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Relax tolerance on all around profile

Relax tolerance on all around profile

Relax tolerance on all around profile

(OP)
A pentagon shape is controlled by .005 al around profile (no datum). The mating part is a similar shape part. The product engineer is insisting to add another callout to lessen the tolerance on two sides of the pentagon. In other words, from 5 sides, three of them to be in .005 and the other two in .010 AND still use all around profile. How can I legally, do that?


I realize that I’m speaking somewhat theoretically, but I would like to know what options/tools Y14.5 can offers.


I was thinking to use in between profile (name the corners A, B, C, D and E and use profile between A and B, and another
profile between B and C, etc), but in this case can I use all around profile (for assemble-ability with the mating part)?


Thank you

RE: Relax tolerance on all around profile

Make [.300] toleranced dimension.

RE: Relax tolerance on all around profile

(OP)
And if I am doing that (.300 toleranced dimension) woundn't be in conflict with .005 (ALL AROUND)?
My point is: doesn't all around profile require that all the dimensions to be basic?

RE: Relax tolerance on all around profile

There is HUGE discussion about using both datums and basic dimensions with profile.
I personally believe that you can use anything that works, especially if your profile is actually straight line.
For more insight on varying level of control using profile you can take a look at this newsletter:
http://www.mechsigma.com/newsletters/2005_07_Newsl...
Disclaimer: I don’t work there.

RE: Relax tolerance on all around profile

The idea with profile BETWEEN concept looks fine to me - however without profile ALL AROUND then.

But that brings up another question:
Can we treat datumless profile requirements defined for each segment using BETWEEN concept as simultaneous requirement then? With ALL AROUND we could for sure. With BETWEEN - I am not so sure, and that is why I would recommend placing SIM REQT notation under each profile FCF to avoid confusion.

Of course, the problem exist only if we assume that profile callouts with no datum feature references are applied (this may be a case when whole contour is used as primary datum feature). If, however, the contour is oriented/located relative to any datum(s) and the BETWEEN profile callouts reference to this datum(s), simultaneous requirement will be there.

As for .300 dimension being directly toleranced (and not related to any datums):
If other sides of the pentagon are controlled by profile tolerances with no datum feature references, any angular relationship between .300 width and the other sides of the pentagon will not be controlled at all. Keep in mind that directly toleranced dimension is not verified relative to anything. In other words the .300 width inclined at let's say 45 degrees to upper face of the pentagon will meet the print without any problems.

RE: Relax tolerance on all around profile

If it is not "all around", then, why say it is? Two profile callouts will do it, too.
Frank

RE: Relax tolerance on all around profile

Hi All,

Pmarc brings up some subtle but significant issues, and I agree with everything he said. The different "datumless profile" FCF's will not have simultaneous requirements by default. The features grouped by each between symbol will be simultaneous with each other, but there will not be a simultaneous requrement between the groups unless the SIM REQT annotion is used.

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Relax tolerance on all around profile

Just to make it clear: when I suggested making .300 toleranced dimension, I meant to keep all-around profile requirement.

RE: Relax tolerance on all around profile

(OP)
Is it legal to combine ± toleranced dimension with ALL AROUND profile?
CH,
The newsletter you indicated, shows combining ± toleranced dimensions with profile, but not with all around profile.

RE: Relax tolerance on all around profile

I really don’t see the difference.
In the newsletter profile is applied to smooth curve.
In your example all-around symbol allows your profile definition to “go around the corner”. Imagine that your example didn’t have all-around symbol, but had rounded corners. The symbology just clarifies where to stop (or not to stop).
What’s important is the idea that tolerance zone is allowed to “float”, so your dim tolerance adds to the value of profile.
Ask yourself: what makes you more uncomfortable – the ideas in the newsletter, or demand of your product engineer? After all it is definitely legal to drop all-around requirement and tolerance the part completely different way.

RE: Relax tolerance on all around profile

I think it will not be a surprise if I say that I see more disandvantages than advantages of having .300 directly toleranced and profile all around at the same time.

Not to mention that geometrically this will never be equivalent to having .300 width basic and two looser profile of surface tolerances applied to both surfaces of the width.

RE: Relax tolerance on all around profile

I am not defending my idea as the “best solution”.
The way I understood it, OP was not about finding simple “textbook” solution, but rather some weird way to make profile tolerance .005 and .010 at the same time to satisfy other engineers requirement.
I came up with weird suggestion (which I think still has some merit).
We can try to discuss it further or simply say “No, one cannot have profile tolerance .005 all-around and also .010 in some places all at the same time”.

RE: Relax tolerance on all around profile

Ch,
Thank you for posting that sheet, very interesting.
Frank

RE: Relax tolerance on all around profile

I have 2 questions regarding the newsletter attached by CH:
1. Which paragraph/figure of Y14.5M-1994 standard (I assume it is '94 edition, since the newsletter is from 2005) says that directly toleranced dimensions have power to locate geometrical tolerance zones as suggested by the text associated with figure 2?
2. Which paragraph/figure of Y14.5M-1994 states that presented way of attaching profile FCF with part's outline (all figures) applies to whole contour of the part?

RE: Relax tolerance on all around profile

Pmarc, I agree with you on one of those points. But first, what is your issue with Figure 2's text? I don't see anything wrong with their Figure 2 as far as the "directly toleranced dimensions" goes. They are saying that those D.T.D.s only orient the zone, but not locate it. That sounds right to me.

I agree with your second point: a purist would say that the profile tolerance in all those figures only applies to the straight portion (the upper segment of the hourglass shape). As soon as we hit the radius, it's technically a different "feature." However, many would say that the basic dimensions for the radii leave us no choice but to think that the profile continues for the entire hourglass.

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

RE: Relax tolerance on all around profile

"Since we used a "plus/minus" dimension (7.24±.05) to locate the profiled surface to datum A, the profile tolerance does not control location."

RE: Relax tolerance on all around profile

The profiled surface is being located. The profile tolerance is not being located.
(In other words, the tolerance zone goes to wherever the surface happens to be.)

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

RE: Relax tolerance on all around profile

That is even worse, unless you see nothing wrong in applying directly toleranced dimension to the center of radius.

RE: Relax tolerance on all around profile

ASME Y14.5-1994 has absolutely no problem with using directly toleranced dimensions to specify profile.
From Para.6.5: “If the drawing specifies individual tolerances for the elements or points of a profile, these elements or points must be individually verified.”
If you have tolerance, you check it – that’s the only concern.
And later: “the true profile may be defined by basic radii…dimensions…, etc., etc., etc.
No “must”, no “shall”, not even “should”.

RE: Relax tolerance on all around profile

So you guys are OK with profile specified as stated? Back when I mentioned doing something like this to replace runout it seemed to cause a stir?
CH,
Who is this expert anyway, I notice no name is mentioned?
Frank

RE: Relax tolerance on all around profile

(OP)
Frank,
http://www.mechsigma.com/ go to Qualifications

--------------------------------------------------------------------------------
Paul Drake and Dale Van Wyk founded MechSigma Consulting with a mission of designing mechanical products that meet quality goals without compromising manufacturability or performance.

Our expertise includes 35 combined years of experience as mechanical design engineers and 20 combined years of experience in mechanical design for Six Sigma. We have successfully deployed Six Sigma mechanical processes at Raytheon Systems Company (formerly Texas Instruments Defense Systems and Hughes Missile Systems) where we co-managed the Mechanical Tolerancing and Performance Sigma Center for Excellence.
Our qualifications include:
Degrees / Certifications
Paul Drake
BME, BA/Physics
ASME Certified Senior Level Geometric Dimensioning and Tolerancing Professional
Registered Professional Engineer (Texas)
Six Sigma Blackbelt



ALSO

From Y14.5-2009 page Viii
SUBCOMMITTEE 5 — DIMENSIONING AND TOLERANCING
among others....
P. J. Drake, Jr., MechSigma Consulting, Inc

RE: Relax tolerance on all around profile

Don't forget "Membership on ASME Y14.5.2 Certification of GD&T Professionals subcommittee"

They don't just pass exams, they design them. smile

RE: Relax tolerance on all around profile

Sorry, if I offended,
I understand the information was provided for to me for free and so is at least as good as what I paid for it, I just want to know,before I consider it seriously, how this opinion stands up relative to the other "experts" here. I myself have liked to take a more "liberal" interperetation of the standard and I see this as in that vein.
Thank you, greemni

RE: Relax tolerance on all around profile

greenimi,
I have acquired a certain level of respect for say the opinions of some members here, I am just trying to better understand the background because this is more in line with a line I might take.
I am nobody.
So if I am going to really accept the information I really want to vet it first. The credentials you state are impressive and lend a certain weight to the point. Being a member of the committee is more like knowing the inside story. I was trained by one and learned the politics of it, I know it is not always so cut and dry.
Frank

RE: Relax tolerance on all around profile

pmarc -- I didn't look too closely at the details of their dimensioning scheme; I just meant that there's no conflict in saying that a profiled surface does one thing, whereas a profile tolerance zone may do something different.

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

RE: Relax tolerance on all around profile

I understand, J-P.
I am looking at the details in this case and I am not comfortable with the scheme.

RE: Relax tolerance on all around profile

Hi All,

For what it's worth, I'm not comfortable with the scheme either (even though one could argue that the standard allows it). Y14.5 allows the mixing of directly toleranced dimensions with Profile to a degree that I'm not comfortable with.

As pmarc has mentioned, there are disadvantages to mixing directly toleranced dimensions with basic dimensions in a Profile tolerance specification. The main disadvantage for me is that it's non-rigorous - just a couple of examples in the standard (possibly only one) and no rules. Figure 8-27 in Y14.5-2009 shows Profile of a Line in combination with a directly toleranced dimension. The text mentions that in this application, the datum references only orient the Profile of a Line tolerance because size is controlled by a separate tolerance. But that's it - no other explanation is given. So we are left to wonder how directly toleranced dimensions would affect Profile tolerances in other cases such as the one in the newsletter.

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Relax tolerance on all around profile

I find it really difficult to understand everybody’s concern.
Profile requires two things: true profile and tolerance value.
True profile must be defined by basic dimensions (maybe). OK with me.
Nowhere in the standard has it said profile should always apply to the entire part.
So, the “true profile” may be connected / attached to the rest of the part by different means: toleranced dimensions, basic dimensions, with or without a datum.
Every different way of incorporating profile into the drawing has a different meaning.
Please take a look at the enclosed picture and tell me what is wrong with it.

RE: Relax tolerance on all around profile

CH,
While I support the "expanded" use of profile, I believe the uneasiness comes primarily from a general basic distrust of all "toleranced dimensions" (except primarily for features of size) as also expressed in the 2009 foreword of the standard about the third paragraph down. While those of us, who work in industry, have to struggle to rectify this "idealistic concept" with what we live with day to day.
Frank

RE: Relax tolerance on all around profile

Frank,
Did you notice that all toleranced dimensions on my example are measurable envelope dimensions that qualify as at least “irregular” features of size?
What (or whom) we really distrust here?

RE: Relax tolerance on all around profile

CH,
I was referencing your earlier example not your latest example, your new example is much closer to the textbook case. I really don't trust, myself, what to do with dimensions like in the earlier post anymore. I would tent to want to use composite profile to do the things in the earlier example. However, if I saw it on a drawing I would try and work with it and, like you, not call it wrong/illegal.
Frank

RE: Relax tolerance on all around profile

Thank you Frank,
As you noticed I called my own suggestion “weird”. I thought that was the challenge.
All around means all around. The only way I see to “loosen” all around requirement in some places is to allow tolerance zone itself to float in said places (and we still have legal ways to do it, for better or for worse).
Personally I would try to convince “the other engineer” to drop all around requirement and specify what we need where we need it.
Could I be any more clear?

RE: Relax tolerance on all around profile

CH,
Exactly!
Frank

RE: Relax tolerance on all around profile

This is what I am not comfortable with when I look at figure 2 and associated text in the newsletter:

1. At the top of page 2 the newsletter says: "Since we used a "plus/minus" dimension (7.24±.05) to locate the profiled surface to datum A, the profile tolerance does not control location." This underlined statement is not in accordance with Y14.5M-1994. By default, directly toleranced dimensions are not associated with any datums, unless explicitly stated (see note at the end of paragraph 4.4), so at the fundamental level they can't be used to locate features relative to datum(s). If 7.24±.05 dimension controls anything, it is unclear, unrelated, not standardized distance between virtual center of 3.40 arc and datum feature A.

2. If 7.24±.05 dimension has center of 3.40 arc at one end (and is not locating profile tolerance zone like J-P suggested), good luck with finding this center in a repeatable way. Not to mention that by applying directly toleranced dimension to the center of the arc one loses the biggest advantage of profile of surface tolerance, that is no need to find any virtual centers of arcs that the toleranced contour comprises.

As Frank mentioned, composite profile FCF (with reference to A in both segments plus basic 7.24) would easily and unambiguously solve the issue once and for all.

And I hope this discussion (about the newsletter) reveals at least partially the reason why the statement made in the foreword of Y14.5-2009 appeared in the standard: "This revision contains paragraph that give a stronger admonition than in the past that the fully dimensioned drawing should be dimensioned using GD&T with limit dimensioning reserved primarly for the size dimensions for features of size".

Is it "idealistic concept", as Frank named it? Perhaps, but this is what GD&T is all about - to define part's geometry fully and as clearly as possible. It is a shame that in the same time the very same standard shows figures that contradict cited part of the foreword (fig. 2-4, 3-29, 8-7 to name just a few).

RE: Relax tolerance on all around profile

pmarc,
Sorry, I guess I should have said: "all my people who are sure they know better, how to measure a part like the first example when a non-basic dimensions are used have the idealistic concept".
Frank

RE: Relax tolerance on all around profile

Quote (Newsletter)

Since we used a "plus/minus" dimension (7.24±.05)..., the profile tolerance does not control location

Quote (pmarc)

By default, directly toleranced dimensions... can't be used to locate features

How come one is wrong and one is right?

RE: Relax tolerance on all around profile

CH,
Why have you removed the underlined portion of the text from the first quote? The answer is exactly in this removed part. According to the newsletter they "used a "plus/minus" dimension (7.24±.05) to locate the profiled surface to datum A". This is simply a violation of Y14.5M-1994. By default directly toleranced dimensions do not locate to datums. They merely control a distance between features.

RE: Relax tolerance on all around profile

I’ve read thru Para 4.4 and following note; it’s about order of precedence.
I’ve read thru Newsletter; they do not attempt to “locate” anything until Figure 3.
I am not going into discussion of “location” vs. “position” vs. “distance” vs. whatever again. There is no definition of “location” in the standard.
We better stop this argument before it started.

RE: Relax tolerance on all around profile

Para. 4-4 about order of precedence? It looks like you missed the part of the note: "When necessary to relate linear and angular dimensions to a datum reference frame".

But should this surprise me, especially when you are saying that despite of "Since we used a "plus/minus" dimension (7.24±.05) to locate the profiled surface to datum A", they do not attempt to locate anything until Figure 3?

RE: Relax tolerance on all around profile

It should have been: "The note in para. 4.4 about order of precedence?"

RE: Relax tolerance on all around profile

Hi All,

The discussion about the meaning of "locate" illustrates some of the potential problems with this kind of spec. There are no rules for the application of directly toleranced dimensions to anything other than features of size. So we are left to figure them out for ourselves, which can result in different opinions. The following question could be asked:

What does the center point represent on a real part? Is it the center of an arc derived from the as-produced surface, or is it part of the definition of the Profile tolerance zone? I believe that this could be argued either way.

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Relax tolerance on all around profile

Evan,
Regardless of whether you agree with the commments I made about figure 2 from the newsletter, I thank you for your last reply.
Why to use a dimensioning technique for which there are no rules in the standard? Especially that there are methods to accomplish similar effect without any ambiguity.

I wish future editions of Y14.5 put slightly more emphasis on showing why certain dimensioning and tolerancing methods are bad from geometric definition point of view. Yes, I realize there is no way to gather all crazy ideas in one handy document, but some of the most frequent errors could be presented. Perhaps then we would not have debates like this one.

ISO did it in one of their standards - ISO 14405-2:2011 "Dimensions other than linear sizes". The one attached below shows ambiguity of directly toleranced dimension applied to stepped non-opposite surface (but the example of directly toleranced dimension applied "between" surface and virtual center of hole is also there).
http://files.engineering.com/getfile.aspx?folder=a...

It would be quite informative for Y14.5 users to see something like this, don't you think?

Oh, and it would also force the committee to improve figures 2-4, 3-29, 8-7 from '09 edition smile

RE: Relax tolerance on all around profile

I believe this is the same thing I was getting at. First you have to get the committee to make it clear the old way is not suitable and then you have to convince thousands of buisnesses that it makes a difference to them. It seems kind of like convincing people thay should invest in health insurance, when things are going good they don't want to listen, when things go wrong then they wish they had.
Frank

RE: Relax tolerance on all around profile

(OP)
Pmarc,

Just to blend a little my response with Frank’s, I would say that we are now in an intermediate phase of the profile “definition”.

1994: Fig 6-18 concept has not been included into 2009 (transition phase). I don’t know why, maybe because was never valid a truly design / possible real design requirement. This (transition phase) is the equivalent of “mandatory health insurance”, but if you don’t have it (insurance), you pay a small fine.

Now, maybe in 2012 or 2024, Y14.5 standard will no longer allow mixing of directly toleranced dimensions with profile, so Fig 8.27 / 2009 will be no longer carried over in 2021/2024 Y14.5 standard and accordingly the principle supported by the standard with Fig. 8.27 will go away. (why I said 2021 because 1994 - 1982= 12 + 2009 = 2021) along with improvements for the picture you mentioned (2-4, 3-29, 8-7). And to "help" Evan maybe 8-18 will get a revision too.
(and BTW the health insurance premium will be directly seen as direct deduction from the payroll same as the social security is now with no longer option to pay a fine and go without)

RE: Relax tolerance on all around profile

greenimi,
I have no objections to mixing profile with directly toleranced dimensions in general. I just raise a red flag when it is done in a way that creates ambiguity.

There are quite few cases (per my experience) when mixing profile with directly toleranced dimensions does not lead to ambiguity, but there are such. Fig. 8-27 in Y14.5-2009 is one of them (although the very same requirement could be expressed through parallelism FCF with additional notation EACH ELEMENT below the FCF). But as we know, GD&T is a language, so the same thing can be said using different words/symbols. And I see nothing wrong with that as long as these different words/symbols are not in conflict with general rules of the language.

RE: Relax tolerance on all around profile

pmarc,
Thank you for the link, I have added it to my arsenal to show it around here.
Frank

RE: Relax tolerance on all around profile

You're welcome, Frank. Show it - in my opinion this picture is worth more than thousand words.

RE: Relax tolerance on all around profile

It helps with Engineers, who do not understand all of this, if it has the "national standards" stamp and it gives it a "well this is what we have been missing" kind of feel.
P.S. You know how I like information on ISO standards :)
Frank

RE: Relax tolerance on all around profile

I would say the content of ISO 14405-2:2011 is quite revolutionary. Y14.5 is not that far yet, but hopefully it will in 2021 or 2024.
It is really worth to have it on the shelf.

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