Relax tolerance on all around profile 1

[greenimi]

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

 

[greenimi]

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

 

[CheckerHater]

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

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

 

[fsincox]

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

 

[fsincox]

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

 

[Belanger]

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

 

[pmarc]

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

 

[axym]

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.

http://www.axymetrix.ca

 

[CheckerHater]

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.

 

[fsincox]

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

 

[CheckerHater]

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?

 

[fsincox]

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

 

[CheckerHater]

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?

 

[fsincox]

CH,
Exactly!
Frank

 

[pmarc]

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).

 

[fsincox]

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

 

[CheckerHater]

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

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

How come one is wrong and one is right?

 

[pmarc]

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.

 

[CheckerHater]

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.

 

[pmarc]

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?

 

[pmarc]

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