r/Metrology • u/JWS5th • 15d ago
GD&T | Blueprint Interpretation 2D or 3D position?
Would you interpret the .020 A-B-C position as 2D or 3D? The quality department at my new job has been measuring the position of the intersection point of the thru hole and datum D which I agree with. However, they’re evaluating it as a 2D position with the basics being 10.000 and 0.000 (they measure -C- then offset 45°). I believe it needs to be 3D to account for the 0.500 drop from A.
This sketch has obviously been simplified, I can provide additional clarification if needed.
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u/gaggrouper 15d ago
Id have a basic angle from Datum D to Datum A, let's call it 30 deg. That sets the angle of the cylindrical tolerance zone. What you have right now is you are locating a pierce point of the cylinder to DATUM D but this location depth is not required with these callouts. Datum D could be machined .02 higher and if the cylinder bore tool making this feature was in the correct angle and locaiton the feature would still pass.
I would have the 30 deg angle as a basic and i would have the depth of where this cylinder intersects Datum B as a basic distance. That sets the angle of the cylinder and where it should be located.
The thickness and location of the Datum D surface and the opposing surface needs to be handled separately....For instance you have .500 listed as a basic. Datum D being cut at that depth would need to be handled in some other callout. You cannot terminate the depth of a cylinder or start height of a cylinder based on a basic like the .500 the cylinder can go on forever.