Self-referencing or not 1

[greenimi]

Fig 9-7 / ASME Y14.5-2009

If total runout defining datum feature D is replaced by position callout would you consider that the newly created position to be self-referencing (and hence not valid)?

Reasoning: I am thinking that position is checking the UAME and since D is secondary in the FCF than RAME is the one coming to play.

(Disclaimer: I am not saying that I would apply such callout, but I am just questioning its legality and validity, not its functionality)

 

[Burunduk]

perpetual and enduring painful and dire disagreements between 3DDave and you which are happening more often here, on this site, than I would like to

Well, I only disagree with 3DDave when he is wrong.

 

[greenimi]

Well, I only disagree with 3DDave when he is wrong.

He is saying the same thing!
The outcome is the same! Just back and forth.....

 

[Burunduk]

No, he does not say the same thing. Why do you say he does? Can you quote him saying that? I didn't disagree with him on this thread though.

You on the other hand, I don't understand what you are trying to achieve on this thread. You answered your own question at the OP when you mentioned the controlled UAME Vs. the RAME as a reference. Then it was confirmed by others. Then you really over-reacted over a mellow criticism claiming it gets in the way of discussing your point - which was already exhausted by then with nothing meaningful left to add. Dropping my name was a questionable move.

 

[greenimi]

No, he does not say the same thing. Why do you say he does? Can you quote him saying that?

Well, I only disagree with 3DDave when he is wrong.

So do you. You are "artificially" concluded that "only when he is wrong"! So you concluded (with or without merit) that he is wrong.

You on the other hand, I don't understand what you are trying to achieve on this thread. You answered your own question at the OP when you mentioned the controlled UAME Vs. the RAME as a reference. Then it was confirmed by others.

I already achieve and got the confirmation I needed in this thread. Thank you very much.

Dropping my name was a questionable move.

Dropping your name was before I've got confirmation I needed to be confident that I am on the right track.
And again, was done to avoid "being like" .....

 

[rimag]

Hi, I am working exclusively with ISO, but have seen examples from ASME Y14.5 in other threads on Calypso forum where they point to figures in Y14.5 that is a similar case where a datum is self-referencing. To me, its self referencing and not something that would be supported in ISO atleast. I am more familiar with the updated case that @SeasonLee showed from Y14.5-2018.

 

[3DDave]

In the proposed case the feature references a theoretical construct that isn't congruent with the feature. It's the use of the theoretical construct that severs the self reference.

This may not be what happens in ISO, but it is a primary concept in ASME Y14.5 references.

 

[Burunduk]

In ISO too, the datums that define a datum system are oriented relative to each other per their theoretical exact relationship. A secondary datum axis line would be exactly perpendicular to the primary datum plane. This would not be the case for the element being evaluated for position. So in the OP case, an ISO-compliant evaluation would not yield a measured value of zero, either.

In fact, because under ISO the evaluated element is an imperfect line and not the straight axis of ASME, the measured result is expected to indicate greater variation than per ASME.

 

[rimag]

I see now, that primary datum was C, not D my mistake. @Burunduk, I agree. Still, I am yet to see an example as such in ISO GPS standards.

The associated feature for the cylinder would be min circumscribed per ISO default rule and the situation feature being a straight line - axis of the associated feature. I assume that is different from Y14.5?

Thanks

 

[Burunduk]

The associated feature for the cylinder would be min circumscribed per ISO default rule and the situation feature being a straight line - axis of the associated feature. I assume that is different from Y14.5?

No, what you described would be the same in ASME, under different names. The "true geometric counterpart" of D would be the min circumscribed with a constraint of perfect perpendicularity to C, and the datum would be the straight line-axis of the "true geometric counterpart".

The difference would be in the element that has to fall into the position tolerance zone. Per ASME it would be the axis of the "unrelated actual mating envelope" - which is the straight line derived from an unconstrained min circumscribed cylinder of that feature.

 

[greenimi]

The associated feature for the cylinder would be min circumscribed per ISO default rule and the situation feature being a straight line - axis of the associated feature.

Rimag or anyone with knowledge,

Could someone with knowledge explain in laymen terms what a situation feature is in ISO and what is the equivalent term in ASME?
I am afraid I am not understanding what’s that about, hence my follow up question.

 

[rimag]

The difference would be in the element that has to fall into the position tolerance zone.

Thank you for clarifying. Overseeing the primary datum had me off there.

I am new to this forum and hoping to learn more about ASME and ISO similarities and differences.

 

[Burunduk]

Welcome rimag,
This forum is a good place to learn about ASME and ISO similarities and differences.

 

[3DDave]

Situation feature in ISO. See 3.2.5.1.2 on

https://www.iso.org/obp/ui/#iso:std:iso:22432:ed-1:v1:en

 

[rimag]

Could someone with knowledge explain in laymen terms what a situation feature is in ISO and what is the equivalent term in ASME?
I am afraid I am not understanding what’s that about, hence my follow up question.

ISO defines it in ISO 5459:2011 as a point, straight line or plane (or helix) from which the location and orientation of features can be defined.
A fully defined datum system locking all 6 DoF would consist of a set of situation features; normally a plane - a line and a point, derived from the associated features of the datum reference system. Much like how you would set up an alignment in CMM.

ISO 5459 has loads of examples in how different datum systems translates into combinations of these situation features.

 

[3DDave]

Is that identical to the definition I linked to? If not, how many definitions does ISO have for this one term?