A reference dimension is a dimension on an
engineering drawing
An engineering drawing is a type of technical drawing that is used to convey information about an object. A common use is to specify the geometry necessary for the construction of a component and is called a detail drawing. Usually, a number of ...
provided for information only.
Reference dimensions are provided for a variety of reasons and are often an accumulation of other dimensions that are defined elsewhere
[.] (e.g. on the drawing or other related documentation). These dimensions may also be used for convenience to identify a single dimension that is specified elsewhere (e.g. on a different drawing sheet).
Reference dimensions are not intended to be used directly to define the geometry of an object. Reference dimensions do not normally govern manufacturing operations (such as machining) in any way and, therefore, do not typically include a dimensional tolerance (though a tolerance may be provided if such information is deemed helpful). Consequently, reference dimensions are also not subject to dimensional inspection under normal circumstances.
Reference dimensions are commonly used in CAD software along with
constraints that usually denote the opposite: mandatory dimensions to be precisely followed.
Notation
In Computer-Aided Design (
CAD
Computer-aided design (CAD) is the use of computers (or ) to aid in the creation, modification, analysis, or optimization of a design. This software is used to increase the productivity of the designer, improve the quality of design, improve co ...
) it's commonly used to denote dimensions.
REF
Prior to use of modern CAD software, reference dimensions were traditionally indicated on a drawing by the abbreviation "REF" written adjacent to the dimension (typically to the right or underneath the dimension).
However, standard ASME Y14.5 has changed the way references are marked and the abbreviation "REF" has been replaced with the use of parentheses around the dimension. As an example, a distance of 1500 millimeters might be denoted by instead of .
This implementation has followed in modern
CAD software
Computer-aided design (CAD) is the use of computers (or ) to aid in the creation, modification, analysis, or optimization of a design. This software is used to increase the productivity of the designer, improve the quality of design, improve co ...
that makes use of parentheses as the default denotation method whenever reference dimensions are "automatically" created by the software. The method for identifying a reference dimension (or reference data) on drawings is to enclose the dimension (or data) within parentheses.
See also
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Engineering drawing abbreviations and symbols
Engineering drawing abbreviations and symbols are used to communicate and detail the characteristics of an engineering drawing. This list includes abbreviations common to the vocabulary of people who work with engineering drawings in the manufactur ...
**
Geometric dimensioning and tolerancing
Geometric Dimensioning and Tolerancing (GD&T) is a system for defining and communicating engineering tolerances and relationships. It uses a symbolic language on engineering drawings and computer-generated three-dimensional solid models that exp ...
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ASME Y14.5
References
{{Reflist
External links
Y14.5 Dimensioning and Tolerancing 2018,
ASME
The American Society of Mechanical Engineers (ASME) is an American professional association that, in its own words, "promotes the art, science, and practice of multidisciplinary engineering and allied sciences around the globe" via "continuing ...
Technical drawing