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GD&T Position to a Centerline (wince 😬) Datum


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Hello.  Suppose you were required to measure the position characteristic on this print.  The print uses the centerline as a Datum, which is a no-no.  However, it "appears" the intention is that a line constructed from the center of the two internal holes is Datum A.

Also:

1. There is no diameter symbol in the feature control frame, so no cylindrical tolerance zone is overtly specified.

2. The print does not contain basic dimensions

Question:  Does this position characteristic only control deviation in one axis, which is perpendicular to the Datum A line, or does it control deviation in two axis (presumably in rectangular tolerance zone due to no diameter symbol)?


Position_to_Datum_A_question.thumb.png.420afd7969a49edd12ad8992ed3c84c3.png



Thoughts??

.

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I would think it can only control the single perpendicular axis. There's nowhere along the line that acts as a point to define the horizontal, so you can't define a tolerance zone along that axis in reference to anything.

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That's such bad drawing that it can pop somewhere 🤣

Bad thing is, there is no definition of base A ( does it came from holes, outer radiuses, symmetry of sides ).
Since there is no besic dimensions I would argue there is two possible callouts: concentricity to holes or perpendicularity to face.

And one good point - rectangle tolerance zone is correct.
This drawing would make us send additional questions to customer, or send our corrected version.

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