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Datum precidence


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Datum feature simulater of datum B might not constrain rotational degrees of freedom, it depends upon on how the part function.
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As I see it:
A.B.C would have origins at A and B and planar from C
A.C.B would have origins at A,B, and C and planar from C

Tolerances ideally should reflect the function of the datum surfaces, but we don't have this information
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This is simply a hand held instrument. The finished product has 3 spheres attached to (D1, D2, D3).
These spheres are picked up by a camera system used by a robot for targeting were to cut or drill.
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Designers need to start explaining what they actually want.

Maybe something like attached would help with this. Just spell it out.
659_59df65575615a87fb4f08af268ab639a.png
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Either A|B|C or A|C|B are legitimate design decisions. Without information on the design intent, it is hard to recommend one over the other.

Personally, from a functional point of view, I would make B the pattern of holes, and call out a profile to A|B for the tip of "C". That probably best represents the described design intent.
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Yep ISO 5459. Taken from book from 2019 Geometric tolerances by ISO GPS Author Ing. Karel Petr, Ph.D.
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Y14.5-2009 has one too - the "datum translation symbol" AFAIK, it is the same effect. It is a sideways triangle. 1132_cb71d1738cca0c92c48d1f570e0f7991.png
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