Can the same Datum be considered by multiple axis (non-coaxial) elements? 1

[Fernando258]

Hello everyone, we have a drawing from one of our customers of a Pipe Assembly (exhast components).
The assembly have 4 straight sections and 3 arc (bended) sections, this is a multiple axis bended pipe assembly. And in one of the straight sections (lets call it 'section #3') we have this dimension: '4X (∅88.9)' and attached to it has a Datum flag.
I ask the customer for clarification since there is a FCF of Concentricity in another component that joins the 2 pipes that make up the assembly, since these elements are not aligned (are not coaxial) to the straight section that has the Datum flag on it (lets call 'section #2' where FCF is attached). And the customer answer was that 'the Datum consists of the four straight pipe segment', for the moment I just take this as 'GO' to consider the straight section #2 as the reference Datum to report the concentricity, but is the argument that our customer says even valid? Could a multiple non-coaxial axis be taken as the same datum (together or individually)? (Just to clarify, 'INDIVIDUALLY' note was not added to the mentioned datum).

In the time that I've been working here I have seen some 'strange' GD&T practices from our customers but haven't seen something like this before.

 

[Ryan6338]

Firstly, concentricity was removed as of ASME Y14.5-2018 because it's difficult to use and interpret correctly; other methods can achieve the same outcome with more clarity. In older versions of the standard, it could only be applied to a datum axis or centre point. I think creating a common datum from the 4 straight sections is allowed but it would create a common complex datum, which concentricity couldn't be applied to.

Ryan.

 

[3DDave]

This is why inspection needs to be part of the bid process. As in - when drawings come in and no one has an idea what it means, don't bid on the item. Or bid $1 Billion. If they ask why so much, explain that is to cover arguing over what is acceptable or not.