fThto Foreword is not a part of ASME Y14.5M-1994.)
Additions, modifications, and clarification contained in this revision of ANSI Y14.5M-1982 are intended to improve national and international standardization and to harmonize the United States practices and methodology with the universal standards trend toward more efficient worldwide technical communication. Coordinating and integrating these techniques into and via computer graphics and other electronic data systems for design, manufacture, verification, and similar processes is also a prime objective.
Incorporating this Standard as a vehicle to assist the United States' active participation and competitiveness in the world marketplace is a major goal. The emergence of priorities on total quality management, world-class engineering, and emphasis on compatibility with the International Organization for Standardization (ISO) 9000 series of quality standards has had a significant influence in the work of the Y14.5 Subcommittee.
This revision was initiated immediately after the official release of ANSI Y14.5M-1982 in December 1982 in response to defeued comments from that revision, new conceptual developments, new symbology, and international standards expansion. Twenty-three Subcommittee meetings and numerous working group meetings of the ASME Y14.5 Subcommittee were convened during the developmental period. The meetings were held in various cities around the United States. The Subcommittee's work was coordinated as much as possible with other related ASME committees and other standard developing bodies that share a common purpose on dimensioning and tolerancing or related standards. Particularly close alliance and liaison were sought with the ASME B89 Committee on "Dimensional Metrology," and new committees ASME Y14.5.1 on "Mathematical Definition of Y14.5," and ASME Y 14.5.2 on "Certification of GD&T Professionals."
Of high priority was the continuing United States participation in the development of ISO standards through its U.S. member body, the American National Standards Institute (ANSI). Some members of the Y14.5 Subcommittee have attended and participated in numerous international meetings and activities during and since the last revision of this Standard. Meetings were attended in Paris, France (1981), West Berlin, Germany (1982), New York City, New York (1984), West Berlin, Germany (1987), Zurich, Switzerland (1989), Orlando, Florida (1991), and Cannel, California (1992). United States delegates have served as members and conveners of Working Groups, chaired some TC1Q/SC5
international meetings and have participated in all ISO standards projects on the subject of dimensioning and tolerancing during this period.
In addition to past participation in developing and maintaining all of such ISO standards as ISO 5458, ISO 5459. ISO 2692, ISO 3040. ISO TR 5460. ISO 1660. ISO 406, ISO 129, ISO 8015. and ISO 7083, U.S. delegates have also participated in all new ISO standards development projects. U.S. delegates have provided convenership (chairmanship) to the development of ISO/2692: 1988 DAM1 on "Least Material Condition," ISO 10578 on "Projected Tolerance Zone," and ISO 10579 on "Nonrigid Parts." Current projects related to the revision of ISO 1101, 'Technical Drawings, Geometrical Tolerancing" and ISO 5458, "Positional Tolerancing" also have participation and input by U.S. delegates. Current new work on a revision to ISO 2692 includes consideration of the "principle of reciprocity" (symbol that was originally put forth by the U.S. and Japan in die early 1970's as a proposed standard. It was considered by some countries to be premature for inclusion then and zero positional tolerancing was adopted as a near substitute.
As a recent significant development, the United States, through its member body, ANSI, has received the ISO/TCI0/SC5 Secretariat. Thus, the U.S. inherits the world leadership for standards development on 'Technical drawings, product definition and related documentation, geometrical dimensioning and tolerancing." Work will continue on maintenance of existing standards and the development of new standards related to geometrical tolerancing.
The conflict in principle regarding limits of size between the "envelope principle" (Taylor Principle, Rule #1) and the "independency principle" continues, although somewhat abated. Issuance of ISO 8015:1985, 'Technical Drawings-Fundamental Tolerancing Principle," features the independency principle but allows the option of the envelope principle by either reference to a national standard (for example, ASME Y14.5M-1994) on the drawing, or by invoking the symbol 0. The Y14.5 Standard continues to advocate and use the envelope principle (boundary of perfect form at MMC of the individual feature) that has been traditionally used in the U.S. and widely accepted elsewhere.
The least material condition © concept is expanded. More complete coverage on this subject is to be considered in future revisions as the state of the art progresses.
Significant steps are taken in this revision to resolve some long-standing differences between the Y14.5 and ISO practices. As U.S. delegates also play a significant role in the development and maintenance at the level of international standards, these differences are eventually tempered and resolved by a merging of these dual objectives. In addition, some long-range planning by the Y14.5 activity has also now materialized in the transition to eliminating these differences. Two significant changes found in this revision are adoption and extension of the universal datum feature symbol and discontinuance of the use of the RFS symbol (S). Other changes, additions, extensions of principles, and resolution of differences are listed in Appendix A, "Principal Changes and Improvements."
The technical expertise and experience of the Y14.5 Subcommittee are provided by the dedicated interests and resources of its personnel. Its members represent a broad cross section of U.S. industry, the Department of Defense (DOD), educational institutions, national laboratories, professional societies, and members of the private sector. The Subcommittee encourages participation by all and works diligently to achieve a consensus on all matters. It seeks a balance between past practices, state of the art. national and international standards, new technology, computer and electronic integration, and most importantly, the understandability of the technical data contained in the Standard itself. Since members are also users of the Standard, a "jury of peers" is constantly present to ensure, as well as possible, that all voices are heard and satisfactory compromises are made in the interests of all users. Through the due process of final approval procedures via ASME, ANSI, DOD, and public review, the Standard achieves its final make-up as the result of the voluntary consensus standard system.
The expansion and extension of principles of the composite positional tolerancing concept occupied a sizable segment of the Subcommittee's time and resources during this revision. This valuable concept, originally born out of need for a convenient method to state two requirements together for a pattern of features, one the "pattern-locating tolerance" (larger tolerance) and the other the "feature-relating tolerance" (smaller tolerance), gave rise to the need for further clarification and coverage in this revision. As these principles are extended from the original examples, first introduced in ANSI Y 14.5-1973, varying interpretations are possible where a secondary datum feature is added to the feature-relating tolerance zone frame. Since the original coverage in ANSI Y 14.5-1973 made no attempt to indicate clearly an interpretation representing this extension of principle, varied applications and interpretations have occurred during the interim, each supposedly having some support from the original Standard example and text. ANSI Y14.5M-1982 repeated the same examples, added two figures (Figs. 142 and 143), and made a slight change of words in the text. The changes and additions in this revision eventually highlighted the areas of question and the Subcommittee debated this issue with many prolonged and in-depth discussions. As a result, the composite tolerancing text and figures have now been expanded to enhance and clarify applicability. To effect this clarification and expansion, and to "set the standard," an explicit meaning has been assigned to the feature-relating tolerance frame for composite positional tolerancing control. The feature-relating tolerance can no longer be interpreted as including location of the pattern. Section 5 clarifies the application of composite tolerancing and contrasts it with the use of two single-segment feature control frames.
Since profile composite tolerancing is now also introduced into the Standard, its feature-relating tolerance frame likewise controls the orientation of the profile to the datums without regard to the basic dimensions that locate the profile. Section 6 further explains the details of composite profile tolerancing.
Although the continuity and stability of the technical content of the Standard are paramount, numerous changes, additions, and clarifications have taken place in this revision. To meet the objectives and purposes of the Standard as before referenced, it must remain dynamic and is, thus, subject to modification as deemed necessary. For help in using this Standard and to isolate those areas and subjects involving any changes or additions of consequence, refer to Appendix A. A detailed compendium of changes and additions is provided.
Suggestions for improvement of this Standard will be welcomed. They should be sent to The American Society of Mechanical Engineers; Attention: Secretary. Y14 Main Committee; 345 East 47th Street; New York. NY 10017.
This revision was approved as an ASME Standard on March 14, 1994. and as an American National Standard on January 5. 1995.
ASME STANDARDS COMMITTEE Y14 Engineering Drawing and Related Documentation Practices
(The following is the roster of the Committee at the time of approval of this Standard.)
Was this article helpful?