Datum confusion
Datum confusion
(OP)
Hi,
I have a drawing that uses geometric tolerancing. In many of the GD&T blocks there is what I guess might be referred to as a "compound datum" - datum "C-D." C and D are parallel planes. Particulary confusing to me is a datum point that is called "Intersection of B and C-D at D." Datum B is a plane that is perpedicular to both C and D. What does "C-D" mean when those 2 datums are parallel to eachother and never intersect?
Thanks,
Bill
P.S. I apologize if this is not the appropriate forum.
I have a drawing that uses geometric tolerancing. In many of the GD&T blocks there is what I guess might be referred to as a "compound datum" - datum "C-D." C and D are parallel planes. Particulary confusing to me is a datum point that is called "Intersection of B and C-D at D." Datum B is a plane that is perpedicular to both C and D. What does "C-D" mean when those 2 datums are parallel to eachother and never intersect?
Thanks,
Bill
P.S. I apologize if this is not the appropriate forum.





RE: Datum confusion
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RE: Datum confusion
This question is better posted to the Drafting Standards, GD&T & Tolerance Analysis forum, with an example of your drawing.
The datum specification C-D in your feature control frame indicates that the datum is defined by two features. In the ASME Y14.5M-1994 standard, look for figure 4-20.
RE: Datum confusion
Sounds off to me though, I'd suggest going back to whoever did the drawing and ask for clarification of what they actually want.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Datum confusion
I'm not sure about the second point.
RE: Datum confusion
"Intersection of B and C-D at D" sounds to me to be the same as "Intersection of B and D" since C-D is parallel to D.
RE: Datum confusion
No it is not. See the standards noted above.