Drawing Interpretation

[JacobCheverie]

I am looking at a sphere, Position to datums A and B. A is an I.D. thread pitch diameter (permission granted to use minor) and B is a face. The sphere is drawn at a NONBASIC dimension to the face.

The FCF dictates a planar tolerance zone. How is this so? A diametral zone would be appropriate for Position of sphere to A. Planar zone would be appropriate for sphere to B, but that dim is nonbasic.

I'd assume spherical zone, but what does the print say?

EDIT: To be interpreted per ASME Y14.5-2009

Q.jpg

[Schlag]

I would assume Ø and the 5.536 being basic and moved forward without looking back. If you went back to every engineer and had them fix all the incorrect GD&T we would still be using mostly stone tools.

[JacobCheverie]

If in a diametral zone with the 5.536 to B being basic, then in which axis would the sphere vary from nominal 0 with respect to A?

[Schlag]

Top view of the print , A would be Y 0.0 and Z 0.0 and B will be X 0.0. If a Datum can constrain a DOF it has to. This datum structure doesnt control rotation of any sort but I guess that it is a sphere and on the axis of A, you dont really need to satisfy the Feature control frame but I would have something in the CMM program to fully lock everything in

[Tater]

Think of -A- as a Cylinder and Primary Level Datum

[SingularitY]

Is this section of the print the only part that has dimensions associated to the sphere? Is there any other FCF that uses an AB alignment on the print that would assume simultaneity?
I agree with Schlag (I do not know how to tag people here) that they most likely meant diametrical t/p. In this case since a Sphere is a 3D feature, would it need all 3 axis to find it's position? Since there is no rotation defined, one of the axis about A could rotate until it measures zero and then use the deviation of the other axis along with B distance for calculation. The only other thing I could think of is that the intent of the callout was a T/P only to A just to make sure the sphere is in line with A and the dim to B is actually not basic, but the FCF doesn't state this. Either way, if you check it as it is stated it would either be correct or checking it to a tighter standard than they intended, which a customer should never complain about.

[JacobCheverie]

SingularitY You can tag others using the @ symbol. I agree with what you and Schlag are saying. I assume as a 3D feature that is described by a center point we would locate it in all 3 axes. It would be clever to rotate the coordinate system such that the positional component along one axis is 0, my thought would just be to throw a spherical zone at it so the coordinate system is not "clocked" to make one component zero. You're implying that there are an infinite # of coordinate systems that can be used to measure the sphere position in three dimensions, only one of which will use two dimensions and thus be more practical. I'd assume keep it general and allow any one of the infinite systems and use a spherical zone.

It is really irrelevant, both interpretations will work. The heart of my question was whether the planar zone is acceptable, to which I would say no. Either diametral or, more generally, spherical will work. I think.

[dph51]

The FCF has neither a diametrical or spherical modifier for the tolerance zone.

It is a planar tolerance zone.

[JacobCheverie]

The FCF has neither a diametrical or spherical modifier for the tolerance zone.

It is a planar tolerance zone.

So the Position is equal to 2*X where X = ?

a.) Deviation from sphere center to datum A center along x.
b.) Deviation from sphere center to datum A center along y.
c.) Deviation from sphere center to datum B along z - 5.536.

[JacobCheverie]

SingularitY You're right, ultimately it is up to the drafter/engineer to determine intent. I was just speaking from a GD&T point of view. I'm not trying to have a destructive argument, but you say if it is truly meant to be planar then you are checking where it lies relative to the axis of A. I can argue that if it is truly meant to be planar, we are checking where it lies relative to B. How do you handle a disconnect between interpretations? The standard should not allow for this, and I would like to believe that it doesn't, which would imply that one of the two interpretations for a planar zone would be "more correct". Or that the planar zone is not appropriate.

In any event, you're correct in that I will never pass a bad part by tightening up how I measure it, which is what I will do.

[SingularitY]

JacobCheverie I'll give you my reasoning behind why I think dimensioning would be in relation to A.

-Datum A is the Primary Datum.
-The nominal distance to Datum B is not basic.
-The view with the FCF does not have the dimension called out to B, but implies centerline to A which is assumed basic.I would agree that you shouldn't use views to interpret drawings but sometimes it is useful to try and figure out intent.
-If the planar dimension intended to be in relation to B, there are no other callouts that hold location to A. So, in theory, the sphere could be off greatly in relation to A and no dimension would catch the error.

I believe these reasons are solid enough to assume intent is position to A, not B. I'm sure other people could offer opinions also.

[JacobCheverie]

SingularitY Those are some solid points. I was told by an engineer that this particular customer doesn't box their basic dimensions but I will have to double check on that. Your mode of thinking is most likely correct and it does appear to be relative to the axis of A. I just don't know why they would have B as a secondary datum in this case. It sets a useless origin.