In worst case, the flatness is... 7

[SeasonLee]

In worst case, the flatness on this surface is...
Please see the attached for details.
Thanks

Season

 

[greenimi]

Okay I understand.
I agree that for all practical purpose that flatness would be 0.6. Let’s get that out of the way.
Now from a theoretical point of view:

It is weird to disagree with such as authority (Tec-Ease experts), but I would say that the rule#1 is limited only to *a* section of the surface. What I mean?

The rule#1 is restricted/ applicable to regular feature of size, right?

Is the 30mm dimension regular feature of size, per Y14.5?

I would argue NO.

Because does not have a set of two opposed parallel surfaces. It has but not for its entire length. So it is regular for only a portion of its entire surface. So rule#1 would be applicable only for a limited surface. (the portion that has OPPOSING and PARALLEL surfaces)

So if the OP would ask what would the max flatness for the bottom surface I would agree that is 0.6. But for the top surface, since again, it is not subject to rule#1 (again because it is not regular feature of size) I would say it is not limited to 0.6.
Anyone see my point?
[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1441971579/tips/Straightness_Test_xwsvcz.pdf[/url]Have a great weekend everybody!

 

[dtmbiz]

3DDave,

Yup, blew that theory up
The error of my thinking was that the tolerance zones were oriented
parallel to the surface measured from. That was alot a grief for me
over simple orientation of the tolerance zones. I hope you just mentioned
that and it wasnt further up in thread. oiveh!
No wonder I have never used straightness of a line controls on a planar surface.
Cant think of why I would.
I really do like profile of surf and line much better.


greenimi,

The ole' ; is it a feature of size or not a feature of size?

Similarly this comes of with partial cylindrical features (not closed)
that do not have a full diameter.

A 100 mm cube has all edges with varying and mixed blends and chamfers
with a wide range of sizes (just to setup that no opposing surface is
exactly to the same extent).

Are there any features of size contained in the cube?


Maybe a new thread on features of size? and then again, maybe not

 

[Belanger]

Maybe a new thread on features of size? and then again, maybe not

Yes, that would be nice to see. I can't believe this question has played out as long as it has. (My 2 cents)

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

 

[greenimi]

Wouldn't be easier to answer my concerns/ issue here, in this thread, because there is related with the flatness.
If the rule#1 is not active or in effect, then the flatness wouldn't be controlled to 0.6, right? would be a different answer.

So, it is or is not ?
Just need your opinion.
No hard feelings, if I am wrong I am fine with it.

 

[CheckerHater]

From ASME Y14.5-2009:

1.3.32 Feature of size
feature of size: encompasses two types: regular and irregular. See paras. 1.3.32.1 and 1.3.32.2.
…
1.3.32.2 Irregular Feature of Size. irregular feature of size: the two types of irregular features of size are as follows:
(a) a directly toleranced feature or collection of features that may contain or be contained by actual mating envelope that is a sphere, cylinder, or pair of parallel planes
...

So, everything that fits between two parallel planes may be used as a feature of size. Have I answered your concern enough?

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

 

[greenimi]

So, if it is an irregular feature of size--as you stated above--, it is not subject to rule#1 !!

If it is not subject to rule#1 then the max flatness will not be controlled to 0.6 max, right?

Same standard as above (ASME- Y14.5-2009)

2.7 LIMITS OF SIZE
Unless otherwise specified, the limits of size of a feature
prescribe the extent within which variations of geometric
form, as well as size, are allowed. This control
applies solely to individual regular features of size as.......


2.7.1 Variations of Form (Rule #1: Envelope Principle)

The form of an individual regular feature of size is
controlled by its limits of size to the extent prescribed in
the following paragraphs and illustrated in Fig. 2-6.

 

[CheckerHater]

What's a big deal, your part still has "two opposed parallel elements", so it falls under "regular" as well.

I was just trying to show how far today's definition of FOS was stretched.

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

 

[greenimi]

I would say has two opposed parallel elements but only for a portion of the surfaces we are talking about (the flatness in question is for the entire surface), so the rule# 1 is only for a portion / area of the surface in question and not for its entire length/ width.


Do you see my point?

 

[CheckerHater]

No, I don't.

If envelope principle applies, envelope encompasses the entire feature, not the part of it

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

 

[greenimi]

Quote: "If envelope principle applies, envelope encompasses the entire feature, not the part of it "

My question: Where does it say that?


Probably you will answer:" where does it say that does not encompasses the entire feature?"

And my answer would be in "two opposed parallel elements"

Not the entire feature has OPPOSED and parallel elements.

 

[Belanger]

CH -- I think greenimi is asking this; see my graphic: Would you say that the flatness of the entire bottom surface is limited to 1 mm (based on the height tol) because the "envelope" goes across top and bottom?

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

 

[greenimi]

Let’s say/assume that the step in the J-P Belanger example is dimensioned to 7 ± 0.4 mm.

The question is what would be the maximum flatness allowed for the bottom surface?
1mm? 0.8mm? other combination?

 

[CheckerHater]

Belanger and greenimi,

Allow me to counter your questions with very simple yes-or-no question:

By your own logic, does Rule 1 apply to the part on the picture?

Yes or no please.

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

 

[greenimi]

Yes.

 

[CheckerHater]

How about this part?

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

 

[Belanger]

CH: Nice try that is virtually same question I asked (you just changed the picture, essentially), so I'll be interested in your answer.

I will offer this: Our current discussion seems to revolve around a very specific detail within Rule #1: Paragraph 2.7.1 clearly states that it applies to a regular FOS (and thus not to an irregular FOS).

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

 

[CheckerHater]

Nice try J-P,

So, yes or no?

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

 

[Belanger]

See my post from 15:51 today. Wouldn't you say that my Q came first? So I'll await your answer on my graphic.


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

 

[Belanger]

Well, I'll rise above the fray to tip my hand. I think the ASME standard really needs to clarify the definition of a regular FOS to say "directly opposed elements" rather than "opposed elements."
Anyhow, a purist would say that on my picture the bottom surface's flatness is 1 mm -- only for that small area that stays directly below the top ledge. (The remainder of the surface would be held flat within the tolerance on the height of the longer shelf, which isn't currently shown over on the right side.)
Similarly, it could be said that on your picture, CH, the bottom surface's flatness is held to within the size tolerance of the main part, except for the imaginary circle that sits under the hole's location, since that area isn't a regular FOS derived from the main part's size.
Having said that, I don't know anyone who would really cling to such a nitpicky view. We'd all probably agree with greenimi and say "yes" to your question. But we've exposed a need for clarification in Y14.5.

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

 

[greenimi]

J-P Belanger,
Amen. Thank you for reinforcing my point.
Also I would say that for the first picture CH posted - the one with a hole- for all practical purposes my answer is still yes. But for the second picture CH posted for the same practical purposes I would vote for No.
I agree that the standard would be better if the proposed definition is clarified with that addition or similar one.
Where we draw the line between first CH picture and the second one - again in the real world - I don't know.
Maybe we also have to think how the features ACT in assembly not only if they have direct opposing elements or not. Just a thought.