GD&T Centering
GD&T Centering
(OP)
I have two slots on a plate, and want the centerlines of the two slots to be within a specified tolerance (they are nominall aligned). How would I put this on the print?
The sizes of the slots are not controlled and not important, as long as the centers are aligned.
The sizes of the slots are not controlled and not important, as long as the centers are aligned.





RE: GD&T Centering
It's not often that someone really cares about the center (though folks often care they do), usually it's where the edges are that matter and so that is the more common case an application of GD&T.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: GD&T Centering
I'm trying to follow ASME Y12.5M '94
The only idea i have is to define a datum as the center of the first slot, define the second slot centerline, and then put a positional feature contorl frame on the second one relative to the first datum.
RE: GD&T Centering
Although keep in mind that the datum and the position tolerance are derived from the "actual mating envelope" of the two slots (i.e., derived from just the high points).
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: GD&T Centering
RE: GD&T Centering
Notice the datum symbol is in line with the dimension arrow for the width. This means that the true datum is the center of the block, not the one wall on the right.
In GD&T a datum is often a center line/plane, but the symbol itself must be identified with the physical feature that the center is derived from. I know this might not be intuitive, but them's the rules!
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: GD&T Centering
The ways to align your slots may actually differ depending on overall design of your part (some other features, the way you want them to be controlled; what is called “design intent”)
RE: GD&T Centering
RE: GD&T Centering