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Weird GD&T Callout


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I have a drawing calling out a (bi-lateral) position of a curved 3d surface. similar to a bowl.

I get these types of parts all the time and normally this surface is called out as surface profile.

The surface extracts as a torus. I'm baffled. Any ideas? I think the drawing is wrong.

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I don't know why Surface Profile would not give all the necessary information; it's more informative than position.  As to whether or not the drawing is correct, I guess I can't say without looking at it.

Does it specify "bilateral"?  Position always extends the zone to all sides of nominal.  There's no provision for a unilateral or unequal zone in position; at least not in ASME.  If it says bilateral I'd go with surface profile and never look back.  It literally controls the location of every point.  Good luck.

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Turns out that the geometry extracts as a torus. and does produce the correct nominal in Z which will work in true (bi-lateral) position.

I've just never seen a surface like this being called out with a position tolerance.

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