Centerlines needed or not? 3

[kingsboy55]

Hi, I would like to know if there is any definitive method for whether or not centerlines should be shown when using features of size.
The attached file shows a simple angle bracket with two slots in one leg, positioned using implied symmetry to datum A (the length of the bracket) and one slot in the other leg, similarly positioned to A. I sketched red centerlines in to represent the plane of datum A. Some would argue that the red centerline is meaningless and just adds clutter.
The same thing applies to the angle leg with one slot in it, should the centerline be shown through the 2" width of the leg or just locally through the width of the single slot?
We often have animated discussions about this type of stuff, for the record I want to omit the lines in red!

Thanks.

http://www.eng-tips.com/

P. S. As an old guy myself I really enjoyed this thread about centerlines, I can so relate to making holes in paper, chisel points etc...thread1103-248576

 

[looslib]

Checkerhater,
No, and I thought of that after I posted. Centerlines of a feature (hole, slot, boss, etc) are ok to dimension to. The theoretical centerline of the part itself is not.


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

 

[KENAT]

The theoretical centerlineplane of the part itself is not ok to dimension to if established as a datum plane.

Posting guidelines faq731-376

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

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

 

[Belanger]

CH -- why do you say there is no such thing as implied symmetry? Paragraph 1.4(k) of Y14.5 says there is, when something is controlled by a geo tolerance.
Perhaps you mean that there is no such thing as an implied tolerance on symmetrical features?

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

 

[CheckerHater]

Yes, symmetry as measurable control, as in "exactly how symmetrical?"

There is implied zero dimension, implied 90 degrees (both toleranced and basic), there is no implied symmetry.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[Belanger]

CH -- there is indeed implied symmetry. You said so yourself: an implied zero dimension between two or more features that share a common, theoretical center; thus the zero dimension. That's symmetry.

But I see now that you meant a tolerance of symmetry (as in "exactly how symmetrical").

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

 

[ctopher]

Think of it in terms of the person making the part. Is the CL the center of the part or the feature? If it's not clear, leave it off. If the line is needed for some reason, no harm to use it for clarification.
I still see people adding the CL symbol, making it more confusing.

Chris, CSWP
SolidWorks '16
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