Simultaneous requirement 5

[DesignBiz]

In a previous thread regarding “profile and a datum”.

http://www.eng-tips.com/viewthread.cfm?qid=241508

A dwg was posted in support of the datums callouts. However as I looked at the dwgs from this post more closely I saw at the bottom a dwg with a different dimensioning scheme.

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

The link for the drawings claims the lower dwg is the same effect as the upper drawing dimension scheme, based on the simultaneous requirement. (pg 92 para 5.3.6.1 and 5.2.6.2 for the ASME Y14. 5M standard)

In the 1st (upper) dwg, a large hole in the center of a square part with a pattern of 4 holes located around a center hole is dimensioned to datums A (back surf of part); B (center hole); and C (height of part). Simple enough, however the bottom drawing shows the same part with the same callouts minus the B and C datums and claims this 2nd dimensioning scheme is the same as the 1st dimensioning scheme based on the “simultaneous requirement” rule.

I disagree. When datums B and C are taken away there is no datum to orient and locate the features to each other. The 2nd drawing only controls mutual perpendicularity to datum A, and the dimensional relationship to the pattern of 4 holes to each other. There is no longer any horizontal or vertical relationship to the features of the lower dwg as in the upper dwg.
I don’t believe this is a valid interpretation of the standards “simultaneous requirement” rule comparing these 2 drawings.

The lower drawing indeed shows a “simultaneous requirement” for all of it's feature callouts, however it is not comparable to the 1st or upper drawing.

Agree? Or tell me how am I incorrect.







DesignBiz

 

[ringster]

Design,

I agree with your statement as I understand it. Have you made commento to Tec Ease and if so, ressults?

 

[DesignBiz]

Ringster,

At this time, I was just looking for input/feedback as to what I may be missing or if others agree.

No comment at this point to Tec Ease. I have never contacted a forum member directly outside of thread posts.
As far as my experience goes, this is the place to review standard concepts and opinion; however if there is some protocol that I should be aware of then please advise.





DesignBiz

 

[ewh]

It can't be wrong! They are certified!

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[dingy2]

DesignBiz:

The Tec-Ease example shown does not comply with 5.3.6.1 & 5.3.6.2 on pages 92 & 93. The reference datum structure must be identical and not having one feature control frame only referencing datum A while other feature control frames referencing more than datum A. These are not simultaneous requirements under the 94 standard.

The ASME Y14.5M-94 standard supersedes interpretation examples as shown here by Tec-Ease.

Dave D.

http://www.qmsi.ca

 

[axym]

The Tec-Ease tip looks correct to me. There are no B and C datums in the lower drawing, but all of the features (and patterns) referenced to A are to be treated as a single pattern (as described in 5.3.6.2). This is a good example of the rule of simultaneous requirements.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[dingy2]

The second drawing in the Tec-Ease example does reflect simultaneous requirements but not the top drawing shown.

Maybe it is the verbiage that is confusing rather than the examples.

Dave D.

http://www.qmsi.ca

 

[DesignBiz]

I disagree Axym.

The link claims that the same hard gage could be used for both upper and lower drawings. No one can tell that without horizontal and vertical dimensions orienting and locating the features. If the center hole is over positive x and up positive y from the center of the outside profile; there are no dimension to indicate that or if they are centered. Just what are the tolerance of postion callouts in the lower drawing relative to regarding horizontal and vertical datums; or even to each other in the absence of datum references?

The simultaneous requirement does not state that what looks like a number of features sharing the same center, precludes us from providing dimensions for location and/or orientation.


The upper and lower dwgs could not use the same gage based on the simultaneous requirement in the standard.

DesignBiz

 

[axym]

Dave,

You're right, I think the intent of the verbiage is that only the lower drawing illustrates simultaneous requirements.

DesignBiz,

The first part of your objection relates to the "implied basic zero" issue that has been recently discussed in other threads. There is nothing on the drawing that explicitly indicates that the center hole is nominally 75 mm from the left hand side of the part. It's implied, because there are no dimensions showing otherwise. This is admittedly a gray area in the '94 standard. But it has nothing to do with simultaneous requirements.

The tolerance of position callouts define a "single pattern" of tolerance zones that are relative to each other. This extends the idea of a pattern to include groups of dissimilar features. All of the tolerance zones (and therefore the gage elements) have a basic relationship to each other. The relationship between any two features in the pattern (such as one of the holes relative to one of the edge features) is controlled indirectly.

This is hard to explain in words. A diagram is needed here!

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[PaulJackson]

DesignBiz,

The rule for simultaneous requirements makes all feature controls that have identical datum reference designations "one pattern". Since all the features in the pattern must be evaluated simultaneously or relative to one instantantaneous-common reference, their relationship to one another is not subject to any rotational or translational degrees of freedom. So the point that Don Day is making is true. All six degrees of freedom are always constrained among pattern features... the simultaneous requirements rule extends that constraint to feature controls that have identical datum references that are modified identically as well.

I believe that the intent rule in the beginning (82 and prior) was to insure that datum shift resulting from “datum features of size” could not be applied independently to feature controls that had identical datum references... however when the condition was described as “one composite pattern” it constrained all six degrees of freedom rather than just those that the DRF is capable of controlling. What is even more incredible is that simultaneous requirements apply to feature controls that have datum features that are not “features of size” in other words RFS… the reason… “a rocking primary datum surface”.
If two separate callouts both referenced to |A|B|C| “RFS” were verified independently and the primary datum because of its form deviation allowed it to rock… then the verifications could be subject to two unique |A|B|C| “RFS” datum references… hence the simultaneous requirement.

The only way to unlock this rule is with a “sep req’t” annotation or a control in the lower segment of a composite composite FCF.

Paul

 

[DesignBiz]

Axym,

Even if I were to buy in on the "implied basic zero" concept, the 1st and 2nd dwgs do not have the same DRF for the FCFs which along with the same material conditions required by the standard's definition of simultaneous requirement.

In this case it is obvious that the datums B and C are missing in the lower drawing's FCFs. This is in direct opposition to what the standard states.

As in the start of the thread and the last sentence in my post I acknowledge that the lower drawing has all features requiring conformance to the simultaneous requirement rule. My position is that the rule does not lend itself to the 1st and 2nd dwgs. They obviously do not have the same info in the FCF's.

Paul,
I do not disagree with you regarding the rule and orientation. Actually I do agree with your statemet,

"The rule for simultaneous requirements makes all feature controls that have identical datum reference designations "one pattern". "

The upper and lower drawings do not meet this requirement.

If the upper and lower drawings could fit the same simultaneous requirement then it would mean that the FCF's do not have to be identical.

DesignBiz

 

[axym]

OK, I think we've found the root cause of the problem.

The upper and lower drawings in the Tec-Ease tip are intended to be two completely independent examples.

The upper drawing shows a "conventional" approach with three datum features and other features referenced to them.

The lower drawing shows a different approach, with all of the features having identical datum references (to A) and therefore simultaneous requirements.

Nothing on the lower drawing is simultaneous with anything on the upper drawing, because the two drawings are not intended to exist together. It's one or the other.

The fact that Dingy2 and DesignBiz both interpreted the Tec-Ease tip that way indicates that it could have been worded more clearly.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[dingy2]

Evan:

I agree with your statement above about being different drawings. Although both might use the same gauge, one must use it in a different manner.

In the first example, we must qualify each datum individually and we certainly would not check any further if, as an example, datum B failed to meet the requirement.

In the 2nd example, we do check simultaneously since all are considered one pattern.

Dave D.

http://www.qmsi.ca

 

[DesignBiz]

Axym, ding2

agreed...

Yes, the wording can give someone a different impression other than the central intent.

agreed with ding2's comments on the gaging...

My thinking regarding the standard has been stimulated again. I had really never considered the "implied basic zero" including all features of a part. I had for a couple of features, but not the entire part.
To me, that example is a brain teaser.

DesignBiz

 

[MechNorth]

OK, just so I'm clear here before weighing in (Evan & Paul, nice explanations), everyone is ok that in the second example having only a single datum reference (Datum A) is adequate to fully constrain the wokpiece and all features as a single pattern? If so, consider a slight extension to that thought... if you have even a single feature on the workpiece which has SEP REQT on it, can you still get by with only a single datum reference?

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[PaulJackson]

That feature would be unconstrained for location relative to the composite pattern but it would be constrained for orientation relative to A and if it was the 4X pattern of holes they would still be constrained as its own pattern.

Without a location constraint the hole or hole pattern are free to wander to the edges or even breech the edges to the point where the measured size could be regarded non-conforming. It wouldn't be pretty.

Consider this however... If the 2.0+/-0.1 material thickness had a position callout on it |POS|0(M)| and the datum identifier "A" and its flatness note was removed as well as the the "A" from all the other callouts... Is it still "one composite pattern" without any datum reference?

Paul

 

[DesignBiz]

Okay, maybe I should be more reluctant but I'm game.

MechNorth,
No; no more single pattern, I dont believe so. The "Sep Req" would exclude that feature from the pattern. You would need another datum to locate it relative to the other features.

Paul,
I dont believe it is a fully defined positional control without a datum reference. I dont believe that removal of the flatness has much to do with removal of the datum reference nor the "0" at MMC callout, other than it would be flat within .2 . In the standard in 5.2.1.3 states that, it is "neccessary" to identfy features on a part to establish datums for dimensions locating true positions.

And now you've done it. After review of this paragraph (5.2.1.3) I am now not so sure about the "implied basic zero" that Axym brought up. Zero form what? what datum(s) is the zero from/to? I can accept the concept but now I want a datum to reference where the zero dim comes from!

DesignBiz

 

[axym]

DesignBiz,

The "implied basic zero" that I mentioned doesn't relate to datums. It's relates to basic dimensions. In the drawings in the Tec-Ease tip, the center hole looks like it is exactly in the middle of the hole pattern and there are no dimensions showing otherwise. So it is implied that the center hole is nominally supposed to be exactly in the middle.

The term "implied basic zero" is a bit misleading in this case. It applies better to things like features that look coaxial on the drawing, and therefore implied to be nominally coaxial. If a basic dimension were shown between the axis of one and the axis of the other, it would be zero.

It's the same kind of thing as the implied basic 90 degree angle.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[DesignBiz]

Axym,

1. That is my point. Actually coaxially is maybe a more easily viewed example. Before GDT and even in the 1973 standard when it was actually legal to attach a Datum symbol to the centerline itself, came the argument as to which of let's say 3 diameters is the Datum that the other 2 are located from. It was an argument long before GDT was widely accepted that features represented with a shared centerline meant that the centerline belonged to all of them. When identifying a datum in a FCF, it does identify which one. Even without the actual "zero" dimension by identifying the datums in a FCF, it gives me insight into part function; and how to setup for inspection.

2. How do you reconcile?

"In the standard in 5.2.1.3 states that, it is "neccessary" to identfy features on a part to establish datums for dimensions locating true positions."

One of the principles of a tolerance of position control is that it is measured by orienting a part the same way each time it is inspected. What if a number of parts are made by 3 different suppliers and inspected by 3 different suppliers. What says that all must use hard gage tooling to inspect the part? If another method is employed then how is the part garuanteed to be positioned the same way each time one is inspected in the absence of identified datums?


DesignBiz

 

[ringster]

Design,

When and where was it allowed to 'routinely' identify a CL as a datum?

I was unaware of that one.