Defining a datum in a 2X detail view

[Yuyu28]

I have the following drawing of the grooves on a shaft that hold retainer rings. I know it is not fully constrained, but that is not relevant to the question.

Context:
a) FUNCTION: The shaft fits with clearance into two holes to constrain two other parts radially. The axial movement is constrained by the retainer rings.
b) The tolerances specified are given by the retainer ring specifications, and the rest are controlled by general tolerances.
c) The concentricity tolerance is important only between the groove and the far-side/shorter cylindrical FOS of the shaft, not between the groove and the longer FOS.
d) The shaft length is 210mm.
e) We are working with ISO 1101:2012.

My questions are:
1) Is it valid to define datum A in a detail view that has a 2X note under it? Would that mean that there is another datum (A'? B?) implied at the other end of the shaft, or would that require a note like "EACH" or "2X" under the datum feature symbol?

2) If there is not a second "implied" datum, how would one unambiguously control the concentricity of the groove on the other side? Would it be necessary to create a second detail view on that side, defining datum feature B there? I thought of removing the 2X from the detail view label and putting it on each of the dimensions, but that can lead to controlling one groove's concentricity w.r.t. the FOS on the other side.

EDIT: added function for clarification.

 

[chez311]

Yuyu28,

Since nobody has responded yet I'll take a crack at it. As a disclaimer I am not extremely well versed in ISO however hopefully I can provide some insight.

The concentricity tolerance is important only between the groove and the far-side/shorter cylindrical FOS of the shaft, not between the groove and the longer FOS.

Why? How does this part mate/function that this is the case? As currently shown your feature specified as datum feature A would be a poor reference on its own - that tiny sliver at the end of the shaft (made even shorter by a chamfer) will be unreliable at best. Perhaps ISO has something equivalent/similar to ASME's <CF> (continuous feature) symbol to treat the interrupted shaft OD as a single feature that could be utilized (perhaps ISO's UF or United Feature) and/or a chain line or similar could be utilized to show only a portion of the side opposite the groove forms datum feature A instead of its full length.

Is it valid to define datum A in a detail view that has a 2X note under it? Would that mean that there is another datum (A'? B?) implied at the other end of the shaft, or would that require a note like "EACH" or "2X" under the datum feature symbol?

I quickly perused the ISO standards I have, I didn't see anything like what ASME has but likely I'm not looking in the right places - here is an example of what I think you are trying to do. Y14.5 utilizes the notation "INDIVIDUALLY" to accomplish this.

 

[TheTick]

Datums in detail views are OK.

 

[Yuyu28]

Sorry I haven't answered before, but thank you for your replies.

chez, I agree that the sliver at the end is too small and probably something like the <CF> modifier should be used. I just wanted to focus the question on the issue of defining a datum in a detail view. From the ISO standards that I have available I also haven't been able to find something like the "6X INDIVIDUALLY" in the figure that you show.

That figure also makes me wonder: isn't it redundant to have the "6X" both next to the datum definition and in the detail view label? Since the small holes are defined 4x times in a 6x times view, that makes 24 of them. If the same applies to the datum D, it could imply that there are 36 datums defined.

I know almost nobody would interpret it this way since it is quite clear what is meant, but it seems inconsistent, at least. Is it maybe that datum definitions are excluded from the multipliers in a view label? That is also why I was wondering whether to put a 2X in the view label OR respective 2X modifiers for all the dimensions defined therein.

 

[chez311]

Yuyu28,

ASME Y14.5-2009 includes verbiage about this:

When a detail view includes a notation of the number of occurrences of that detail view, then the 6X on the INDIVIDUALLY notation may be omitted. The 6X INDIVIDUALLY notation beside the datum feature D symbol indicates that each of the six occurrences of the 79.4-diameter hole acts as a separate datum feature and establishes a separate datum D. The 6X INDIVIDUALLY notation associated with the second segment of the positional tolerances on the 4X 3.6-diameter holes indicates that each pattern of four holes has a tolerance zone framework that is located relative to the specified datums.

The 6X on the "6X INDIVIDUALLY" may be omitted, but it does not have to be and I do not think changes the meaning at all - I think its pretty clear what it means, despite it being slightly repetitive.

That is also why I was wondering whether to put a 2X in the view label OR respective 2X modifiers for all the dimensions defined therein

You could do either or both, going by the above convention - whichever you think communicates your intent best or that you prefer. As a small note for clarity I would probably change it to "2X DETAIL A" if going that route instead of putting "2X" floating on its own line.

Of course this is an ASME convention - I don't know exactly how this plays in the ISO world or if theres a better mechanism to accomplish this, however personally I think the intent is pretty clear and interpretable if you can't find an equivalent supported method.

 

[Yuyu28]

Thank you again, chez, you were very helpful!

 

[greenimi]

chez311,

Per ISO 8015 "The independency principle states that – unless otherwise specified – each GPS specification for a feature or a relation between features shall be fulfilled independently of other requirements in the specification"--copy paste
do you think INDIVIDUALLY note in ISO is needed? Or maybe the default will take care of the design requirements?

Just asking.....I am not an ISO user (just seen some drawings here and there)

 

[chez311]

greenimi,

It doesn't seem to me like it would. The 2X would imply a pattern - I would think some sort of clarification is needed to note that the datum features should be referenced separately/individually.

One could of course eliminate the shorthand method and apply separate datum feature designations A and B to each intended datum feature and reference them separately. For larger patterns this is obviously cumbersome however for the 2X features in the OP this would be a small matter.