Worst case means variable ? -Resultant condition

[gabimo]

Y14.5-1994 question:

I am sure I miss something, but I don't know what:

1.3.23 Resultant Condition. page 3

The variable boundary generated by the collective effects of a size
feature’s specified MMC or LMC material condition,
the geometric tolerance for that material condition,
the size tolerance, and the additional geometric tolerance
derived from the feature’s departure from its
specified material condition.

Appendix A - page 199
Resultant condition is introduced and explained as
a worst case inner locus or outer locus condition.

 

[ewh]

Worse case is different for a stud than it is for the hole the stud is to go in.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[greenimi]

I don't know the answer, but let's say the question shows up on the certification exam -1994-:

What is RC:
a.) The variable boundary generated by the collective effects .............
b.) A worst case inner locus or outer locus condition.........................

The other options you could eliminate and does not have a AND b option


What would you do?

 

[CheckerHater]

According to 2009 it is both: the single worst-case boundary generated by the collective effects etc., etc., etc.
So I would wait for 2009 exam.

 

[3DDave]

I think you are wondering how it can be both Variable and Worst case?

The answer is the committee was not structured for workers on different sections to review each other's work. This introduced a number of conflicts, such as this one. In addition, they were adding definitions for cases that are of dubious value - such as resultant condition - for descriptive completeness. In this case, the Appendix writer's were wrong.

Looking at 2.11.2 and the associated figures 2-7 to 2-12 support that Resultant Condition varies based on the combination of feature 'actual mating envelope' (AME) and the affect the AME has on the available tolerance to describe the unreachable volume of the feature. For example - 2-7, External feature. The minimum size of the pin .29.5 and they subtract another 0.5 for position tolerance to leave 29.0, which is a diameter that would be perfectly positioned and still be inside the solid pin. Since it is inside the pin, it is unreachable.

The definitions flip for LMC. For no good reason they are not applicable to RFS.

 

[3DDave]

It's interesting that between 1994 and 2009 the committee saw fit to not only redefine terminology to be completely different in meaning, but add some new terms.

1973 - basis
1982 = 9 years
1994 = 12 years
2009 = 15 years

Extrapolating, the next version will follow an 18 year gap -> 2027?

 

[Belanger]

Keep in mind that appendices are not part of the official standard. So while a discrepancy is indeed strange, it's not a huge deal.
The definition of RC was changed in 2009 to be a worst-case constant value. So it's fun to talk about this in 1994, but they've cleaned it up so it's no longer an issue.

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

 

[3DDave]

It isn't 'cleaned-up,' just a new, incompatible interpretation of RC relative to the previous version. Which itself isn't new; the Y14.5 committees have flip-flopped a number of times.

 

[Belanger]

Well, good point. I meant that RC is now a constant value, although unlike VC it doesn't carry that constant over the full size range.
So it's constant because that's how they define it, not because of any inherent concept. Still a improvement, I would say.

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

 

[3DDave]

It does now. There is only one value for RC, just like there is only one value for MMB. in 1994 RC varied as the size of the feature varied, while VC was constant. Now no VC and no variation.

What was puzzling was the lack of utility of the concept for Resultant Condition. They spent a lot of effort on it for 1994 and then threw most of that away, but there's no reason given to even have it.

 

[greenimi]

[Keep in mind that appendices are not part of the official standard.]J-P,

Ref: certification exam:

Are you saying that you are not going to be tested from the appendix?

 

[Belanger]

What was puzzling was the lack of utility of the concept for Resultant Condition.

I wouldn't say that concept of RC has no utility. It is helpful in calculating some types of tolerance stacks (wall thickness), allowing one to side-step a full-blown spreadsheet method.

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