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Can we mention a datum twice in the same drawing?

Can we mention a datum twice in the same drawing?

(OP)
HI,

I came across a drawing which has a datum specified with a geometric tolerance and also on a surface (in a different view).
I wanted to understand if this is the standard practice.

Regards,
VJ

RE: Can we mention a datum twice in the same drawing?

Can you provide a sketch?

Certified Sr. GD&T Professional

RE: Can we mention a datum twice in the same drawing?

Vikas Jangre:

This is acceptable. You can repeat the datum symbol with the same letter as many times as you want, as long as it is applied to the same feature (in another view/section). Assuming a multi-sheet drawing, I recommend only adding it to sheets that depict a feature control frames (FCF) that have the letter in them (define a relationship with controlled feature and the datum feature).

Certified Sr. GD&T Professional

RE: Can we mention a datum twice in the same drawing?

1994 & 2009 3.3.2 - ".....Where the same datum feature symbol is repeated to identify the same feature in other locations of the drawing, it need not be identified as reference."

RE: Can we mention a datum twice in the same drawing?

(OP)
Thanks Andrew and Mkcski.

One other question regarding to the pic posted is:
I got to know that datum mentioned on the left view is on the surface whereas datum mentioned on the right applies to axis.
If this is the case, then simultaneous representation of datum will not work. Am I right?

RE: Can we mention a datum twice in the same drawing?

VJ1988

They both are interpreted the same and define the axis as the datum. This is a drafting issue. There are several ways to assign datum symbols to features of size. I suggest referring to Figure 3-4 and Figure 4-3 (d) in Y14.5-2009

Certified Sr. GD&T Professional

RE: Can we mention a datum twice in the same drawing?

Both instances of calling out the hole as datum feature "B" are in accordance with the standard and both mean/yield the same thing.

2009 4.3 (d) - "a cylindrical datum feature establishes a datum feature simulator that creates a datum axis (line) and constrains four degrees of freedom (two translations and two rotations)."

RE: Can we mention a datum twice in the same drawing?

(OP)
Thanks a lot mkcski & Andrew TT.
I have more further questions on this however, I will ask in a separate thread.

RE: Can we mention a datum twice in the same drawing?

Maybe you could, but I see no reason to.

Quote:

I got to know that datum mentioned on the left view is on the surface whereas datum mentioned on the right applies to axis.
No. Both are the same, which is the surface. There is no such thing as an "axis datum", only an axis derived from a feature.

RE: Can we mention a datum twice in the same drawing?

Quote (AndrewTT)

2009 4.3 (d) - "a cylindrical datum feature establishes a datum feature simulator that creates a datum axis (line) and constrains four degrees of freedom (two translations and two rotations)."

Just an observation: The number of degrees of freedom (DOF) stated is only for a Primary Datum Feature. The number of DOF decreases as the datum moves from primary to secondary and tertiary.

Certified Sr. GD&T Professional

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