Simultaeous requirements

[ringman]

Hypothetically:

I have a cylindrical part with tapped holes in different patterns on each end of the part. Assuming the part describes the OD as datum feature A and both end hole patterns are related only to A. Do simultaneous requirements apply to the patterns at the ends?


To add to this definition, lets omit the conventional vertical and horizontal CL from the drawing.

 

[powerhound]

Yes, they are considered a pattern and must meet their requirements simultaneously as long as both patterns are related to the same datum structure.

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[drawoh]

ringman,

Are you asking if the hole patterns at each end are related to each other, in addition to the OD?

Is this your drawing or are you fabricating or inspecting to someone else's drawing?

If they were my drawings and I cared about relating the holes at each end to each other, I would specify the extra datums and position tolerances required to achieve this. It is trivial to define one of the holes as a secondary or tertiary datum.

If I really did not care, I would place a note on the drawing explicitly stating that I did not care. It is hard to tell the difference between not caring about the holes, and not caring about the drafting.

In the absence of a specification locating the holes, I would assume that the holes are not located, and I would call the supplier and ask him to confirm this.

JHG

 

[powerhound]

While adding extra datums and such to make sure your intent is conveyed certainly won't hurt anything, it wouldn't be necessary and definitely not correct. The standard clearly addresses this very situation and considering the holes a pattern is the default. If you did not care about the orientation of the holes to each other, the explicit note you would state would be SEP RQT for separate requirement. This tells the manufacturer that each of the patterns has to meet it's tolerance separately. See paragraphs 5.3.6.1 and 5.3.6.2.

Whether or not the manufacturer actually knows about this is a different story. It's rare to find a shop that knows all the rules and implications that come with simply specifying that ASME standard as the standard to interpret the drawing to.

Here's another link that addresses the simultaneous requirements rule on the eng-tips website that I so frequently refer to. The Tip for March of this year addresses the issue of implications and things like that as well as commenting on the use of extra dimensions to specify what the standard already covers such as adding a half dimension from centerline to the edge of a feature when a positional callout alone already centers it.

http://www.tec-ease.com/tips/january-00.htm

Powerhound, GDTP T-0419
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Inventor 2008
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[ringman]

Powerhound,

The example that you cited illustrates some of my concerns and related questions. Firstly, if, as in the example there is only a single datum, which provides us with an axis, how can orientation relative to the axis alone be achieved? (In my opinion there can only be alignment with the axis) Secondly the standard specifies in 4.5.12, that if related to common datum FEATURES (plural).... they are considered composiite with simultanneous requirements.

I guess I am getting hung up on both basic geometry and the verbage of the standard somehow.

 

[Xplicator]

Ringman
You do understand the Implied 90° Basic Angle rule as found in 2.1.1.2 If the features are created/drawn to the same basic orientation and depicted as such on the spec and GD&T is invoked it is implied as a True Position wrt the datum specified.
So if they are pictorially represented on the drawing with one of the holes in either pattern being orientated either 0° or 90° from each other respectfully and the order of precedence of the datum specified in each FCF is identical, it is a simultaneous requirement unless otherwise specified. Keep in mind that an axial datum is not the axis alone but it is also associated to two theoretical planes intersecting at right angles. 4.4.2.

So in short, it is the orientation of one of these planes to the features on each end as drawn per the implied 90° rule that relates the two patterns together.

 

[powerhound]

ringman,
4.5.12 refers to composite FCF's. This is not what we're talking about here. I refer you again to 5.3.6.1 and 5.3.6.2.

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[powerhound]

Xplicator,

I've been pondering your explanation of simultaneous requirements invoked by the implied 90 rule and I don't understand how you've reached that conclusion. As I understand it, the simultaneous requirements rule is entirely independent of implied 90's and centerlines. Paragraph 1.4(j) requires the use of centerlines but the simultaneous requirements rule does not and in the OP ringman purposely omitted the use of centerlines. Even if centerlines were used, the features on each end of the cylinder would not be oriented 90 degrees in an end view, they would be aligned at 180 degrees. I hear this argument a lot and maybe it could be used via and extension of principle but it seems to be clear in the standard. An example is as follows:
Imagine a disc with 2 holes shown oriented 180 degrees apart, controlled by a FCF to the same datum structure, and there are centerlines through the disc and holes. What locks those holes at 180 degrees apart? Is it the implied 90 rule. I say no because they are not at right angles as is stated in the fundamental rule and also because in the absence of centerlines, the rule would not apply at all. It is the simultaneous requirements rule that controls them because it is in effect regardless of whether they are oriented at right angles to each other AND regardless of whether centerlines are used or not.
This tip is sort of close to what we're talking about:

http://www.tec-ease.com/tips/may-07.htm

Be sure to watch the video. It explains a little more than the read does.

Powerhound, GDTP T-0419
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Inventor 2008
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[Xplicator]

Hmmm, your really going to have to excuse me for what I am about to write it could be misconstrued as me being a little PO'd, wait a minute I think I am. I participate in this forum to be helpful to those looking for real solutions to real problems.

What's with this hypothetical OP? Is it for argument sake? OK, then I ask is there any logical reason whatsoever that centerlines would ever be omitted when depicting a cylindrical feature. Oh excuse me, I guess whomever created the Tec-Ease tip doesn't believe in Fundamental Rule 1.4b since there isn't even a dim/tol on the datum FOS referenced at MMC, not to mention absence of centerlines, they must not be needed. Additionally, I challenge anyone to find me one example in the entire ASME Y14.5M standard that doesn't include centerlines on each orthographic view of a cylindrical feature to depict it as such. If Fundamental Rule 1.4b is adhered to then there would be centerlines. Furthermore a centerline is needed to depict the geometric characteristic of the feature being cylindrical. Now since it is FOS, a diameter dimension and tolerance are also necessary to further define it.
He states in the OP that the FOS (OD) is the datum which the tapped hole patterns on each end are related to. However he fails to say just how they are related to the cylindrical feature of size. So for it to be a datum it must be referenced in a FCF as the DRF otherwise it means nothing. So let us presume, hypothetically of course, that position has been applied to each tapped hole pattern, again don't know how many make up the patterns or even what their basic orientation or location is to the referenced datum axis. OK once again one must speculate or presume because the OP or subsequent post do not clarify. I take that back apparently powerhound knows something the rest of us don't as he says in his last post

"Even if centerlines were used, the features on each end of the cylinder would not be oriented 90 degrees in an end view, they would be aligned at 180 degrees."

So lets go with that, it doesn't matter to me. If the tapped holes are 180° apart then there must be two of them on each end so not necessarily different patterns as stated in the OP. In any case in one of the end views one hole is depicted at lets say 12 o'clock the other at six. Datum A is a cylindrical datum feature and as such it is always associated with two mutually perpendicular planes that intersect at the axis of the feature. The centerlines on the end view depict the orientation of the theoretic datum planes, see Fig 4-5. Now lets look at 2.1.1.2 and 1.4j. Since the tapped hole features are depicted at the positions stated with GD&T applied and in absence of any basic angle dim other than 90°, the implied 90° is invoked and since these planes associated with the datum axis are mutually perpendicular, each quadrant of the cylindrical datum feature is basic 90° thus the two tapped holes are basic 180° apart. The reason I stated this wasn't so much for the simultaneous requirement as it was to educate ringman that this is a factor in the location and orientation of the tapped hole pattern as it relates to the datum specified and how they are depicted on the drawing. I hope you get the point and I don't have to speak of the pattern on the other end. The simultaneous requirement exist because there isn't a note stating them to be separate requirements, that was addressed with the second post in this thread.

That's really all I have to say on this topic. My hope is that at least some of you found this somewhat informative and useful, after all I believe our goal is one and the same to improve as a whole our use and understanding of the Y14.5M standard.

I would also like to add that the second Tec-Ease tip submitted is also incomplete. If I'm not mistaken Datum "C" referenced a tertiary must be located with a basic dim to the axis defined by datum feature "B" and subsequently to the hole that it is referenced to for it to be a legitimate spec.

 

[powerhound]

Xplicator,

You are a little on the defensive side if you let ANYTHING within this forum get your feathers ruffled. The participants will not always agree and when opposing views come along they should be treated as just that, not as personal attacks. I disagree with your interpretation of the implied 90 rule and I gave you my reasons as to why in an effort to add information to the mix. If you want to take that rule and read something into it that isn't there, that's fine. Some people reading this thread may agree with what I've presented and some won't. I won't apply the smackdown if they don't although I might re-post and reiterate if I think I haven't made my position clear enough.
The only time a centerline can be omitted is if it was present to begin with. I don't use software that automatically applies centerlines to either circles or cylinders as a default so unless you do, I'd like to ask for your logical reason for applying them to every cylindrical feature that you create.
The incomplete figure on the tec-ease website is irrelevant to your rant. The standard is full of incomplete figures that are used for purposes of illustration only. Will you then contend that the standard should be ignored because of it? You should read 1.1.4.
Regarding your last paragraph, you are mistaken. The hole is located using a FCF. This is now the time to use 1.4(i) or (j). The hole is located perp to A, basic to B and oriented to C. If centerlines were not used then you would be correct. Don Day is an ASME Y14.5M committee member and has written a section in the 2008 draft so maybe you should drop him a line and let him know that you've found an error on his website. His contact info is right there on his page.

Most of us use this forum to help where we can and contribute ideas to those who come asking, but we all need to be open to learning as well. I've been challenged on my views before and I've learned along the way as a result. You might find value in approaching your participation in the same light. It's already clear that if you find no value in a thread you will take the time to state that fact within the thread while making not a single contribution of value yourself (see Tolerance zone of R ambiguous thread). You just stepped in, declared it valueless, and made a grand exit by stating it would be your last post on the subject even though it was your ONLY post on the subject.

Lighten up Xplicator...

Powerhound, GDTP T-0419
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Inventor 2008
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[Xplicator]

Powerhound,

Please accept my apology, you are right, life is to short to let this forum get to me.

Regarding the Implied 90°, we agree to disagree.

I respectfully caution you or anybody out there to not rely on any software to be default Y14 compliant, regardless of claims. I come from old school and cut my teeth on the board with lead and paper. Where all line conventions were used to best communicate functional intent with the components clearly and effectively depicted. This always included centerlines and hidden lines, by default CAD systems today do not apply these unless your template and options have been set accordingly, in some cases you must simply add them. For example hidden lines do have significant value on drawings. However since CAD has become the dominant tool for creating all engineering drawings, some where along the way this usefulness has been lost and most all the drawings I see today are absent of hidden lines where if used the drawing would be a much clearer representation of the component and its features. This is a whole other topic. I am only using it as an example to make the point to not trust the default settings or base functionality of any CAD/CAM software please define your own "best practices" and ensure that they are compliant to ASME Y14.

Regarding the last example from Tec-ease, the C datum is not basically located. Again, no problem we can agree to disagree. Don can find his own errors.

Lastly, I will always try to contribute from my expierience and perspective, isn't that what we are all doing albeit I am not always tactful nor tolerant in my posts. I will make every effort to lighten up and be constructive.

Thanks and have a nice day!

 

[ringman]

I certainly never thought the question would cause this much controversy. But for the record, I will state or restate my opinions. From my recollections of geometry, there can be an infinite number of mutually perpendicular planes passed thru a line/axis. There then must be a point to define the 'orientation' of the one of these sets of planes before they may be used for measurement. I don't have the standard with me just now, but it states that for simultaneous requirements to apply there must be related to common datum FEATURES. (That is plural not just singular.) That point apparently was apparently missed in this discussion.

With regards to letting Tec-Ease, or any GD and T instructor go, on an error in his presentation is a mistake. IMHO

Thanks for the thought provoking comments from all.

 

[Xplicator]

In regards to the pluralism, it is my interpretation that per 4.2 and more specifically 4.2.2 that the DRF is not considered fully defined until sufficient datum features have been selected and referenced to lock it in six DOF or in essence immobilize the part to the three mutually perpendicular planes to properly establish the DRF or repeatable origin for measurements thus addressing the completeness as stated in 1.4b & 1.4c.

Furthermore to your question, it would seem as per the standard 4.5.12 that unless you have specified more then one datum feature in multiple FCF in the same order of precedence and identical material conditions for each, that it is not necessarily a simultaneous requirement.

However, as already mentioned one could argue the completeness of the spec since as you have witnessed right here in this thread, there is clearly more than one (mis)interpretation and disagreement.

In regards to outside cited works, I do not feel it is my responsibility to notify those responsible for errors in their works, since I was not the one citing them in the first place.

That's my 2 cents, hope to have been some help.