Orientation controls referencing 2 datums 2

[Sem_D220]

What are the opinions on the following schemes?

1. Angularity control referencing 2 datums in the FCF, when the basic angle is specified between the controlled face and the secondary datum. The primary and the secondary datums are perpendicular to each other.

2. Parallelism control referencing 2 datums in the FCF, when the controlled face is nominally parallel to the secondary datum and perpendicular to the primary datum.

3. Perpendicularity control referencing 2 datums in the FCF, when the controlled feature is nominally perpendicular to the secondary datum and at some other angle to the primary datum.

I haven't seen any of these brought as an example in the Y14.5 standard (unless I'm missing one), or in any other sources I was exposed to, but I also don't see how the contents of chapter 6 may reject those schemes. Schemes #1 and #2 are ones I wanted to implement for real cases, but hesitated (eventually I did ). As for #3, I haven't encountered a case requiring this, but I can imagine one. I think I once heard a GD&T professional say that there should always be a basic implied 90° angle (for perpendicularity), or a basic angle of some other value (for angularity) between the controlled feature and the primary datum feature whereas the secondary datum may only constrain DOF / orient the tolerance zone. But, if the DRF should first and foremost reflect the functional interface, there certainly may be cases where a vice-versa scheme is justified. The problem is - there are no figures to point to if such position needs to be supported. In Y14.5, looking for orientation controls that reference more than one datum, I find only figures 6-4, 6-8, and even 6-17, all show an implied right angle relationship or basic angle between the controlled feature and the primary datum reference, never to the secondary.

Has anyone else dealt with this dilemma? Maybe it's only my lack of knowledge / experience, and such schemes are either commonly practiced or clearly not supported? Whatever the case is your input will be very much appreciated.

Edit: I'd like to add that I realize that one solution could be to use profile of a surface for orientation, but from various reasons I prefer to utilize orientation controls and reserve this solution only as a last resort, if needed.

 

[pmarc]

If everything so far sounds reasonable, imagine that the 60° angle was changed to 0°, and the symbol was changed to parallelism. Would that control loose it's legitimacy in that case?

I guess you meant: If everything so far sounds reasonable, imagine that the 60° angle was changed to 90°, and the symbol was changed to perpendicularity. Would that control loose it's legitimacy in that case?

If that is true, may I ask what would that give you?

 

[CheckerHater]

@powerhound: sorry; 7-45 was the illustration that pmarc had very low opinion of in thread1103-441690.

@pmarc: I quoted Y14.5.1.M Para. 6.6.1 today to argue that datum order has a meaning.

@Sem D220: When and where did I call datums separately, with disregard to DRF?



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

 

[pmarc]

CH,

I know that you quoted para. 6.6.1 of Y14.5.1M earlier today, but I am wondering what exactly in that paragraph makes you think that for angularity the toleranced feature should be at a basic angle other than 0 or 90 degrees to the primary datum plane.

 

[Belanger]

pmarc -- you wrote that Fig. 4-7 contradicts CH's claim that

"Basic angle must be specified between the controlled face and the primary datum."

But according to paragraph 2.1.1.4, the angularity tolerance in Fig. 4-7 does have a basic angle w.r.t. datum A; it's just not displayed.
Or are you picking on the word "specified"?

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

 

[pmarc]

If I understand CH correctly, he thinks that it is not the angularity symbol that should be used in fig. 4-7 in the FCF applied to datum feature C but rather perpendicularity symbol, because that is the only possible orientational relationship between the toleranced feature and primary datum plane A. In other words, in order to properly apply angularity symbol the toleranced feature must be at a basic angle different than 0 or 90 degrees to the primary datum. He quoted para. 6.6.1 from the math standard to support this.

I say that para. 6.6.1 in Y14.5.1M merely says that the toleranced feature must be basically oriented to the primary datum. It does not say that the basic angle must be other than 0 or 90 degrees.

So I guess it is about the word "specified", but I am more picking on CH's interpretation of the paragraph that he used to support his standpoint. And I am even more against using para. 1.1.4 in a way it was not designed for.

 

[pylfrm]

Sem_D220,

If you want an orientation tolerance with a secondary datum feature reference, I'd highly recommend using angularity. Anything else is asking for trouble in my experience.


pylfrm

 

[Sem_D220]

When and where did I call datums separately, with disregard to DRF?

Then refine for parallelism to C and also angularity to A if needed, or just refine with angularity alone to C and A

CH, If I understand it correctly, the first suggestion in the last quote above is about controlling parallelism and angularity separately to single datum references, and the second suggestion is exactly what I suggested by scheme #1, which you consider wrong (?)

I guess you meant: If everything so far sounds reasonable, imagine that the 60° angle was changed to 90°, and the symbol was changed to perpendicularity. Would that control loose it's legitimacy in that case?

If that is true, may I ask what would that give you?

You are right, changing the symbol to perpendicularity and the angle to 90° represents the issue better. To your question, it would give me the intended 90° orientation control, with the DRF datum precedence order according to functionality. Changing the symbol to parallelism in that case would result in exactly the same tolerance zone, but will not serve design intent clarity well if what is intended is actually to control the 90° relationship as a main goal.

pylfrm, it seems that even with regard to angularity not everyone is in agreement (it was claimed that the basic angle to be controlled must be specified to the primary datum always). Perhaps what is left is only profile of a surface?

 

[pylfrm]

Sem_D220,

The basic orientation of the toleranced feature with respect to all referenced datum features must be specified. Has anyone suggested otherwise?


Edit: Corrected spelling of username. Why the new account, by the way?

 

[Sem_D220]

pylfrm - this is what I was talking about - CH commenting about scheme #1 from the opening post:

1. Angularity control referencing 2 datums in the FCF, when the basic angle is specified between the controlled face and the secondary datum. The primary and the secondary datums are perpendicular to each other. - WRONG. Basic angle must be specified between the controlled face and the primary datum

That means the angularity control shown in fig. 4-7 in Y14.5 is also controversial. The rejection follows the same logic which is behind denying legitimacy of the other schemes.

 

[pylfrm]

Sem_D220,

In ASME Y14.5-2009 Fig. 4-7, the basic orientation of datum feature B with respect to datum feature A is fully specified by the implied 90° angle. The basic orientation of datum feature C with respect to datum features A and B is fully specified by the implied 90° angle and the 60° dimension.


pylfrm

 

[Sem_D220]

pylfrm,
Objections to schemes in this thread are not over lack of specification or lack of basic orientation between datums. It is over datum precedence order in feature control frames.

 

[pylfrm]

Sem_D220,

My objection to your scheme 1 is due to the implied lack of specification of basic angle between toleranced feature and primary datum feature. As I explained, Fig. 4-7 does not have this problem. I have no objection to your scheme 1 related to datum precedence.


pylfrm

 

[Sem_D220]

My scheme #1 is exactly what is shown in fig. 4-7. Perhaps the literal description doesn't stand on it's own well enough without an accompanying diagram. Sorry about that. I didn't notice fig. 4-7 as an exact reference until pmarc mentioned that figure.

 

[pmarc]

To your question, it would give me the intended 90° orientation control, with the DRF datum precedence order according to functionality. Changing the symbol to parallelism in that case would result in exactly the same tolerance zone, but will not serve design intent clarity well if what is intended is actually to control the 90° relationship as a main goal.

Based on my experience, I am pretty sure that changing the symbol to perpendicularity would serve as design intent clarification only to you and to people that you were able to reach and directly explain the intent. For everyone else this would only cause a confusion. I think the discussion we all are having now is sufficient proof of that.

So like I said at the beginning, per my knowledge there is nothing (rightly or not is a different story) in the standard that could really stop you from doing what you want to do (especially if you use fig. 4-7 as a backup), but if you really care about clarity of the callout, I would recommend to think twice before deciding to go this way.

Just like I would think twice before applying perpendicularity symbol instead of angularity for datum feature C in fig. 4-7, even though it is against my belief/logic that in case of other two types of orientation controls - that is perpendicularity and parallelism - the selection of proper symbol should be determined by the relationship between the toleranced feature and primary datum.

 

[Sem_D220]

pmarc,
I definitely understand the main message of your last post. As stated before, I'm aware it's a problematic concept, but I don't want to compromise on functional DRF just to make the symbol specified as everyone is used to. I hope that using angularity the way it is used in fig. 4-7 (when the main goal is to control the 60° angle to the secondary datum and not perpendicularity to the primary) is acceptable by most. By your last post I conclude you are not against such use. In that case it could be a solution to all orienration controls where the required datum precedence is in conflict to how perpendicularity/ parallelism symbols are expected to be used.

 

[CheckerHater]

Sem D220,
Do I understand you correctly that in your "real life" application you have to establish DRF once and then follow the same order of precedence in all your controls?
You don't have to do that. You can control some features to A|B|C and others to C|A|B. It will not violate the standard.
pmarc,
According to the standards, both Y14.5 and Y14.5.1, all orientation controls are exactly the same, the difference is only the value of the basic angle.
There is none and there cannot be any difference in the way perpendicularity, angularity or parallelism is applied.
So you have to pick either side:
If you "believe that in case of perpendicularity and parallelism callout the symbol used in the FCF should match the relationship between primary datum and the toleranced feature", you have to extend your belief towards angularity as well.
Or 4-7 approach should equally apply to all cases of orientation.
I could agree though that on 4-7 angularity serves as perpendicularity control first and 60 deg. angle control second.

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

 

[CheckerHater]

It looks like we are getting stuck being attached to our different ways and ignoring the big picture. I wanted to ask some general question but I don’t want to hijack the thread, so I decided to start afresh.
Everybody is invited to the new thread thread1103-442354 which I think may help us to understand our differences better.
Thank you


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

 

[Sem_D220]

CH,
I do know I don't have to apply the same datum precedence order for all controls. But I want the part oriented in the fixture for inpection inspection the same as it's oriented at real application assembly. It is not about violating the standard or not. I don't think that the kind of control I use should determine the datum precedence order. It is the part functionality that should determine it for whatever control is under consideration. There is no reason to exclude orientation controls out of this basic design principle.

 

[CheckerHater]

Sem D220,
Let's go back to my "door" example.
Everything in your room is related to floor|wall|wall (A|B|C)
Then you say "the door is open 45 deg from the wall". Does it violate the function of the door? You may add "and door is always perpendicular to the floor", but make it secondary.
We are forgetting the very basics - the original definition of the word "datum". Datum is your reference point, it's what you measure from. We measure angle between the door and the wall - we measure from the wall.
Nevertheless - I am starting new thread to get "back to basics". Maybe we can look at the same problem from the different angle (no pun intended )

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

 

[Sem_D220]

CH,
I say that if there is a chance that |wall|floor| control will accept a door installation that would be rejected by |floor|wall| control or vice versa - it is better to aply a |floor|wall| DRF for controlling the 45° angle (I really hope I'm not making a structural engineering mistake here )