asme y14.5 geometric dimensioning and tolerancing

Digitally creating a datum from an imperfect datum feature has always been a difficult problem and each CMM software programmer had their own best solution. To be honest, the candidate datum set outlined in previous versions of Y14.5 was not used in the digital equipment without the use of hard fixturing. This will probably have the biggest impact to industry as CMMs and other digital metrology equipment implement this new algorithm. This default stabilization algorithm is officially called the Constrained Least Squares. This can be done with shims on a surface plate or with an official algorithm further outlined in ASME Y14.5.1 Mathematical Definitions of Dimensioning and Tolerancing Principles to be released at the end of 2019. The 2018 version is now using a default stabilized single solution: “the part is to be adjusted to a single solution that minimizes the separation between the feature and the true geometric counterpart”. In previous versions of Y14.5, the standard used the candidate datum set to derive multiple permissible datums (find the datum that works). This applies to a planar datum feature or a datum feature of size referenced at RMB. The biggest change in the standard relates to the establishment of a datum from a datum feature that is unstable (i.e. Application of tolerancing in 3D models is gaining more traction and a lot of the definition updates in Y14.5-2018 have been to accommodate model-based applications. Some outdated or misused concepts have been removed to streamline the document and reduce confusion. You will find minor tweaks to definitions and clarifications of concepts with new figures. The core concepts of Dimensioning and Geometric Tolerancing have not changed. At least half of the 2D figures now have a matching 3D figure. Y14.5 is starting to absorb the 3D representation for model based tolerancing from the Y14.41 standard. This is mostly due to the extra 3D figures for most of the concepts.

The extra thickness of the book seems like a lot has been added, as the book went up from 214 to 326 pages. This makes it easier to flip between the words and figures. The digital pdf version of the standard now has hyperlinks to the correct figures when reading text in the paragraphs. All new ASME standards must now start with sections 1-3 as Scope, References, and Definitions.

The sections have been renumbered to match ASME’s new formatting. The new standard does hold the title of the 2018 completion date even though it wasn’t released until February 2019. I can’t show every change in this article, but I will outline the most notable.Īt first glance, you will notice a few things in the new document.

We have been getting a lot of questions related to the new ASME Y14.5-2018 standard and its principal changes and additions.

Asme y14.5 geometric dimensioning and tolerancing