ISO envelope applications 1

[Evom]

I've read in to the past week about the envelope boundary application when used as default for a drawing. I have multiple resources for placing together as much as possible for different scenarios other than ISO standards (1101). Right now I use mainly Alex Krulikowski's ISO Geometrical Tolerancing Reference Guide which does a good job for the most part but some details are lacking.

A few questions I have in regards to straightness and perpendicularity with the envelope boundary used:

From what I understand in regards for straightness for a feature of size (FOS) the envelope boundary is negated even if specified on the drawing and the extreme boundary from RFS is used instead. From another miscellaneous source it's stated that if straightness is called out for a non-cylindrical FOS, then it controls the median plane and not line like it would on a surface; is this true?

For perpendicularity, I don't see the FOS exception @ RFS for negating the envelope boundary; likely because it is an orientation control and not form. So if the size is at full MMS locally with the envelope boundary in effect @ RFS this means the boundary is completely filled and that the orientation must be perfect I presume as well?

If it's not, then it would orient the FOS out of it's envelope boundary theoretically speaking is how I understand it.

Any feedback is appreciated, thanks.

 

[CheckerHater]

First, let's straighten out some confusion: in ISO envelope boundary application IS NOT used as default for a drawing. Period.

You are stating several unnamed sources, beside Alex Krulikowski's ISO book. Are those OTHER books based on ISO or other standards?

Straightness requirement does not affect envelope boundary, but envelope requirement must be met nevertheless, due to Independence principle.

Straightness controls all linear elements of the surface, or axis, or derived median line, but NEVER the plane. Straightness does not control the plane.

Perpendicularity specified at RFS controls median line. Perpendicularity specified at MMR is a collective requirement and controls the boundary.

It would be better if you verify:

1. Are you working under ISO standards?
2. What are the other unnamed sources you are using?
3. Your terminology: for example, when you mention MMS do you mean part actually being at MMS, or (M) specified in feature control frame?

Some sketch of the situation that is giving you hard time always helps.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[Evom]

Sorry if the original post was confusing.

The ISO envelope requirement (invoking the envelope boundary) for my company is called out on all drawings, hence why I stated "when used as default."

According to Alex's reference book, when using straightness on a feature of size (FOS) he states "Where a straightness tolerance applies to a FOS, it controls the deviation of its median line. Where straightness applies to the median line of the FOS, the envelope requirement does NOT apply even if it is indicated on the drawing. The extreme boundary is calculated by adding the straightness tolerance to the MMS of the FOS".

Basically I understand this to mean that since straightness form does affect the overall size for a FOS by way of the median line control, it would contradict having the envelope boundary in effect thus it is negated for FOS scenarios only when using straightness.

The terminology used is directly from Alex's reference guide. MMS refers to Maximum Material Size which is a dimension defining the maximum material condition (MMC) of a FOS. Maximum Material Requirement (MMR) is the modifier placed in the tolerance frame.

Other sources other than ISO standards are ASME books where applicable for applications that have the same definition of control between both systems.

Thanks for your response.

 

[CheckerHater]

OK, I got you.

But be careful using ASME books to interpret ISO standards

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[pmarc]

Evom,
As far as I see, the questions you asked in this thread have not been really answered yet, so allow me to throw my 0.02$.

According to Alex's reference book, when using straightness on a feature of size (FOS) he states "Where a straightness tolerance applies to a FOS, it controls the deviation of its median line. Where straightness applies to the median line of the FOS, the envelope requirement does NOT apply even if it is indicated on the drawing. The extreme boundary is calculated by adding the straightness tolerance to the MMS of the FOS".

I do not have Alex's book, so can't verify true context of the quote, but if by any chance he meant straightness tolerance at RFS applied to a FOS, as unbelievably as this may sound, the underlined part is incorrect. In ISO, unlike in ASME, the envelope requirement will not be overriden in this case. The extreme boundary is equal to MMS of the FOS. The straightness tolerance value is not added to the MMS. It would be added if the envelope requirement was not indicated on the drawing.

For perpendicularity, I don't see the FOS exception @ RFS for negating the envelope boundary; likely because it is an orientation control and not form. So if the size is at full MMS locally with the envelope boundary in effect @ RFS this means the boundary is completely filled and that the orientation must be perfect I presume as well?

If it's not, then it would orient the FOS out of it's envelope boundary theoretically speaking is how I understand it.

If a FOS is fully at its MMS, meaning that the envelope boundary is completely filled, the orientation of the envelope does not have to be perfect. Actually, it can be at any angle to a datum, and that is why you apply perpendicularity tolerance to limit that orientation error.

 

[CheckerHater]

In ISO, unlike in ASME, the envelope requirement will not be overriden in this case.

It sure will be in "before 2010" ISO. (Alex's book is based on ISO 1101:2004 and companion standards)

Pmarc, if you are still around, I would appreciate reference to latest "after 2010" standard that changed it.

Looks to me that it is one of murky areas that need clarification.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[pmarc]

It sure will be in "before 2010" ISO. (Alex's book is based on ISO 1101:2004 and companion standards)

I know you asked for a reference first, so I owe you the answer (see below), but if you are sure it is in "before 2010" ISO, can I ask you the same? Which ISO standard states that the envelope requirement will be overridden by straightness at RFS applied to a FOS to control extracted median line?

And the answer to your question is following:
Just yesterday, after I had noticed this thread and the quote from Alex's book in particular, I searched through the ISO standards for a confirmation that it was correct. I found nothing (perhaps wasn't looking good enough), so I e-mailed Henrik Nielsen, the chairman of the ISO GPS TC213 committee, and asked him following question:
"ISO drawing similar to Fig. 5-2 from the Y14.5-2009 with additional (E) modifier specified. Assuming that all actual local (two-point) sizes are 16.00, is the feature of size allowed to have 0.04 extracted median line straightness error?"

His answer was following:
"In short, no, the two tolerances cannot "see" each other, so the envelope is always Ø16, independently of the straightness tolerance and the straightness tolerance is always 0,04 regardless of the size. This means that there are some combinations that are impossible, so if the two point size is exactly 16 everywhere, the median line has to be perfectly straight. Not because of the straightness tolerance, but because of the envelope requirement. The straightness tolerance only becomes an additional constraint, as the size gets smaller. So if it is a perfect, bent cylinder, it has to be Ø15.96 or less to take full advantage of the 0,04 straightness allowance."

I know it is the opinion of one recognized expert against the opinion of the other recognized expert, but in this case, with all due respect to Alex, I am with Mr. Nielsen. There is no such thing in ISO like exception to the envelope requirement. If a particular requirement is specified on the drawing, like the envelope requirement for example, it has to be met independently of other requirements. Or putting it differently, if you want to have the envelope requirement overridden, simply do not put (E) modifier on the ISO drawing.

This is the option that does not exist in ASME (should I say unfortunately?). In ASME, regardless of whether you apply (I) modifier to a FOS dimension or not, the straightness toleranced applied to the FOS always overrides Rule #1. There is currently no direct way to control straightness of the DML at RFS within the envelope defined by Rule #1.

 

[CheckerHater]

Thanks a lot, pmarc.

This was my impression first; if you noticed, I stated "Straightness requirement does not affect envelope boundary, but envelope requirement must be met nevertheless, due to Independence principle" in my Feb. 2 post.

Then I started digging thru my (very limited) resources and found some funny stuff.

First, look at reference from "old" ISO 8015:

http://files.engineering.com/getfile.aspx?folder=3f075ad7-4420-46b1-a42e-eb3e91b71f09&file=8015.png

Yes, it is about "local sizes", but here comes the funny part.

The part size is identified as DIA 150 h7, and according to the "old" ISO 286, this automatically invokes the Taylor principle AKA "Rule 1", and it was like that all the way 'til 2010:

http://files.engineering.com/getfile.aspx?folder=039d94a7-2185-47a4-ac84-1458aa5791e4&file=286.png

Yes, the mentioned version of 286 came out in 1988, but then both standards co-existed for over 20 years, and someone laying two books side-by side could easily come to the conclusion that Envelope requirement could be overridden as well. After all, if ASME has this rule, the idea may have some merit?

The new "GPS-ed" family of standard should clarify this one way or another, so I was asking if you have latest and greatest reference. You did, so I star your post.





"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[pmarc]

CH,

First of all I apologize for slow response and thank you for answering my question and appreciating my previous reply.

I understand your point, and agree that one could think in a way you described, however I see slightly different picture.

To me the fact that both standards co-existed for over 20 years only proves that ISO way of issuing different standards suffered from serious configuration management issues, at least in the past. In the first link you posted Figure 2 from ISO 8015:1985, but in the very same standard there is also Figure 3 showing what should be done to invoke envelope principle to the size callout. Then, as you said, ISO 286-1 came out in 1988 and from that moment I can't really understand how the default rule stated in it (and shown in your second link) could ever co-exist with the Figure 3 from ISO 8015:1985. It looks like at the moment of publishing 286-1 in 1988 nobody really cared about existing ISO 8015, so had no intentions to apply the default rule from 286-1 to 8015.

Besides, we are talking here only about size dimensions toleranced with ISO tolerance classes. Do you think it is enough to extend the entire concept to other size dimensions toleranced with different methods, like plus/minus, direct limits, etc.? In my opinion, it is definitely not.

 

[CheckerHater]

I really don't think that the picture you see is much different from what I see.

The argument was if envelope requirement could ever be overridden by straightness control under the ISO rules, and I think I was able to convince you that at some point this interpretation was possible.

I totally agree it was not intentional, merely configuration management issue, mis-communication of a sort between the sub-committees, no doubt about it.

Although I would be leaning towards the idea that if the override is possible in principle, symbology wouldn't really matter that much. BTW, is there a difference between plus/minus and direct limits as far as envelope symbol is concerned?

What interests me more, is "after 2010" situation. ISO is getting really heavy with fundamental standards trying to create some logical hierarchy. I am not very familiar with all of them, which makes me curious if some "conflicting requirements" or "direct vs. indirect control" rule allows for similar loopholes?

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[greenimi]

I am glad and very happy pmarc is back (time permitting). As far as CH, I know he is always here when we need help.
THANK YOU!!
I really, really, mean it!

 

[greenimi]

http://www.eng-tips.com/viewthread.cfm?qid=344229

Related or maybe not, to the above subject.
Hope it "confuse" even more!
Happy Valentine's Day!

 

[ak762]

What interests me more, is "after 2010" situation. ISO is getting really heavy with fundamental standards trying to create some logical hierarchy. I am not very familiar with all of them, which makes me curious if some "conflicting requirements" or "direct vs. indirect control" rule allows for similar loopholes?

I think in the same way.
CH, Could you reference at technical literature from where you extracted a sample with former practice of ISO 286. I did not find such clarification and always was confused with co-existed 286-1 and 8015 when I came in ISO world with GOST background

 

[CheckerHater]

@ ak762: ISO 286-1:2010 Annex A

Also ISO 8015:2011 is wa-a-ay different from ISO 8015:1985