Old article --rule#1 expanded to irregular features of size...not sure I agree

[gabimo]

Authors:
Al Neumann
Scott Neumann
Technical Consultants Inc.

New ASME Y14.5 - 2009 Standards for GD&T article.
Machine Design Magazine


The use of direct-tolerancing methods, limit dimensioning, and plus-minus tolerancing are used to control the size of features only. The limits of size, Rule #1, has been expanded to include irregular features of size. Irregular features of size are features other than a sphere, cylinder, or two parallel planes.

http://www.machinedesign.com/basics-design/new-asme-y145-2009-standards-gdt

 

[JNieman]

/edit/ sorry, I missed the "not sure I agree" part of the title. Post rewritten /edit/

What specifically do you disagree with?

Section 1.3.32.2 does a clear job explaining the definition of an IFoS.

2.7.1 seems to be clear enough to me, that it may include irregular features of size, as well as regular. If not a, b, or c, then d is quite open to allow for IFoS to have form control:

(d) In cases where a geometric tolerance is specified
to apply at LMC, perfect form at LMC is required. See
para. 7.3.5.

 

[Belanger]

Rule #1 does not apply to irregular features of size. (JNieman -- see the first part of paragraph 2.7.1. That sets the main condition that it's only for a regular FOS.)

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

 

[JNieman]

Ah, yes, that narrows the context of the following statements, I misinterpreted. Thanks for the clarification.

 

[greenimi]

I guess the text should have been:

The limits of size, Rule #1, has been expanded to include irregular features of size. Irregular features of size are features other than a sphere, cylinder, or two parallel planes.

Do you guys agree with my assessment?

 

[mkcski]

Yes. The irregular FOS "concept" is primary associated with to establishing datums. So an IFOS they can have a RMB. LMB or MMB boundary, but the size cannot control form of the irregular feature per Rule #1.

Certified Sr. GD&T Professional

 

[greenimi]

Wouldn’t be awkward to disagree with someone from the committee who helped writing the standard?

Or these articles are written with so much speed and lack of attention (therefore careless for details)…….