free state 1

[cervantes]

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

 

[pmarc]

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?

 

[CheckerHater]

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

 

[CheckerHater]

@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

 

[pmarc]

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?

 

[CheckerHater]

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?

 

[Belanger]

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

 

[CheckerHater]

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

 

[Belanger]

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

 

[powerhound]

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

 

[pylfrm]

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

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.

 

[CheckerHater]

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?

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

 

[greenimi]

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.
Have a great weekend everyone

 

[pylfrm]

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

 

[3DDave]

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.

 

[CheckerHater]

@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

 

[Belanger]

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

 

[pylfrm]

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.

... 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