Correct or not? And how to inspect?

[gabimo]

Are the parallelism calouts correct in Y14.5? Also how to inspect these orientation callouts at MMC?

Thank you
Gabi

 

[CheckerHater]

No, they are not correct.

Parallelism as surface control is not using L or M modifiers.

To control parallelism of derived middle plane,
a) controls must be attached to appropriate FOS dimensions.
b) FOS must look like FOS (it may be argued if 1.000 dimension represents FOS of not).

So, better job could be done to control parallelism of these particular features.

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

 

[greenimi]

So, if they are using DMP flatness-DMPF- (as they should) how the DMPF will control the surface parallelism?

I know that flatness will control DMPF, but what about the parallelism? How to relate DMPF with the required parallelism?

My assessment:

You derive the median plane from the surface, there is no way that the DMP flatness could ever be greater than the surface flatness.

* flatness controls DMP (derived median plane) flatness, but DMP flatness does not control surface flatness. As long as the out-of-flatness of the surface is symmetrical, the DMP stays flat.

* specifying DMP flatness, the value in the feature control frame can be less than, equal to, or greater than the total size tolerance -- whatever is functional.

My follow up questions are above.

 

[CheckerHater]

@greenimi:
I think you are comparing apples to oranges here.

Flatness cannot control parallelism. There is no relation.

Maybe you could chose different wording for your question, or, better yet, provide a little sketch.

Right now it's a bit confusing.

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

 

[greenimi]

Okay. So let me do it over. The original design intent was to control the parallelism. You recommended to use DMPF? (align the flatness callout to the size dimension or you wanted to align only the parallelism callout with the size dimension).
If not, I will stand corrected.

Please advise and sorry for the confusion.

 

[CheckerHater]

I did not recommend anything. I just noted that GD&T was confusing to say the least. There was no word "flatness" in my post.

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

 

[greenimi]

Okay. Fair enough.

Just for academic purpose only and additional challenge (since the OP question has been answered)

So, how would you change the parallelism requirement to DMPF and get the same mathematical scheme (as the parallelism) ? I understand that the flatness could not control parallelism, but since the surface it is a regular FOS probably “some adjustments” can be made to make these callouts equivalent.
There is such or equivalency?

 

[CheckerHater]

Based on this very old picture,

http://files.engineering.com/downlo...bf33-484c-ac71-fd99ff92ad94&file=FLATNESS.bmp

And providing that Rule 1 is in action, you could shrink size tolerance until both flatness and parallelism satisfy your demand.

Unless you are trying to ask something else?

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

 

[powerhound]

I'm reading about a derived middle plane in this thread. I'm assuming it's the same as derived center plane. If so, how did that even enter the conversation? I see no reference to a derived center plane on this part at all. I do agree that the parallelism callout is wrong for reasons the CH stated but how it went from that to a derived center plane is a mystery to me.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

 

[greenimi]

John,
Just for academic purpose only and additional challenge (since the OP question has been answered)

 

[powerhound]

Ah. Okay.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

 

[pmarc]

John,
What is 'Derived Center Plane'?

 

[powerhound]

 

[Tunalover]

What does "DMPF" acronym mean?

Tunalover

 

[greenimi]

DMPF = derived median plane flatness (for this thread only)---to avoid typing over and over the same 4 words.

 

[gabimo]

“To control parallelism of derived middle plane,
a) controls must be attached to appropriate FOS dimensions.”

May I ask you: What is the difference between: “parallelism of derived middle plane” and “derived median plane flatness”

Will DMPF control parallelism in the case shown?

Thank you
Gabi

 

[CheckerHater]

Try to visualize something that is flat, but not parallel to anything.

And no,flatness will not control parallelism.

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

 

[greenimi]

Ch,

My questions for you would be:

What about DMPF in combo with the size dimension for regular features of size, will that indirect control the parallelism?

 

[CheckerHater]

Once again, no

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

 

[greenimi]

CH and everybody,

It is hard for me to believe that DMPF combined with the size dimension would have no effect over the maximum parallelism allowed for the feature of size.

In other words, lets say along with the size dimension a DMPF callout is added such as DMPF in .010 at MMC. The question (could be a GDTP exam question? ): what would be maximum parallelism allowed between shown surfaces (I am talking about FOS surfaces, .650 size).