GD&T refresh.

[AuRules]

3456.jpg

Once again debating at work about True Position, and want to see if I'm correct again. The FCF @ MMC above is Datum A so I told them what its asking was the centerline of the hole to be perpendicular to the plane it's drilled thru. Thanks for any response. I need a raise.

[NinjaBadger]

I think it's garbage.

A single hole with no datums specified doesn't make any seance.

I'd take that Label to mean that the hole is Datum A, If the call out was to Datum A it would be in the FCF to the right of the tolerance and the (M).

[AuRules]

I think it's garbage.

A single hole with no datums specified doesn't make any seance.

I'd take that Label to mean that the hole is Datum A, If the call out was to Datum A it would be in the FCF to the right of the tolerance and the (M).

Yes that's always been a wacky call out it's datum A and the FCF is to itself. So I always took as Perpendicularity. But "HEY" I could be wrong.

[Peter Fuller]

I used to see this very frequently in medical devices, and I agree it's garbage. But it was usually the engineer trying to specify a through hole or a screw hole be perpendicular to a datum/surface. My usual course of action was to get the responsible engineer for the print to define it for me in writing.

[RIDER]

I agree with NinjaBadger that the hole is Datum A. The 90° angle of the whole is indeed implied. The location of the hole should be defined by the basic dimensions that are called out on the print. So effectively, the engineer has made whatever the surface that the 1.150 basic dimension is pointing to a "datum" for the hole location.

[DungT]

Per older ANSI Y14.5 standard, an unspecified datum whose influence on the application is implied by the basic dimension arrangement...it's called implied datum.

[NinjaBadger]

Interesting... I'l have to read up on that...

[Trevor McLaughlin]

I think a committee of engineering professionals should get together and make up some kind of a "GD&T Standard" so that these types of interpretation problems don't come up.

[Ego Murphy]

I think a committee of engineering professionals should get together and make up some kind of a "GD&T Standard" so that these types of interpretation problems don't come up.

Yes, but then they would keep releasing different versions every decade or so and confuse everyone.

[AuRules]

Been reading, one of guys said if you had cad it means you can compare it back to the cad model which then I was thrown for a loop.

[Quality ish]

I've always taken a hole in relation to the plane it goes through is an implied perpendicularity.

Say you've got TP to A,B, &C, where A is the plane it's going through (Z), B constrains the X axis on the left side of the part, and C constrains the Y axis at the bottom of the part. You're really only checking the location of the hole to X and Y (B and C), but where does the A plane come in? An implied perpendicularity.

This mess? I've never seen a TP callout in the FCF along side diameter callout like this. I'd be on the phone with the engineer.