Spherical tolerance zone question

[JacobCheverie]

I have been with this latest company for just over a year. I have yet to see an "S" preceding Ø on a Position FCF. Many of the features that they are positioning are spherical. Am I being too hard on inspection by forcing parts to pass their tolerance in a spherical zone? It doesn't make sense to me why you would only control 2 components of position on something like a sphere.

[dph51]

A spherical tolerance zone controls x,y & z.

[JacobCheverie]

I understand that. What I said was there will be a Position callout on a sphere, but the FCF only shows Ø, not SØ. Do I assume they want spherical tolerance zone or a diametrical tolerance zone as the print suggests? If diametrical, which two dimensions are being controlled and what is the justification?

[UKCMM]

Without seeing the print or a sketch it is impossible to say if a spherical zone is needed.

At present we are running a part with a spherical end and all that is called out and needed for the function of the part
is a 2d zone the 3rd axis is open tolerance. Going to a spherical zone would serve no functional purpose and only add to
production cost and unnecessary scrap.

[JacobCheverie]

UKCMM I have attached a sketch. The Position with the arrow is the one in question. Should the tolerance zone be spherical or diametrical as drawn?

sketch.jpg

[Mike Ruff]

X,Y, and Z are controlled by your DRF, so I would expect PC-DMIS to calculate it as spherical tolerance zone

[MikeD6]

No. You can control its size and form with a spherical diameter and tolerance above the FCF, but not its orientation or location because you don't all 6 DOF locked up yet. All you have is a plane and a sphere to reference off of so far.

[Mike Ruff]

Datum A is a cylinder, so only rotation about the axis of datum A is unconstrained, which has no effect on a sphere. Orientation of a sphere does not matter

[MikeD6]

Is a Datum A a cylinder, or the flat side of the part? I can't tell. And yes, orientation doesn't matter, I was thinking location. It depends on whether A is cylinder or a plane whether you can even have a spherical tolerance zone.

[JacobCheverie]

Mike Ruff is correct, -A- is a cylinder. I can determine -D- to -B- along X, and -D- to -A- along Y and Z, thus implying a spherical zone. But our prints have never shown spherical zones, only diametrical. I am beginning to believe that they just don't understand when/why to put SØ. I don't want to make that jump to conclusions myself though. What is the justification, can may must rule?

[Mike Ruff]

Do you get different results in PC-DMIS with or without the "S"?

[Peter Fuller]

Mike Ruff is correct, -A- is a cylinder. I can determine -D- to -B- along X, and -D- to -A- along Y and Z, thus implying a spherical zone. But our prints have never shown spherical zones, only diametrical. I am beginning to believe that they just don't understand when/why to put SØ. I don't want to make that jump to conclusions myself though. What is the justification, can may must rule?

The way the leader line and feature identifier are drawn, I believe you are correct in assuming that they're implying a spherical zone. I personally try to make a habit out of not dimensioning to an implied or assumed guess. Contact the engineer in charge of that print and get a determination in writing in my opinion.

[JacobCheverie]

Thanks Peter, I'll get in touch with the engineers when I run into the issue.