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Tertiary datum on Drawing

Tertiary datum on Drawing

RE: Tertiary datum on Drawing

Ask yourself: will it become different part if rotated?

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

RE: Tertiary datum on Drawing

CheckerHater and KENAT,

Actually, no! There is no problem rotating the part. This ceases to be true if you add any features not concentric with the hole.

--
JHG

RE: Tertiary datum on Drawing

Still, I would apply the third, clocking datum.

--
JHG

RE: Tertiary datum on Drawing

Since the profile tolerance goes all around, there really is no option for a tertiary datum. The rotation is actually controlled by the profile tolerance itself.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: Tertiary datum on Drawing

Quote (Belanger)

The rotation is actually controlled by the profile tolerance itself

Rotation implies some sort of an angle. Which angle in this case is controlled by Profile tolerance?

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

RE: Tertiary datum on Drawing

Quote (drawoh)

Still, I would apply the third, clocking datum.

What for? Implied 90 deg. angles and Sim. requirements are keeping the pieces together.

See ASME 14.5-2009 Fig. 4-39

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

RE: Tertiary datum on Drawing

Quote:

Rotation implies some sort of an angle. Which angle in this case is controlled by Profile tolerance?
All four corner angles!

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: Tertiary datum on Drawing

I am OK with corners. OP's drawing is actually pretty tight. The only thing you can rotate around datum B is the drawing view itself.

Which brings interesting afterthought: there is no such thing like implied horizontal (or vertical) line. We take for granted that certain edges of the part are (arbitrarily) made parallel to the edges of drawing sheet, but it is merely a matter of convenience.

What if you are trying to make a sketch on a piece of paper that is not rectangular at all? Could anyone reference the rule that makes the view on the right of enclosed picture "illegal"? No, seriously.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

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