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Alteon

GD&T: When did companies start thinking that Total Runout could lack a datum? (self.mechanical_engineering)

submitted 5 months ago by Alteon to c/mechanical_engineering

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I've been dealing with this for months. I've received yet another drawing from a company calling "Diameters on a common axis/center to be 0.XX" TIR U.O.I. "

Total Runout requires a Datum. Your "common axis" is not a datum and can not referenced. It's driving me mad. Like, where did everyone get this notion that it's acceptable? It'd be one thing if it was just one or two drawings, but I'm into the dozens at this point. It's getting to the point that I'm starting to question if I'm either the one in the wrong or everyone has some sort of mass psychosis.

Am I in the wrong here?

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[–] CorneliusTalmadge 1 points 5 months ago (1 children)

If I am thinking of this right, you can make the datum a common axis but you have to define which feature creates the common axis.

[–] Alteon 2 points 5 months ago

According to ASME Y14.5, I believe you are correct. You can establish a central axis, but you still have to establish WHICH surface dictates that axis. So I'm entirely unsure where everyone is getting the Note Call-out from.

Only thing I can think of is a bigger company like Boeing or Airbus has been calling out something similar on a drawing and people are just going "oooooh, that's an acceptable thing". It started somewhere....