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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.
The two-dimensional measures above find one-dimensional counterparts in straightness measures, [5] defined by ISO 12780 on a cross-section (the plane curve resulting from the intersection of the surface of interest and a plane spanned by the surface normal): least squares reference line; minimum zone reference lines; local straightness deviation
Whereas dial test indicators will give a foreshortened reading if their tips are on an angle to the surface being measured (cosine error), a drawing callout of FIM is defined as referring to the distance traveled by the extremity of the tip—not by the lesser amount that its lever-like action moves the needle.
ASME Y14.5 is a standard published by the American Society of Mechanical Engineers (ASME) to establish rules, symbols, definitions, requirements, defaults, and recommended practices for stating and interpreting Geometric Dimensions and Tolerances (GD&T). [1]
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.
Geometrical Product Specification and Verification (GPS&V) [1] is a set of ISO standards developed by ISO Technical Committee 213. [2] The aim of those standards is to develop a common language to specify macro geometry (size, form, orientation, location) and micro-geometry (surface texture) of products or parts of products so that the language can be used consistently worldwide.
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.
they can measure surfaces through transparent medium such as glass or plastic film; non-contact measurement may sometimes be the only solution when the component to measure is very soft (e.g. pollution deposit) or very hard (e.g. abrasive paper). Vertical scanning: Coherence scanning interferometry; Confocal microscopy; Focus variation