Datum C (2x)

[[An...]]

See attached.

(E.o.T.)

Pic_7-27.pdf

[[An...]]

In my opinion, I would define an oversight here.
I have never seen several references with the same label.

[[Cl...]]

Possibly the engineer meant that the symmetry of the two surface is the Datum?

[[Aa...]]

This is from the standard.
In the standard, the lower one says Surface D.
Andreas, where did you find one that says C?

[[Aa...]]

Don't confuse those surface labels with datum feature labels.

[[Cl...]]

In my defense, they are labeled datums in his post. So what are those two surfaces?
Is there a note we don't see that explains them?

[[Aa...]]

7.4.3:
"Where design permits, different positional tolerances may be specified for the extremities of long holes; this establishes a conical rather than a cylindrical tolerance zone. See Fig. 7-27."
Those surfaces establish the extremities where those different tolerances apply.

[[Cl...]]

So, how did the original attachment come to have the title "Datum C"
(2x) and show both surfaces as C?Also, what is his question?

[[Aa...]]

Your guess is as good as mine.

[[Ja...]]

May be this tolerance is used, to allow drill wandering.

[[An...]]

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Interesting,
seems to be a kind of "Translation-Error".

Bild_3.JPG

[[An...]]

now it makes sense.

[[Jo...]]

What am I missing? The two surfaces are C and D even in the German version. Does fläche mean datum?

[[Aa...]]

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That lower frame has them both labeled as C. My guess is it means "surface", since that's how it's labeled in the English.