Symmetry Challenge

[Burunduk]

Can you spot the mistakes in both the Geotol explanation and in the means this literal explanation from ASME Y14.5-2009 fig. 7-66?

 

[ctopher]

The shape would be like a Parallelogram. The last image looks wrong.

 

[Garland23]

For the ASME image, they failed to show the dots in the right-side view, and they mistakenly used the term RFS for the datum when it should have been RMB.
Still studying the first one....

 

[Burunduk]

For the ASME image, they failed to show the dots in the right-side view, and they mistakenly used the term RFS for the datum when it should have been RMB.
Still studying the first one....

You nailed it for the ASME figure

 

[pmarc]

For the GeoTol explanation, Symmetry is not a derived median plane control.

 

[3DDave]

I like when a document that costs hundreds of dollars is afforded the care and attention to detail, even in the smallest areas like capitalization or explanation. Can't expect them to have established a style guide while telling everyone else how to do things.

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Does it matter? ASME made clear that symmetry was just too difficult to use and position was a perfect substitute for every possible situation that symmetry could be put to. That isn't true, but they are the experts to be obeyed in all matters.

 

[Burunduk]

For the GeoTol explanation, Symmetry is not a derived median plane control.

Yes, that's it

For the derived median plane, the "center points" are obtained from distances between surface points normal to the unrelated actual mating envelope.

On the other hand for symmetry, the "median points" are obtained from distances between surface points normal to the datum plane.

Note how the "derived median plane" uses the term "center points" while symmetry uses "median points"

 

[greenimi]

Digging....I found this thread started by pmarc

What is a difference between Center Point and Median Point? - Drafting Standards, GD&T & Tolerance Analysis

These two terms show up in two different definitions throughout Y14.5. Center Point is used in Derived Median Line definition (1.3.31), while Median Point is something that Concentricity deals with (7.6.4). How would you describe a difference between them? Is there any? Thanks a lot for any input.

www.eng-tips.com

I think ...I might be wrong however....could be somehow related

 

[pmarc]

It is related and I agree with Burunduk that the terminology could be better.