"Partial" datum reference frame.

[Burunduk]

ASME Y14.41 Section 3 para. 3.11 defines a Datum System as "a partial or complete datum reference frame".

A search in Y14.5-2018 for a "partial" DRF generates no results. Rather, a Datum Reference Frame is three perpendicular planes by definition.

Every feature control frame that includes one or more datum references is associated with a Datum Reference Frame (disagreements?).
So the way I see it, considering the Y14.5 definition of a Datum Reference Frame (para. 3.19) even when one datum is referenced which is associated for example with a planar true geometric counterpart establishing a single datum plane and nothing else, the datum plane is still part of a 3-planes DRF (but only this one plane is used for constraining DOF). Therefore for me a "partial DRF" seems like soneone's misunderstanding of the definitions in ASME Y14.5.

What are your thoughts on this?

 

[greenimi]

I think datum system terminology is part of ISO system (and not ASME's)
Maybe ISO5459:2011 could be another standard to look for....

Maybe "datum system" word in ASME is just copy-paste from equivalent ISO16792 Technical product documentation — Digital product definition data practices standard

3.1.2
datum system
set of two or more situation features established in a specific order from two or more datum features
Note 1 to entry: To define a datum system, it is necessary to consider the collection surface created by the
considered datum features. The invariance class of a collection surface can be complex, prismatic, helical,
cylindrical, revolute, planar, or spherical (see ISO 5459:2011, Table B.1).
[SOURCE: ISO 5459:2011, 3.10]

 

[Burunduk]

Maybe "datum system" word in ASME is just copy-paste from equivalent ISO16792 Technical product documentation — Digital product definition data practices standard

"Datum system" defined as "a partial or complete datum reference frame" appears first in the very first revisiin, dated 2003, of ASME Y14.41. ISO16792 didn't appear until three years later, so it is more likely that ISO copy-pasted definitions from ASME not the other way around. With that said, the quote from ISO5459 you provided does suggest similarity between the concepts. Could the ASME Y14.41 "Datum System" be an attempt for uniformity with ISO5459 at the expense of compatibility with ASME Y14.5 which is supposed to lay its foundation?

 

[3DDave]

Burunduk,

You are probably wrong on the order of copy-paste as there are shared membership on committees and privately shared drafts that the public doesn't see. It is very likely copied from an early members-only draft. It takes about 10 years to get a standard processed and they are willing to make large changes to gain points with the other groups - witness the use of the toilet plunger symbol for datum feature identification.

Only committee members could authoritatively comment on "Could the ASME Y14.41 "Datum System" be an attempt " and they never will. Great question, but it's otherwise one of about 100,000 similar questions about questionable content that will also never be answered.

 

[CheckerHater]

Could it be they meant "partially constrained datum reference frame", because in some cases third datum cannot be meaningfully applied?

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