Positional tolerancing and implied symmetry 1

[PobbeS]

Often I have patterns of holes or other features symmetrically located on a part. My question is if the symmetry is implied according figure B in the attached picture or is is neccessary to dimension each of the holes separately to the symmetry plane as in figure A?

 

[drawoh]

redlerm,

Implied symmetry means that the nominal state of the part is symmetric about some feature. The geometry of the part is controlled by ± tolerances, positional FCFs and profile FCFs. Symmetry is not explicitly controlled. A significant asymmetric state would violate one or more of the tolerances noted above.

You may apply sloppy ± tolerances, positional FCFs and profile FCFs, and then apply an accurate symmetry FCF. Now, your otherwise sloppy part is specified to be symmetric about the datum feature(s).

I have no idea of why you would want to do this. If I wanted a rotating component balanced, I would specify the maximum radial force, and the rotation speed.

JHG

 

[pmarc]

redlerm,

If I understand you correctly, fig. 1-33 from Y14.5M-1994 or fig. 1-35 from Y14.5-2009 may help you.
However, if any features violate part's nominal symmetry, I wouldn't recommend this method.

 

[KENAT]

Belanger, what implications does your suggestion of using "CL SYM note" have on interpretation?

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[Belanger]

It means the exact same thing as Fig. 1-35 that you reference (2009): the given picture and dimensions are replicated/mirrored around a center line. (There is the separate discussion about tolerancing about the center line; i.e., what is the true datum. But Redlerm seemed to just be asking a drafting question.)

But I do like the idea of using symbology over notes, so I'll change my recommendation to that given in 1-35.

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