Datum feature and Datum feature reference frame.

[TOOLS4FOOLS]

Please see attachment and comment your verified thoughts.

 

[JNieman]

Let's get this out of the way, first...

1.3.13 Datum
datum: a theoretically exact point, axis, line, plane, or
combination thereof derived from the theoretical datum
feature simulator.

1.3.16 Datum Feature
datum feature: a feature that is identified with either a
datum feature symbol or a datum target symbol.

1.3.17 Datum Feature Simulator
datum feature simulator: encompasses two types: theoretical
and physical. See paras. 1.3.17.1 and 1.3.17.2.

1.3.19 Datum, Simulated
datum, simulated: a point, axis, line, or plane (or combination
thereof) coincident with or derived from processing
or inspection equipment, such as the following
simulators: a surface plate, a gage surface, a mandrel, or
mathematical simulation. See para. 4.6.

Now.. back to my response:
"The drafting requirements manual 11th edition:"
I don't know what manual you're talking about.

As with Belanger and others, we mainly speak and cite directly regarding ASME Y14.5-xxxx depending on the one at hand. Your drawing references 2009, so that's the one referenced. Directly.

I personally don't understand your question in the attachment. Sentence fragments are too fragmented for me to conclude your point, and you use somewhat-slang terms that aren't completely familiar to me.

You can find many examples in the 2009 standard which have a FCF with a DRF containing self-referential Datum Feature.

The third datum, as others echoed, is unnecessary, as shown in Fig 4-8 suggested by Belanger. I don't think that's even a debatable point. You mention "truly restricting the six degrees of freedom" but, for emphasis, this is not a requirement. In some cases it may not even change anything by calling it out in the DRF. So I suppose I would not agree that it applies as a "3rd reference" unless you make it so. The wisdom of making it so... that is debatable.

As for 'best practices' - I would start not with "dimensioning to the datum plane" but rather your use of a circular hole pattern, but not calling out the diameter of it, and also lacking basic dimensions to the 12, 3, 6, and 9 o'clock holes. You locate only 4 holes, the way it is dimensioned currently.

 

[TOOLS4FOOLS]

Thank you for all the pointers.