Is it valid to have a Free-State symbol here? 1

[SeasonLee]

Please ref to the figure below, two questions need help:

1. Is it valid to have a Free-State symbol within the flatness FCF? Since the restraint note on the drawing will override the Free-State default condition, so I will say No, am I right?
2. What's the meaning of the 2nd segment flatness callout?

Thank you for the help

Season

 

[Dean Watts]

Burunduk,

CF works for a general feature just as it does for a FoS. Defining two nominally coaxial cylindrical surfaces as one feature by using CF means their coaxiality will be controlled, just due to the single perfect form boundary at one size limit, and all local sizes being within limits, imposed by a size tolerance. Defining two nominally coplanar planar surfaces as one feature by using CF means their coplanarity will be controlled, just due to the single two-parallel-plane tolerance zone imposed by a flatness or orientation tolerance.

It seems that you will never like it. That's fine. It still works fine for those who do like it.

Dean

http://www.validate-3d.com

 

[Burunduk]

Dean,
I agree with the point, and pmarc noted it too - that the effect of CF modifier applied on a FOS can be achieved by applying mutual position control specified with zero tolerance at MMC on the pattern of coaxial same-size diameters or symmetrically aligned same-size widths.

That makes the entire concept somewhat redundant, but the FOS application of CF does not create conflict with any fundamental principles - such as what type of tolerances are allowed to control the mutual location of features. It is also more efficient and elegantly independent - it does something meaningful even when not supplemented by any feature control frames (the common rule #1 conformance evaluation for the different portions of the feature).

You are right, I will never like the idea of a tool used in a way that may blur important distinctions and lead to associating flatness or orientation with coplanarity.

 

[SeasonLee]

As pmarc noted that it is really interesting to turn the Free State question into a CF discussion, thanks for all you guys' comments, I would like to share the author's comment from his textbook---Fundamentals of Geometric Dimensioning and Tolerancing 3rd edition based on Y14.5-2009.

Season

 

[pmarc]

This summarizes perfectly the clarity of CF definition and applicability in 2009.

 

[greenimi]

As pmarc noted that it is really interesting to turn the Free State question into a CF discussion

Season,
Sorry about that. My apologies. I am guilty somehow for that, as I have tendency to stir the pot.

 

[SeasonLee]

@greenimi
Its not necessary to say that, I always learned something new from this forum and I am glad to know different view points from all of you.

Season