Size + tolerance (+ sometimes bonus, though it is part of tolerance) can only be added or subtracted, which is exactly what every type of Y14.5 boundary is given as. What's relevant is that all of geometry understanding is not confined to those two operations.

I said if I would use the definition you prefer I would indicate it was the Y14.5 definition.

Nothing new comes from rote recitation. The standard is a flawed attempt to cover a subject, not a religious text that is handed down in universal perfection from a higher power. Don't confuse one for the other.

My definition and usage is a superset and encompasses the artificially narrow cases in the standard, but also recognizes the general case. I can neither help nor do I feel particularly constrained that the committee is so restrictive of what the word means, nor does your admonition affect that opinion. Anyone who is confused by that needs to learn how to think through the problem for themselves rather than being copy-paste robots.

 

[Burunduk]

Had you used the proper terms, you wouldn't need to clarify whether you use them per the standard's definition or with some other meaning. If you come up with a concept of your own not covered by the standard, describe it with terms different than those with an already established and different meaning.
Otherwise accept that if "worst-case boundary" is used in the description of several different Y14.5 boundaries, and there is no separate definition for this term, it could as well be used to describe tolerance-generated boundaries not covered in the standard. This is regardless of the arithmetic operations used for their calculation.
The standard may be flawed, but it does provide its users a technical language for effective communication. Abuse this language by using terms not as they are intended to be used, and you get incomprehensibility. It contributes nothing to thinking through the problem.

 

[greenimi]

Guys,

Can the "average users" get something from this discussion beside of you two yelling at each other?