Writing Datum After A Basic Dimension

[K_Ho]

Hey guys,

I having an issue determining the meaning of a basic dimension with the word Datum written after it.
Can you guys please clarify. I only have a light knowledge of GD&T.
I attached an image of two examples they are showing up.

Thanks.

 

[CheckerHater]

Dimensions on your drawings are NOT basic.
Datum B doesn't seem to be identified correctly.
Drawing is most likely created by someone who's knowledge of GD&T is even lighter than yours, so don't worry. It's essentially meaningless.

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

 

[ewh]

Agree with CH... does not add any value and should be omitted for a concise drawing.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[Belanger]

Perhaps they meant for the given dimension to be measured from the datum side. If so, the proper way to do that would be to use the dimension origin symbol (a little circle that could replace one of the arrowheads on the dimension line).

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

 

[TheTick]

Whatever it is, it ain't kosher. Looks like someone just making things up as they go.

 

[semiond]

Source

If they mean a "basic dimension" why use the term "datum"?
Not sure what this means, and it doesn't seem to be in line with the terminology of ASME standards, but perhaps this is what they meant?
Is anyone familiar with this???

 

[Tmoose]

"I only have a light knowledge of ..... "

Nice phrase, and very descriptive.
I'd like to use it in the future, if I may.

thanks,

Dan T

 

[3DDave]

The book is by an associate professor written for Pearson Education. That publisher is not a reliable source of materials. It's good for Papier-mâché.

 

[CheckerHater]

It's good for Papier-mâché

If it's heavy enough, then maybe for presse-papiers.


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

 

[semiond]

I found this page on a google books preview when looking for what the term "datum dimension" might mean. I don't know anything about the publisher or it's reputation, but i'd like to think that there are no engineering "professors" out there making things up completely out of the blue just to sell books. Maybe this is some outdated/local terminology? This might explain why the OP of this thread also encountered this.

 

[3DDave]

semiond, I'd like to think so too, but the reality is that professors will make up things to get paid, and the most likely source of garbage is the publication-to-education pipeline. Read up on Richard Feynman's experience in evaluating school textbooks. It's possible that someone took a course using that book and made the drawing - it's not outdated if it didn't exist before. And plenty of consultants make things up out of the blue to justify their position. If what they did could be learned from other material, why would anyone need their contribution?

 

[semiond]

3DDave, what you say is probably (but sadly) true.
And the problem with a field of knowledge like GD&T is that there are more than one international standards dealing with the same concepts, having the same terms/symbols interpreted differently here and there, and in addition to that even when one is basing his practice on one particualr standrd only, the terms and concepts within that same standard are often not fully defined or inconsistent (this is at least what i've learned since starting to read and participate in this forum). I think this situation leaves a lot of holes through which all those charlatan "experts" you talk about can crowl in, recognizing opportunities to make profits out of all the ambiguity and confusion.