Simultaneous requirements for patterns 5

[JacquesBeaudoin]

Hi,
Figures 10-38 and 10-47 of ASME Y14.5-2018 are showing a part with three different hole patterns.

I understand the aim of these two examples is to show the difference between Composite Frames and Multiple Single-Segments and this is well demonstrated.

The confusing part for me is about simultaneous requirements.

The position tolerance on each of the three patterns are using exactly the same datum reference frame.

The interpretation provided doesn't seem to link the zones of the three patterns together. Since there is no SEP REQT used on the feature control frames I would expect the three patterns of tolerance zones to be locked together.

Am I right?

 

[3DDave]

Yes. There are two datum reference frames. [A|B|C] for the upper ones and [A|B] for the lower ones. They do not have to use identical contacts for the [A|B...] part of each; that is, the part can be repositioned between checking the two sets of feature control frames.

 

[JacquesBeaudoin]

Thanks 3DDave for your quick reply, I'm afraid I'm still unsure of the answer. Are the three patterns locked together as a larger pattern or not? Your answer suggests not. Could you please explain why? Thanks.

 

[Garland23]

They are locked together as a larger pattern, simply because they use the same datum reference frame (and there is no MMB modifier on any datum references) for the upper position callouts.

The lower position callouts partially relate them to each other, but not completely because the left/right degree of freedom is not constrained.

So to answer your question, we have to distinguish between the upper and lower position tolerances of each.


(Edited to correct MMC modifier to MMB modifier.)

 

[3DDave]

They are linked together twice. The lower feature control frames moves them as a group that is tied together.

For the lower feature control frame they remain completely related to each other, just not to datum feature C.

 

[JacquesBeaudoin]

Hi Garland23,
You are saying that the second callouts are not simultaneous? I understand they can move right/left because the Datum Reference Frame does not include C. But my understanding is they can move right/left together as opposed to independently because the default is that all requirements using the same datum reference frame are considered as a single pattern. To allow them to move independently, the mention SEP REQT needs to be used.

 

[JacquesBeaudoin]

3DDave, I think we agree on the default simultaneous requirement when using same DRF with same BC. My problem is that in the standard fig.10-47, the interpretation suggests they are NOT tied up and can move independently right/left.

 

[Burunduk]

In the case of two single segments as shown in the embedded image (fig. 10-47), the 3 position controls with reference to A,B,C form a simultaneous requirement - all holes are locked together relative to the datum reference frame, and the 3 position controls with reference to A,B form a separate simultaneous requirement too - the different holes are partially locked to the datum reference frame and can only translate together in the unconstrained degree of freedom right-left.

In the case of composite feature control frames applied to similar geometry (figure 10-39), the lower segments of the 3 feature control frames do not form a simultaneous requirement, since lower segments of composites are explicitly excluded from simultaneous requirements. This means that the "play" each of the 3 groups of holes get in translation as part of the bottom segment refinements is unique and independent for each.

 

[JacquesBeaudoin]

Hi Burunduk, In fig 10-39, I don't understand how the second segment of composites are "explicitly" excluded from simultaneous requirements. Thanks.

 

[3DDave]

Suggests <> states. The "means this" fails to mention the 13 simultaneous tolerance zones for the upper callouts as well.

 

[3DDave]

What Mr. B. said is rote from the book, by definition.

 

[JacquesBeaudoin]

further reading of par 10.5.1 states: "Each complete horizontal segment in the feature control frames of Figures 10-39 and 10-40 should be verified separately." These figures are using composite.

so am I correct to say that the implicit simultaneous requirement (with same DRF & BC) only applies to the single feature control frames or multiple single-segments and that it does not apply to segments of a composite?

Thanks again.

 

[Burunduk]

so am I correct to say that the implicit simultaneous requirement (with same DRF & BC) only applies to the single feature control frames or multiple single-segments and that it does not apply to segments of a composite?

It doesn't apply to the lower segments of composites, just to the top segments. Look up the definition of a Simultaneous Requirement in section 7.

 

[JacquesBeaudoin]

Thanks Burunduk, nailed it.

Par 7.19
This principle does not apply to the lower segments of composite feature
control frames. See para. 10.5.4.2. If a simultaneous
requirement is desired for the lower segments of two
or more composite feature control frames, a notation
such as SIM REQT shall be placed adjacent to each applicable
lower segment of the feature control frames.

 

[Garland23]

JacquesBeaudoin...the given example that you posted in the question is not composite position; yours gives two position symbols. So that paragraph doesn't apply. I'm not sure if that's what you were saying before Burunduk quoted the paragraph.

However, I need to correct my post! I think 3DDave was correct in his post from 20 Jul 23 02:17. Even though the lower FCFs lack datum C, they still link all holes and all patterns to one another in every direction because of the simultaneous requirements rule.

 

[Burunduk]

Garland23,
The OP mentioned two examples from the standard - both with the same part geometry, one with composite position tolerances and the other with two single segments. The embedded picture in the OP shows only the two single segments solution, but I believe he was interested in understanding how simultaneous requirements relate to both, especially considering how the discussion evolved. The paragraph I directed him to clarifies exactly what he has been asking about at 20 Jul 23 02:46.

 

[Garland23]

Fair enough. So to be clear, if it's composite position, then the lower position tolerances do NOT relate the patterns to each other. But if it's two single segments, the lower position tolerances DO relate the patterns to each other in all directions.
Would that be a good summary?

 

[3DDave]

Yes - that is a good summary.

 

[axym]

JacquesBeaudoin,

I agree that in 10-47 the 3 lower segments form a simultaneous requirement. The 13 lower segment zones are simultaneous with each other as 3DDave said.

I would also agree with you that the "means this" figures you posted suggest that the zones for each pattern can move independently right/left. I would go further and say that these figures are very misleading. Each figure says "one possible displacement of actual feature pattern", which is technically correct.
Each one is one possible displacement. But it doesn't mention that both of these displacements could not be used on the same actual part. In fact, there is no mention of simultaneous requirements in the text or figures for 10-47 at all. I believe that this omission was unintentional, but I would say that it has contributed to the ongoing confusion over pattern control and simultaneous requirements.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca