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free state

free state

free state

(OP)
Hi

there is only one example in ASME standard and it is also hard to find anything else in the net.

There is a small plate of aluminium 3x15 which bends under its own weight or it is just naturally bended due to material physics.

It will be attached later to flat surface so it will be straight anyway.

But to clarify the drawings and reduce number of quality reports - can I use free state for straightness like presented on the drawing?

I meant - in free state, straightness of profile can be between 5 mm's.

Any other tips? Is this one is ok?

Thanks

RE: free state

Yes, using Free state modifier implies that your part is flexible and special considerations are required.

You may also specify tolerances in restrained state and HOW exactly you want part to be restrained for inspection. (Usually simulating assembly)

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

RE: free state

(OP)
thanks, but do you have any objections with regards to my rough drawing proposal?

RE: free state

The drawing really is "rough", so it's hard to tell.

The (F) symbol should be next to tolerance value and not in its own compartment.

Also, depending on what are you actually measure, you may want to specify flatness rather than straightness.

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

RE: free state

But recall that Rule #1 automatically goes away for a non-rigid part. So one could argue that the F modifier isn't necessary here.

I've only used F when a part is restrained per a general note yet I want one particular feature control frame to be checked in the unrestrained condition.

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

RE: free state

(OP)
thanks all

Belanger: I am an European, we do not have envelope requirement as a default option

RE: free state

Quote (Belanger)

But recall that Rule #1 automatically goes away for a non-rigid part. So one could argue that the F modifier isn't necessary here.

But how do you know that part is actually flexible?

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

RE: free state

Cervantes -- sorry I hadn't realized that the discussion pertained to ISO.

CH -- (back to ASME for a moment) -- is it true then that a non-rigid part must either have the free-state modifier or else have a restraining note?

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

RE: free state

J-P,
Re:" is it true then that a non-rigid part must either have the free-state modifier or else have a restraining note?"

What about having only AVG note near the size dimension? Does it make it flexible?

RE: free state

Green, that's not my concern right now ... let me wait on that one. The question is whether Y14.5 requires tolerances for a non-rigid part to be given the F modifier, or tagged with a restraint note, or neither is required?

Not a trick question -- I'm honestly asking how folks interpret para. 2.7.2(b) and 5.5-5.5.2.

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

RE: free state

Thanks (really) but I disagree: Frames with and without F actually do have the same meaning.
Paragraph 4.20 clearly states that "all tolerances apply in a free-state condition." So the F symbol is not needed, even on flexible parts! The only reason F would make sense is to provide a specific FCF with an escape clause from a general restraint note (see para. 5.5.1).
I think that's the point of Meadows' example.

But what I'm saying is that his first picture didn't need to have the F. If the first Meadows example had no F, we'd interpret it the exact same way according to Y14.5. So is there some magic symbol to connote that a part is non-rigid? No.

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

RE: free state

F combined with FCF overrides the rule that form tolerance must be refinement of size dimension. So different meaning indeed.

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

RE: free state

Quote:

F combined with FCF overrides the rule that form tolerance must be refinement of size dimension.
No it doesn't. That would be the I modifier.
F just means the FCF shall be checked in the free state. But this all illustrates an inconsistency in the standard. Yes, Fig. 5-13 uses the "F" but that's not needed if you really read para. 4.20.

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

RE: free state

Just read the book:

From ASME Y14.5-2009:

Para. 5.4.3: “The circularity tolerance must be less than the size tolerance…”
Para. 5.5.3: “Note that the free-state circularity tolerance is greater than the size tolerance on the diameter” (Fig. 5-13)

Look at the accompanying illustrations: circularity tolerance without F are less than the size tolerance, circularity tolerance with F are greater than the size tolerance.

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

RE: free state

I believe you are familiar with the "I" -- what does that mean in regards to the relationship between size and form?

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

RE: free state

Sorry, I don't follow. Are you trying to steer the discussion in different direction?

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

RE: free state

No, I was challenging your statement that F nullifies Rule #1. Agree that that's the job for I?

I guess I'll repeat my point: This all shows that there are paragraphs in the standard you can lay side by side, and there will be inconsistencies (or at least ambiguities).

A) Free state is the default.
B) Size tolerances control form (in ASME).
C) Free state modifier signifies a free-state check.

Clearly, statement C isn't necessary because of statement A. (The exception there is if a general restraint note.)
You're saying that statement C nullifies statement B. I guess I get that only because F seems to be otherwise useless in Fig. 5-13.

But can we agree that something is weird about all this? Maybe they need to re-write paragraph 4.20.



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

RE: free state

I apologize that this will be really short entry, but due to tight schedule I am not able to offer more at the moment.

Question to CH:
You said (quoted) that the circularity tolerance must be less than the size tolerance. And I agree, in Y14.5 realm this is absolutely true for parts not subject to free state variation or parts subject to free state variation in restrained state. But assuming for a moment that on the Fig. 5-13 there is no F modifier in the circularity feature control frame, what would the size tolerance for the diameter specified on that drawing be?

RE: free state

I really don't think F means the FCF shall be checked in the free state. That's what Para. 1.4(m) is for.

F means that feature is subject to variation in free state. There is a slight difference.

Just like between "Perfect form at MMC not required" per Para. 2.7.3 ((I) symbol), and "Form control does not apply" per Para. 2.7.2(b).
Both override Rule 1 but for different reasons.

(I) means you don't want Rule 1 to be applied, (F) means you can't apply Rule 1 (Para. 2.7.2(b) refers to Para. 5.5 and Para 5.5 refers to (F) symbol)

And I totally agree that one can write a book on inconsistencies of Y14.5

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

RE: free state

@pmarc:

I have no idea. In my opinion, that would be illegal to have roundness larger than size tolerance. What the actual size tolerance would be is a bogus question.

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

RE: free state

Okay, let me put it this way. On Fig. 5-13 (with no F modifier) roundness tolerance is 10. Why are you saying it is larger than the size tolerance?

RE: free state

Because it is larger than size tolerance? Because "average" diameter is meaningless by itself? Because I need just a hint if Roundness of 10 is "functional" requirement or something else?


RE: free state

CH: I think pmarc is saying that the AVG thing isn't a size tolerance at all (it is, but only for the imaginary average, not the real size).

So we're back to... why use F at all? Methinks it was kind of like the ST modifier. "Gosh, we need some symbol for this (or that)" but then they didn't flesh it out very well. Which is why it leads me to think that its only use is to override a general restraint note.

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

RE: free state

AVG is not imaginary.

It's the size of your GO/NOGO gage. It is very real and it is functional requirement.

Let's go back to OP. You have part that has two flatness requirements. To me F removes the ambiguity. Do you have better idea?

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

RE: free state

For your last question, CH, see para. 4.20. There was never any ambiguity to begin with.

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

RE: free state

Sounds like this is mostly wrapped up but I guess I'll chime in anyway. I've always understood the F to mean that a feature was to be inspected in the free state. This only makes sense when there is a restraint note stating that other features are to be inspected under some form of restraint since 1.4(m) states that the default condition for inspection is in the free state. I think the example of AVG on an o-ring type part using the free state modifier is not the same thing as cervantes is asking about but I agree that it adds to the confusion since it seems to suggest that the free state modifier overrides rule #1 (which it doesn't). It's the fact that it is a non-rigid part that makes rule #1 non-applicable here.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II

RE: free state

How do you determine whether a part or feature is "subject to free-state variation"?

Quote (ASME Y14.5-2009 para. 5.5)

Free-state variation is the distortion of a part after removal of forces applied during manufacture.

It seems to me that all parts are subject to this to some degree, so where do you draw the line? Furthermore, this definition seems to go against the general principle of separation between the drawing and manufacturing methods.

RE: free state

Quote (Belanger)

For your last question, CH, see para. 4.20

If you have noticed, I was trying to provide an actual quote and my interpretation of it. Could you return the courtesy?

Quote (pylfrm)

It seems to me that all parts are subject to this to some degree, so where do you draw the line?

It's very simple. It depends on the tolerance and the tool you are using to measure it. If you cannot measure it, it doesn't exist.

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

RE: free state

I would say that using the abbreviation AVG ( in the Buna O-ring case) make it the feature to be an exception from rule 1 and not because F symbol is used.

The free state symbol may be placed to clarify a free state requirement on a drawing containing restraining feature notes. If no restraing notes, then no F symbol.
Also, F symbol may be placed in order to separate a free state requirement from associated feature which already have the restrained requirements. Again, in my opinion, no restrained requirements then no F symbol.

Ch,
Please bring back the traffic sign versus GD&T picture.banghead
Have a great weekend everyone

RE: free state

CheckerHater,

That interpretation doesn't sit very well with me.

As an example, imagine you clamp an incomplete part in a vise and machine away a bit of material, completing the part and creating a feature of size in the process. Everything is within tolerance, including envelope principle. You remove the clamp force, and the part is now distorted due to the internal stresses released by material removal. The feature of size now violates the envelope of perfect form at MMC by ten times the tolerance. The geometry and material are such that the part is still very stiff. Do you get a pass on the envelope principle because the part was subject to free-state variation? Is the customer going by happy when they inspect it? For all they know, you bought stress-relieved material and just machined it curvy.

I would think the designer needs to know if the envelope principle applies before the first part is made, and the inspector needs to know without knowing any details of the manufacturing process. Am I missing something?

- pylfrm

RE: free state

CH,

That picture from Meadow's book is one of the not so good examples. in the first illustration is a situation that doesn't need the (F) modifier because that's exactly how the part is supposed to be evaluated. In the second illustration, what on earth can applying torque to random clamps have to do with restraining force? Just put the pressure or force directly on the drawing and be done with it.

RE: free state

@pylfrm:

This is what I was saying: if you can measure the effect of variation in free state, then you have to take it into consideration. If you cannot measure it, how do you even know it's there?

@greenimi:

Here you are.

I am out of this. Not convinced, just old and tired.

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

RE: free state

Quote (CheckerHater)

If you have noticed, I was trying to provide an actual quote and my interpretation of it. Could you return the courtesy?
Sorry. I figured if you've been quoting from the book throughout this thread that I wouldn't need to retype a paragraph that's in the same book. But here...

Paragraph 4.20: Unless otherwise specified, all tolerances apply in a free-state condition. In some cases, it may be desirable to restrain a part on its datum features to simulate their function or interaction with other features or parts. To invoke a restrained condition, a note is specified or referenced on the drawing defining the specific requirements.

My interpretation: Unless otherwise specified, all tolerances apply in a free-state condition. The rest of it goes on to explain the exception, which is restrained parts.
My interpretation continued: If everything except restrained parts are to be checked in free state (as deemed by the paragraph I've cited), then it's reasonable to claim that the only purpose of the "F" is to have certain FCFs be exempted from a general restraint note.

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

RE: free state

So does free state variation refer only to geometry changes that take place well after removal of forces applied during manufacture? I had been interpreting it to include distortion that actually takes place during removal of forces applied during manufacture, but is permanently and consistently present afterwards (as I attempted to describe in my example). Perhaps this is the distinction you're getting at ChecketHater.


Quote (Belanger)

... the only purpose of the "F" is to have certain FCFs be exempted from a general restraint note.

This has been my interpretation as well, except I'd say it can be applied to any tolerance (not just those in FCFs) or datum feature reference.

- pylfrm

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