×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Correct or not? And how to inspect?

Correct or not? And how to inspect?

Correct or not? And how to inspect?

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

Thank you
Gabi

RE: Correct or not? And how to inspect?

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

RE: Correct or not? And how to inspect?

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.

RE: Correct or not? And how to inspect?

@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

RE: Correct or not? And how to inspect?

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.

RE: Correct or not? And how to inspect?

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

RE: Correct or not? And how to inspect?

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?

RE: Correct or not? And how to inspect?

Based on this very old picture, http://files.engineering.com/download.aspx?folder=...

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

RE: Correct or not? And how to inspect?

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

RE: Correct or not? And how to inspect?

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

RE: Correct or not? And how to inspect?

Ah. Okay.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

RE: Correct or not? And how to inspect?

John,
What is 'Derived Center Plane'? 😉

RE: Correct or not? And how to inspect?

RE: Correct or not? And how to inspect?

What does "DMPF" acronym mean?

Tunalover

RE: Correct or not? And how to inspect?

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

RE: Correct or not? And how to inspect?

(OP)

Quote (CheckerHater)

“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

RE: Correct or not? And how to inspect?

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

RE: Correct or not? And how to inspect?

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?

RE: Correct or not? And how to inspect?

Once again, no

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

RE: Correct or not? And how to inspect?

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).

RE: Correct or not? And how to inspect?

Quote (CH)

Only size tolerance will control parallelism
Only if Rule#1 is in effect.

If rule#1 is not (since in my example I have added DMLF) then how is the parallelism controlled direct or indirect?
That is my dilemma.


RE: Correct or not? And how to inspect?

I think that flatness of the derived median plane idea was offered in case the max. material modifier in the geometric tolerance window was thought necessary for the design intent of the part. I believe that the quickest way to check the flatness of DMP (at circle M) is with a full form functional gauge (bridge gauge). With the .500 dia. protrusion on the top of the part this inspection might get slightly more costly. It also should be noted that rule #1 does not apply to FDMP.

RE: Correct or not? And how to inspect?

@greenimi:

Why exactly you want to control parallelism without using parallelism control?

Doesn't make lot of sense even from purely academic point.

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

RE: Correct or not? And how to inspect?

Quote (CH)

Why exactly you want to control parallelism without using parallelism control?

To learn more about all of these controls/callouts. And to avoid redundant callouts on the drawings.
To see and understand the "unintended consequences" of some GD&T callouts. --direct versus indirect relationship between features---

RE: Correct or not? And how to inspect?

IF FDMP had been specified and was also called out as a datum feature would the datum be the derived median plane or the center plane? Or are they the same in this instance?

RE: Correct or not? And how to inspect?

AndrewTT,

In my hypothetical case I don't have a datum feature (only DMPF and size dimension). Remember: the OP question has been answered and I am building additional or revised constrains and /or questions based on his original thread.

Also what is that "center plane"? (maybe wrong nomenclature) This question has been asked before.

RE: Correct or not? And how to inspect?

Also I would say DMPF is an imperfect plane/ surface and the "center plane" is AME meaning a perfect plane

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources