How do I interpret this call out?

[Gregg369]

How do I interpret this call out?

 

[greenimi]

Location and/or orientation of the star shape figure is within .0025 (upper value)
Form is refined to .0008 (lower value) and is unequal distributed. It is allowed to be only bigger (in the direction of reducing material). Probably to avoid interference with the socket key tool

 

[Burunduk]

It was probably intended to apply the profile of a surface tolerance all around the socket, although someone forgot to add the all around symbol to the leader.

The surface shall be located and oriented within .0025 relative to datum feature A (the screw shaft?).

The form and size of the socket shall be within .0008, but the tolerance zone is only in the direction that reduces material - which means the socket can only be bigger than its basically defined profile.

 

[SeasonLee]

Would you please advise what the datum feature A is.

Season

 

[Gregg369]

Thank you all, Datum -A- was the head of the screw, where the hexalobe is centered.

 

[greenimi]

I agree with Burunduk. Small circle to represent profile all around is missing.
Most likely an inadvertent error.
I assumed was there to not create more diversion about the OP’s question and I answered directly.

 

[SeasonLee]

The symbol of circle U indicates a unilateral or unequally disposed profile tolerance, and the value(.0000) followed circle U indicates the offset value to apply to the MMC of the closed socket profile(increase material)), but in this case it means all tolerance apply to the LMC of the closed socket profile(reduce material), and it will make the closed socket bigger than the true profile as Burunduk mentioned.

Actually, your picture had shown the socket profile will be bigger, please note on the picture attached below.

The upper segment FCF callout with datum feature A which means it will control the size, location, orientation and form of the closed socket, while the lower segment FCF callout without any datum reference which means it will control the size and form only.

Season

 

[supergee]

Hello,

Pardon my English... not my native language.

While I would personnaly always add the all around symbol, per Y14.5 2009 it is not mandatory when the extent of the surface is clear.

As for the way to interpret it, this is what I tell my students.

for the upper part : the pointed profile must be withing two curves that follow the profile, separated by 0.0025 and equally spaced around the perfect profile while maintaining the orientation and location with datum A

For the lower part : the pointed profile must be withing two curves that follow the profile, separated by 0.0008 unequally spaced around the perfect profile, .0000 on the side of the maximum material, the rest on the side of minimum material, regardless of any orientation.

Gee

 

[Burunduk]

While I would personnaly always add the all around symbol, per Y14.5 2009 it is not mandatory when the extent of the surface is clear.

By default any leader directed geometric tolerance applies only to the surface the leader points to. So if you have a closed shape comprised of several surfaces such as several radii tangent to each other, and the leader from the feature control frame points to one of them - it will control just that radius and not the entire closed shape, unless the all around symbol is used. The all around symbol groups the different features into one pattern. It's also similar with the use of "between" symbol - this one also shouldn't be skipped when applicable.

 

[Belanger]

I agree with Burunduk -- even if the 2009 standard says that all around isn't needed if extent of the surface is clear, how do we define what "clear" means?

Most GD&T folks will say that if there is no "between" or "all-around" indication, then the profile tolerance only applies to the feature being pointed to (in this case, the radius). As soon as that radius transitions to another radius or a flat, then the profile stops.
Of course, for this example that would make no sense, so we can reasonably surmise that they just forgot to add the all-around symbol.


John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems