With editorial contributions from Evan Janeshewski and Ron Grube Multi Metrics & SmartGD&T
In March 2009 the ASME has released a new Y14.5 standard, the first since 1994, and there is much in it of great interest and benefit. In order to help potential users decide whether or not to adopt it, we attemptto cast some light on its most important novelties. To set the stage, we start with a definition of GD&T as a whole, in order to be sure we are all on the same page. Next we ask why a new standard might be interesting. Finally, we provide a brief overview of the contents of this evaluation before we go into detail. What is GD&T? GD&T is a symbolic language with which to research, refine andfinally encode the functions of each feature of a machine part by specifying permissible limits of imperfection to guarantee its operation, assemblability, manufacturability and inspectability. Whereas CAD is dedicated to communicating the geometry of a part, GD&T is dedicated to communicating its functional requirements. . Why do we need a “new” Standard? Standards always represent our bestunderstanding of a topic at the time they are released. In most cases we keep learning as we go, and in the case of GD&T we have learned a lot since 1994. The many changes contained in Y14.5 2009 represent very useful advances and clarifications which will further empower the designer to fully and reliably express the desired functions of machine parts. In particular, they will result in significant benefitsfor Tolerance Stack-Up Analysis, for clear communication of manufacturing objectives, and for empowering coordinate metrology software. As we might suspect, however, not everything needing attention can be addressed in a new standard, and there are a few disappointments which also need to be logged. Overview of the Most Important Changes: The most important changes in the 2009 Standard arepresented in three groups. Click on any topic to go there directly and then hit the “Return” button to come back, or simply scroll through the entire article. In order to fully comprehend much of this overview, it is imperative to have a copy of the 2009 Standard at hand to study the figures referenced in the explanations, which limited space does not permit us to duplicate here. 2. New and refinedConcept Definitions 2a. 2b. 2c. 2d. 2e. 2f. 3. Material Condition Modifiers Geometric Tolerance Value Modifier Details Material Boundary Modifier Details Datum Feature Simulators Datums Actual Mating Envelopes
New and refined Tools 3a. Datum (Feature Simulator) Translation Modifier: ► 3b. Degrees of Constraint Modifiers: [u,v,w,x,y,z] 3c. Explicit Datum Feature Simulator Size and LocationModifiers: [BSC] / [Ø15] 1 Copyright © by Multi Metrics, Inc. Menlo Park, CA 2009 - All Rights Reserved
SmartGD&T™ Analysis of the ASME Y14,5 2009 Standard 3d. 3e. 3f. 3g. 3h. 3i. 3j. 3k. 3l. 4. Movable Datum Target (Simulator) Symbol Composite Feature Control Frames - Increased numbers of Tiers Datum Reference Frame Axis Identifiers: X[A,B,C], Y[A,B,C] and Z[A,B,C] Unequally Disposed Profile Modifier:(U) Non-Uniform Modifier: [NON-UNIFORM] ALL OVER Modifier: (()) Continuous Feature Modifier: Independency Modifier: (I) The “True” Modifier: TRUE
Disappointments Loss of the RFS and RMB Modifier Symbols (S) Failure to Clean up or Eliminate the Concentricity & Symmetry Tools Failure to Clean up the Radius Tools Failure to Clarify the “Datum Feature Shift” Concept A Still only PartiallyAdequate Topic Index. Incomplete Explanation of the Functional Objectives of the “Geometric Tolerance Value” [Tolerance Zone Size] Modifier (L) 4g. Need to Eliminate the Term “Resultant Condition” and Refine the term “Virtual Condition” 4h. Inadequately Precise Definition of a Basic Dimension 4i. Need to Discontinue use of the Word “True” 4a. 4b. 4c. 4d. 4e. 4f.
2. New and Refined Nomenclature,...