Perpendicularity tolerance as refinment of Concentricity tolernce 2

[waqasmalik]

Is perpendicularity tolerance is a refinement of concentricity and symmetry tolerance?
To me, perpendicularity tolerance is a refinement of position tolerance, run out and profile of surface.

 

[asmeY145Manswer]

As you can see, I prefer easy. I don't like difficult too much!

 

[powerhound]

Cylindricity also is never referenced at MMC.

In other words, imagine this cylinder feature is protruding from a flat plate which represents my primary datum A.
What's to say that it doesn't protrude out at some obtuse angel from the plate, which it will do in reality?
There is noting yet that controls the perpendicularity of Datum axis B to Datum A.

The standard says that datum axis B will be perpendicular to datum A. The perpendicularity of the datum features to each other is either controlled by an appropriate GD&T callout or by the implied 90 rule, NOT by cylindricity. This really has nothing to do with cylindricity so I don't even know why you asked the question.


John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[asmeY145Manswer]

Wrong, and very wrong!

There is no 'implied rule'. The perpendicularity of datum feature A must still be controlled wrt datum axis B. Your cylindricity requirement does not specify that.

That is why you need the refinement. Because if you never specify how A is related to axis B, then you never control this relationship!

 

[asmeY145Manswer]

And remember datum axis B was established by the cylindrical feature. We just happened to call out a cylindricity for it. But we never said how perpendicular it needed to be to datum feature A.

 

[asmeY145Manswer]

Can you see how it is possible to meet the cylindricity requirement, but still not be perpendicular, as we would like it to be?

 

[asmeY145Manswer]

And John,

Thanks for your service! I am just trying to demystify the subject. Hope I can help you!

 

[powerhound]

In both the 1994 standard and the 2009 standard fundamental rules 1.4(i, and j) clearly define the implied 90 rule. So that means there IS such a rule.

The perpendicularity of datum feature A must still be controlled wrt datum axis B.

This is different from what you originally said. I can agree with this.

Can you see how it is possible to meet the cylindricity requirement, but still not be perpendicular, as we would like it to be?

Of course I can. That was never even in question. I'm not sure where you're getting this idea that I'm somehow confused about it.

Is it possible that a cylindrical feature could be cylindrical wrt a datum axis established by that datum feature at say MMC

As far as demystifying the subject; suggesting examples of cylindricity wrt to a datum and modified at MMC is pretty mysterious in itself.

Hopefully we can all help you.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[asmeY145Manswer]

New Post powerhound (Mechanical)
4 Dec 13 11:23
In both the 1994 standard and the 2009 standard fundamental rules 1.4(i, and j) clearly define the implied 90 rule. So that means there IS such a rule.

Great!

But only for a theoretical datum reference frame is this true (chapter 4). And that is all very theoretical now. Isn't it. But you still have to relate features to those datums. And you still have to establish datums with features. Points of tangency contact for a primary, for example, two points for a secondary, and so on. So if you never do that, and you just assume on a drawing that your datum features are always 90 degrees perpendicular, well, there is no equipment on the planet, known to man, that can help you to find three orthogonal datums that are 90 degrees to each other, and measure anything against that. This is the real world! So the goal here is only to relate features to one another, not to try and do the impossible!

New Post powerhound (Mechanical)
4 Dec 13 11:23
This is different from what you originally said. I can agree with this.

Thankyou! But read on.

New Post powerhound (Mechanical)
4 Dec 13 11:23
Of course I can. That was never even in question. I'm not sure where you're getting this idea that I'm somehow confused about it.

Well, I started out trying to answer the question that was asked by someone at the start of this thread that asked something like, why did a cylindricity requirement need a perpendicularity refinement, or something to that effect.Right? So yes, that did appear to be in question. Now I am sure that You understand that. Because you have told me so. But.. I just didn't see your correct explanation here on this thread anywhere. And that is the mystery for me tonight!

New Post powerhound (Mechanical)
4 Dec 13 11:23

As far as demystifying the subject; suggesting examples of cylindricity wrt to a datum and modified at MMC is pretty mysterious in itself.

Hopefully we can all help you. bigsmile

And you are probably right. I probably need lots of help for a lot of different reasons. But that's outside of the scope of our discussion! Fair is fair!

See now, you thought I meant something that I didn't mean, and that I said what I meant, and that was what you understood it to mean, and it wasn't meant at all, and it wasn't the way you understood it. And now you have an interpretation problem! My bad! The feature was establishing the datum axis, the cylindricity was not, and that was the problem. Hence my answer to the thread. Got it? And it is necessary sometimes to speak conceptually on this forum, because we are not really looking at drawings, we are only trying to explain concepts.

Interesting, isn't it, how ASME Y14.5M is supposed to communicate clearly a designer's intent? Yet I find there is a lot of confusion out there, even amongst some of the best engineers!

So have you learned anything now tonight? And Relax! How is the weather out there where you are stationed? Stay safe, and please respond. (I don't know how to add a smiley to this thing. Hopefully it works).

 

[powerhound]

Well it looks like the big misunderstanding is what you were responding to. The original question was if perpendicularity was a refinement of CONCENTRICITY, not cylindricity. This explains what appeared to be an unrelated tangent. I was wondering why cylindricity was suddenly an issue.

But only for a theoretical datum reference frame is this true (chapter 4).

The implied 90 rule has nothing to do with any datum reference frame, theoretical or not. Help me understand why you say the implied 90 rule only applies in such a case.

So if you never do that, and you just assume on a drawing that your datum features are always 90 degrees perpendicular, well, there is no equipment on the planet, known to man, that can help you to find three orthogonal datums that are 90 degrees to each other, and measure anything against that.

The implied 90 rule uses the default angular tolerance so it's not assumed to be a basic 90. The standard says that a datum reference frame is made up of three mutually perpendicular planes. They are all oriented at a basic 90 degree angle to each other. Datums are perfect, datum features are not. Datum simulators are as close to perfect as possible and we accept that they are close enough to perfect to be considered perfect, even though we know that they really aren't. Parts are checked on surface plates and angle plate every day. Gauge pins are used to check hole diameters and to establish datum axes every day. We do not find datum planes, we establish them with datum features and datum simulators.

And you are probably right. I probably need lots of help for a lot of different reasons. But that's outside of the scope of our discussion! Fair is fair!

Your reference to cylindricity at MMC wrt a datum is within the scope of what we're talking about because it's what drew me into the thread to begin with and you seem to be defending your position on it since you are not backing off of it or acknowledging that you were wrong about it. Do you really think this is a GD&T legal callout?

See now, you thought I meant something that I didn't mean, and that I said what I meant, and that was what you understood it to mean, and it wasn't meant at all, and it wasn't the way you understood it. And now you have an interpretation problem!

Here's what you said:

Is it possible that a cylindrical feature could be cylindrical wrt a datum axis established by that datum feature at say MMC...

"cylindrical wrt a datum axis..." <==this says you think cylindricity can be referenced to a datum.

"at say MMC..." <==this says you think cylindricity can be modified at MMC.

So what is it that I'm misinterpreting...or do you think these things can actually be legally done?

Interesting, isn't it, how ASME Y14.5M is supposed to communicate clearly a designer's intent? Yet I find there is a lot of confusion out there, even amongst some of the best engineers!

I can assure you that while I still don't know every single thing in the standard, I'm not the least bit confused about anything you and I have discussed.


John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[asmeY145Manswer]

And now just imagine, that you are charged with the task of designing an absolute/ practical absolute guage, just to measure all this nonsense! Where would you start?

 

[asmeY145Manswer]

New Post powerhound (Mechanical)
4 Dec 13 23:01
Well it looks like the big misunderstanding is what you were responding to. The original question was if perpendicularity was a refinement of CONCENTRICITY, not cylindricity. This explains what appeared to be an unrelated tangent. I was wondering why cylindricity was suddenly an issue.

[highlight #EF2929]I think it is very important to understand the difference between cylindricity, concentricity, coaxiality, circularity, runout, and total runout. The point I was making was simply that total runout is much easier to measure. If you don't need cylindricity (and look at what those things mean in the standard), then why use it, and that is difficult and very expensive to measure. You will need expensive CMM equipment to do that. And it is debatable if that even does the job right. OK? Total Runout can easily be measured with a dial indicator.[/highlight]

Quote:
But only for a theoretical datum reference frame is this true (chapter 4).


The implied 90 rule has nothing to do with any datum reference frame, theoretical or not. Help me understand why you say the implied 90 rule only applies in such a case.

Quote:
So if you never do that, and you just assume on a drawing that your datum features are always 90 degrees perpendicular, well, there is no equipment on the planet, known to man, that can help you to find three orthogonal datums that are 90 degrees to each other, and measure anything against that.


The implied 90 rule uses the default angular tolerance so it's not assumed to be a basic 90. The standard says that a datum reference frame is made up of three mutually perpendicular planes. They are all oriented at a basic 90 degree angle to each other. Datums are perfect, datum features are not. Datum simulators are as close to perfect as possible and we accept that they are close enough to perfect to be considered perfect, even though we know that they really aren't. Parts are checked on surface plates and angle plate every day. Gauge pins are used to check hole diameters and to establish datum axes every day. We do not find datum planes, we establish them with datum features and datum simulators.

Can you do me a favor? Can you read ASME Y14.5 M either 2005, or 2009, Chapter 4, first page to last page, (because they are very different now, MMB as opposed to MMC), and just see, and understand how we establish a Datum Reference Frame. You must do this with features, usually, the features that are most critical to function. Your datums, such as they may be, can only be established by features. And that will never be perfect. But at least now, you can establish the relationship of one to the other within a tolerance, and that can now be directly measured. Right? Now, every other feature on your part will reference those datums that you just established. And they will be related to such, according to whatever tolerance you specify, and can now be similarly measured.[highlight red][highlight #EF2929][/highlight][/highlight]

Quote:
And you are probably right. I probably need lots of help for a lot of different reasons. But that's outside of the scope of our discussion! Fair is fair!


Your reference to cylindricity at MMC wrt a datum is within the scope of what we're talking about because it's what drew me into the thread to begin with and you seem to be defending your position on it since you are not backing off of it or acknowledging that you were wrong about it. Do you really think this is a GD&T legal callout?

[highlight #EF2929]NO, ABSOLUTELY NOT[/highlight]

Quote:
See now, you thought I meant something that I didn't mean, and that I said what I meant, and that was what you understood it to mean, and it wasn't meant at all, and it wasn't the way you understood it. And now you have an interpretation problem!


Here's what you said:

Quote:
Is it possible that a cylindrical feature could be cylindrical wrt a datum axis established by that datum feature at say MMC...


"cylindrical wrt a datum axis..." <==this says you think cylindricity can be referenced to a datum.

"at say MMC..." <==this says you think cylindricity can be modified at MMC.

So what is it that I'm misinterpreting...or do you think these things can actually be legally done?

NO. Cylindricity is nothing like a positional tolerance. And you are correct about that![highlight #EF2929][/highlight]

Quote:
Interesting, isn't it, how ASME Y14.5M is supposed to communicate clearly a designer's intent? Yet I find there is a lot of confusion out there, even amongst some of the best engineers!


I can assure you that while I still don't know every single thing in the standard, I'm not the least bit confused about anything you and I have discussed.

That is great news! And I am honored! OK?[highlight #EF2929][/highlight]

 

[asmeY145Manswer]

The big red mark in the middle was supposed to say 'NO, ABSOLUTELY NOT'.

 

[asmeY145Manswer]

But, Can a cylindrical feature establish a datum axis? Yes. And can a feature control frame somewhere in that drawing reference that datum at say MMC? Now, what does that mean, say you?

Now why can't I just go ahead and refine that feature to be within a cylindricity tolerance (in most cases, I would never do this)? And that actually, has nothing to do with anything I said before. It is totally unrelated.

But it is legal, and, it is also because I determined, that that was important for my design! For some reason! Right?

 

[asmeY145Manswer]

The significance of that is when you come to make a guage for it. Sorry folks! I am tired now, but I will explain more tomorrow.

 

[greenimi]

Gentlemen,

I am really confused about the discussion between ASMEy14.5manswer and powerhound.

I don’t take sides, but I am wondering that this discussion has to do with the OP. The OP is probably learning for the GD and T certification test or learning GD an T from AK book for his own edification and he has a question about some statements AK makes in his Fundamental book.

I don’t know why cylindricity shows suddenly up into the conversation, why the total runout is the preferred inspecton method and also why the 90° degress implied angle landed into this mess too.

No wondering why pmarc and Evan (to name a few) bail out from this conversation

I am not drunk or not even tired (not yet on both), but sorry guys I don’t understand………

 

[ewh]

Yes, this thread has gone into the weeds a bit.

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

 

[powerhound]

Yeah, sorry guys. This has gone too far. I thought it would be a matter quickly resolved with one or two posts. This reminds me of the DrCADD thread from a couple of years back.

I'll bow out and let this thing die.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[greenimi]

I read DrCADD thread you mentioned. Glad DrCADD didn’t mess up my GD and T training (not his student)

You have to be careful who you are debating/talking to, as you never know when one of his former students might show up one day and dispute some concepts.

 

[CheckerHater]

Are you trying to say asmeY145Manswer is DrCADD's student?

 

[asmeY145Manswer]

Sorry folks!

I'm out of it too. And yes it really did end up in the weeds. And that's not constructive.

Better to keep it to one question, and one answer. But it is a complicated subject!

And thank God I don't know any evil Dr CADD. Because if I was his student, then he would have to be a very old man by now.

He was probably the guy that graded me on the quality of my pencil lines, and my stenciled letters. And that was a long time a go - to some of you kids!