Changes and Additions to ASME Y14.5M

There are number of significant changes between each revision of the ANSI/ASME Y14.5M Dimensioning and Tolerancing Standard. It is difficult to grasp the scope of the changes by simply reviewing the standards themselves. ASME has provided lists of the principal changes and improvements in appendices of the recent standards. Although this is a useful listing, it requires users to flip back and forth through both standards to review these changes and improvements.

Summary of Changes

The latest revision of the ASME Y14.5 Geometric Dimensioning and Tolerancing Standard was issued on March 27, 2009. This latest revision was in work for nearly 15 years, far longer than the usual 10 years between revisions. The delay was due largely to the difficulty in incorporating several major changes. The new standard has numerous improvements and additions, giving the GD&T user a more powerful tool to communicate amongst the production team. Unfortunately, as the Y14.5 standard has been enhanced, it has also made the standard more complex. As always, training and preparation is crucial before the new ASME Y14.5 standard can be widely incorporated in industry. Although there are so many changes that it is impossible to even begin listing them here, the following is an attempt to outline some of the major changes and additions to the new Y14.5 standard:

• Many new/changed nomenclature and terminology terms (many terms are added and many terms are clarified).
• Allows use of 3-D CAD models in conjunction with ASME Y14.41- 2003
• Defines customized datum reference frames (degrees of freedom within a datum reference frame can be customized)
• Defines/clarifies X, Y, Z axes of a datum reference frame (right hand rule applies as a default)
• Defines location and size of datum feature simulators using the MMB, LMB, RMB concept for planar datums (the concept of Material Boundary Modifiers is probably the most notable change within the new standard)
• Allows translation for datum simulators (incorporates a datum translation symbol)
• Expands the concept of composite position
• Expands the concept of composite profile
• Allows use of a non-uniform tolerance zone for profile
• Allows position tolerance without a datum reference
• Flatness may be used to control centerplane flatness (formerly centerplane straightness)

An obvious and often repeated question is… when should we move to the new 2009 GD&T standard? One survey has shown that over 60% of companies responding to the survey have no plans to adopt the standard at the present time; the other 40% plan to adopt the new standard within 2 years of release. As with many new revisions to standards or software, there is a natural reluctance to move to the latest revision (with good reason). Any move to the new standard must be accompanied with careful planning; and most importantly, proper training across the entire production team. The new standard contains a number of powerful new methods to communicate design intent, and every effort should be made to migrate to the new Y14.5-2009 standard.