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Example of true position geometric control defined by basic dimensions and datum features. Geometric dimensioning and tolerancing (GD&T) is a system for defining and communicating engineering tolerances via a symbolic language on engineering drawings and computer-generated 3D models that describes a physical object's nominal geometry and the permissible variation thereof.
A material condition in GD&T. Means that a feature of size is at the limit of its size tolerance in the direction that leaves the most material on the part. Thus an internal feature of size (e.g., a hole) at its smallest diameter, or an external feature of size (e.g., a flange) at its biggest thickness. The GD&T symbol for MMC is a circled M.
In a technical drawing, a basic dimension is a theoretically exact dimension, given from a datum to a feature of interest. In Geometric dimensioning and tolerancing, basic dimensions are defined as a numerical value used to describe the theoretically exact size, profile, orientation or location of a feature or datum target.
Tolerance analysis is the general term for activities related to the study of accumulated variation in mechanical parts and assemblies. Its methods may be used on other types of systems subject to accumulated variation, such as mechanical and electrical systems.
Each feature can have a size, a distance from other features, and an allowed tolerance set for each element. The international language used to describe physical parts is called Geometric Dimensioning and Tolerancing (colloquially known as GD&T).
It was revised by MIL-STD-8A in 1953, which introduced the concept of modern GD&T "Rule 1". [5] [6] Further revisions have continued to add new concepts and address new technology like computer aided design and model-based definition. A list of revisions follows: [6] ASME Y14.5-2018, "Dimensioning and Tolerancing" Current Standard
English: Symbol used in a feature control frame to specify a feature's description, tolerance, modifier: Regardless of feature size (RFS) (Not part of the 1994 version. See para. A5, bullet 3. Also para. D3. Also, Figure 3-8.)
Technical drawing with references and geometric specifications. A datum reference or just datum (plural: datums [Note 1]) is some geometrically important part of an object—such as a point, line, plane, hole, set of holes, or pair of surfaces—that serves as a reference in defining the geometry of the object and (often) in measuring aspects of the actual geometry to assess how closely they ...