ABSTRACTATTILIO MENNUTI. Industry Implications of ASME Y14.5-2018 Rule (s) and the "Nested" Principle. (Under the direction of DR. EDWARD MORSE)ASME Y14.5-2018 Section 4.2 Rule S states "Unless otherwise specified (UOS), elements of a surface include surface texture and flaws (e.g., burrs and scratches). All elements of a surface shall be within the applicable specified tolerance zone boundaries." [1]. The newly released rule in the standard effectively puts in writing what the standards committee has been "implying" for years, that every imperfection of the surface should be included in GD&T callouts. This is essentially an impossible task because there is no practical instrument in existence that can measure the actual depth of all imperfections in a part surface - especially in the case of large surfaces. Furthermore, this rule bases the "true value" of the measurand on an unknown feature, like the bottom of a crack or pore. Without a well-defined GD&T measurand, there is no way to claim an uncertainty from measurements. As a result of the inability to quantify surface roughness and surface defects, they have historically been viewed as negligible in GD&T measurement practice. Adhering to the new Y14.5 would call for the inclusion of all surface roughness and defects. Including these truly unknown quantities will lead to significant changes in the reported values of almost all surface measurement machines. As a result of rule s in the Y14.5-2018 standard, an argument can be made that GD&T measurands are not reportable since the true extent of surface roughness and surface defects cannot be completely detected in actual measurement systems. For the purpose of this work, the terms "Size" and "form" will be used to describe aspects of a surface rather than the common definitions outside of GD&T. The Y14.5 standard utilizes the "nested" principle imbedded in GD&T. This plays out in the concept that size includes all elements of the surface (including form, texture, and defects). Similarly, form includes all sub-elements of the surface (including texture and defects). Essentially this means that a form tolerance such as straightness, roundness, flatness, and cylindricity includes the surface’s underlying shape, its waviness, its roughness, and its defects in its reported value. In common practice metrology professionals and measurement suppliers smooth out roughness and defects when they report form results based on a print. Over the years this practice became commonplace and is widely accepted throughout industry. There was never specific literature in any standard claiming it was necessary to include the roughness and defects… until the release of rule s. Under the newly specified method of form GD&T, the vast majority of currently used measurement machines will have to be replaced as they don’t have the capability to include surface roughness and defects in GD&T measurements. In fact, for relatively large surfaces (perhaps in the order of 0.25m by 0.25m), measurement technologies do not commercially exist for measurement according to this requirement.ASME clearly states that Y14.5 is "not intended as a gaging standard" so it should not be used by metrologist as a measurement standard. However, it is important to understand that measurement plans are heavily influenced by Y14.5 because print tolerances are often generated based on conclusions drawn from measurement data. Since the difference between GD&T and the actual measurement plan can be quite ambiguous, the literature in the GD&T standard has a huge impact on common measurement procedures. Furthermore, the combination of the part specification and the meaning of the specification per Y14.5 serves as a contractual agreement between the customer and the measurement supplier. If we are unable to measure, we are unable to do commerce. A measurement plan is often referred to as a supplement to the drawing that was provided by the designer. For the purpose of this work a designer will represent any person working in the drafting discipline and is responsible for assigning part tolerances on a print. An argument can be made that this rule s problem can be addressed with a proper measurement plan. However, section 4.2.2 of the ASME B89.7.2 Measurement Planning standard states "workpiece drawings… define the measurand (for which the measurement plan is to be created.)" [15]. In the case of rule s, the drawing defines a measurand with an unattainable uncertainty. Thus, a measurement plan cannot be created according to standards.Rule s may seem like a miniscule clarification in the grand scheme of the GD&T and manufacturing landscape, however it introduces a significant change in industry. Accepting this change comes at a massive cost. A cost in terms of a shift to a whole new definition of characteristics as well as a commercial cost. This work seeks to explore the implications of the inclusion of surface texture and defects in GD&T. The technical challenges as well as the economic challenges will be discussed as they relate to a "nested" model versus a "partitioned" model for the control of surface geometries.