5.2 Linear, angular, and radial dimensioning
3 min read•august 13, 2024
Dimensioning is crucial in technical drawings. Linear dimensions show length, width, and height, while angular dimensions measure angles between lines or surfaces. Radial dimensions specify the size of arcs and circles. These techniques work together to fully define object geometry.
Proper placement and style of dimensions are key for clarity. Linear dimensions use extension lines and arrowheads, angular dimensions use arc symbols, and radial dimensions use center marks. Combining these methods logically helps avoid redundancy and ensures clear communication of design intent.
Linear Dimensions on Drawings
Indicating Measurements
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Module 38: Dimensioning – Part 2 – Introduction to Drafting and AutoCAD 2D View original
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- Linear dimensions indicate the length, width, height, or depth of an object or feature using a with arrowheads, dimension text, and extension lines
- Architectural units (feet and ) or metric units () are commonly used for linear dimensions in technical drawings, depending on the industry and project requirements
- Leaders and annotations can be used to provide additional information or clarify specific dimensions when necessary (material specifications, surface finishes)
Placement and Styles
- Dimensions should be placed outside the object boundary whenever possible to maintain clarity, with a visible gap between the object and the beginning of the extension lines
- Dimensioning styles, such as baseline, chain, or , are chosen based on the complexity and layout of the object being dimensioned
- establishes a common baseline and measures each feature from that reference
- Chain dimensioning places dimensions end-to-end, with each dimension starting where the previous one ends
- Ordinate dimensioning uses perpendicular reference lines (datums) to locate features
Angular Dimensioning Techniques
Measuring Angles
- Angular dimensions define the measure of an angle between two lines, surfaces, or features using an with arrowheads and angular dimension text
- Angles are typically measured in degrees (°), with a positive angle measured counterclockwise and a negative angle measured clockwise from a horizontal reference line
- The angle vertex is indicated by extending the two lines forming the angle slightly beyond their intersection point
Slopes and Inclines
- Slope dimensions specify the steepness of an inclined line or surface, expressed as a ratio of vertical rise to horizontal run (1:5 or 20%)
- Angular dimensions for slopes are typically placed parallel to the sloped line or surface, with the dimension text oriented accordingly
- Slope angles can also be expressed in degrees, where a 45° slope corresponds to a 1:1 ratio
Radial Dimensioning for Arcs and Circles
Radius and Diameter
- Radial dimensions specify the radius or diameter of arcs, circles, or rounded features using a radial dimension line with an arrowhead, dimension text, and a or centerlines
- The radius symbol (R) or diameter symbol (Ø) is placed before the dimension value to indicate whether the dimension represents a radius or diameter
- Radius dimensions extend from the center point to the arc or circle
- Diameter dimensions extend across the entire width of the circle, passing through the center point
Center Marks and Centerlines
- Center marks are used to indicate the center point of a circle or arc, while centerlines are used for larger circles or when the center point is located outside the drawing view
- Concentric circles or arcs can be dimensioned using multiple radial dimensions, with each dimension line extending from the center point to the respective circle or arc
- Centerlines are typically drawn using long-short-long line patterns to distinguish them from object lines
Combining Dimensioning Techniques
Logical Organization
- Complex objects often require a combination of linear, angular, and radial dimensions to fully define their geometry and ensure clear communication of design intent
- Dimensions should be organized and positioned in a logical sequence, typically starting with overall dimensions and progressively detailing smaller features or sub-components
- Use dimension grouping or staggering techniques to prevent dimension lines and text from overlapping or interfering with each other (alternate placement above and below the dimension line)
Avoiding Redundancy
- Avoid redundant dimensions or dimensions that can be easily derived from other provided dimensions to maintain drawing clarity and reduce clutter
- Ensure that the combination of dimensions provides sufficient information for manufacturing, assembly, or inspection purposes, considering tolerances and requirements when necessary
- Review the dimensioned drawing to confirm that all necessary dimensions are included and that the object geometry is fully defined without ambiguity or missing information
Key Terms to Review (20)
Angular dimensioning: Angular dimensioning is a method used in technical drawing to specify the angle between two lines or surfaces. This technique is essential for accurately conveying geometric relationships in designs, especially in mechanical and architectural drafting. It allows for precise communication of angles, which is crucial for assembly and fabrication processes.
ANSI Standards: ANSI standards refer to the guidelines established by the American National Standards Institute, which ensure consistency and quality in various fields, including engineering and design. These standards cover everything from technical drawings to materials specifications, helping professionals maintain a uniform approach to drafting and design practices.
Arc symbol: An arc symbol is a graphical representation used in technical drawings to indicate the radius of a circular arc. This symbol not only shows the arc's curvature but also provides essential information regarding its dimensional attributes, such as the radius measurement and the center point of the arc. It plays a crucial role in conveying precise information about the geometry of objects in design and drafting.
Architectural drawings: Architectural drawings are detailed representations of a building or structure, created to communicate design intent, dimensions, materials, and other essential information for construction. They serve as the foundational documents for architects and builders, illustrating both the aesthetic and functional aspects of a project while incorporating various forms of dimensioning techniques to ensure accuracy in the design.
Baseline dimensioning: Baseline dimensioning is a method of specifying the location of features on a part using a common reference point, known as the baseline, from which all dimensions are measured. This approach simplifies the interpretation of the drawing and helps maintain consistency in manufacturing by reducing cumulative tolerances. It provides a clear framework for understanding the spatial relationships between features, especially in complex designs.
Center Mark: A center mark is a symbol used in drafting and design to indicate the center point of a circular or cylindrical feature. It is crucial for both linear and radial dimensioning, as it allows drafters to communicate the exact location of features that require symmetrical or concentric relationships. Proper placement of center marks enhances clarity in technical drawings, ensuring that measurements are easily interpreted and accurately represented.
Centerline: A centerline is a line that defines the midpoint of a feature or object, serving as a reference for alignment and symmetry in drafting and design. It is crucial for conveying the geometric layout of components and is commonly used in linear, angular, and radial dimensioning to ensure accurate measurements and proper assembly of parts.
Dimension Line: A dimension line is a thin, solid line used in technical drawings to represent the extent and direction of a dimension. It connects extension lines and is often marked with numerical values indicating the size or distance of an object in the drawing. Dimension lines are critical for providing clear measurements, which play a vital role in understanding the scale and proportions of designs.
Dimension tool: The dimension tool is a feature in drafting and design software that allows users to create and manage measurements on their drawings. This tool is essential for conveying the precise size, shape, and location of features within a design, helping to ensure accuracy and clarity. By utilizing different dimensioning standards and styles, along with linear, angular, and radial dimensioning methods, the dimension tool plays a crucial role in effective communication within technical drawings.
Engineering drawings: Engineering drawings are detailed and precise representations of objects, structures, or systems that communicate the necessary information for construction, manufacturing, or assembly. They serve as a universal language in engineering, providing specifications, dimensions, and tolerances to ensure that the end product meets the required standards and functions as intended.
Extension line: An extension line is a thin, solid line that indicates the extent of a dimension from a particular feature on a drawing. These lines help clarify where the measurement starts and ends, ensuring that dimensions are accurately interpreted in relation to the object being represented. They are essential for clear communication in technical drawings, particularly when combined with other dimensioning elements like dimension lines and leaders.
Fit: Fit refers to the relationship between two or more parts in terms of their dimensions and how well they work together in an assembly. It involves ensuring that the parts meet specified tolerances to achieve the desired level of clearance or interference, which is crucial for proper functioning and performance of mechanical systems.
Inches: Inches are a unit of length commonly used in the United States and other countries that rely on the imperial system. This measurement is crucial in various fields like drafting, engineering, and construction, as it provides a standard way to define dimensions and sizes. Understanding inches allows for accurate scaling and representation of objects, ensuring that designs and constructions meet specified requirements.
ISO Standards: ISO standards are internationally recognized guidelines and specifications that ensure quality, safety, efficiency, and interoperability in various industries. These standards help streamline processes and improve communication among stakeholders by establishing a common framework. They relate to many areas of design and drafting, influencing precision input, line types, object properties, tolerances, dimensioning, and overall layout configuration.
Leader Lines: Leader lines are lines used in technical drawings to connect a specific note or label to the object or feature being described. They help clarify the meaning of annotations, such as dimensions or notes, by pointing directly to the relevant area of the drawing. These lines can enhance the clarity of technical documents, making it easier for viewers to understand relationships between features and associated notes.
Linear dimensioning: Linear dimensioning is a method used in technical drawing to specify the exact measurements of an object by indicating its length, width, height, and other linear features. This technique is crucial in conveying precise dimensions needed for manufacturing and construction processes, ensuring that parts fit together correctly. By providing clear and accurate measurements, linear dimensioning enhances communication among designers, engineers, and builders.
Millimeters: Millimeters are a unit of measurement in the metric system, commonly used to quantify length or distance. This small metric unit is crucial for precision in design and engineering, particularly when configuring page layouts, establishing coordinate systems, and creating accurate dimensions. Understanding millimeters allows designers to ensure that their work aligns perfectly with industry standards and specifications.
Ordinate Dimensioning: Ordinate dimensioning is a method used in technical drawings that specifies the location of points based on their distance from a reference line or plane, typically the x and y axes. This approach simplifies the measurement process and enhances clarity by allowing dimensions to be referenced directly to a fixed point, rather than relative to other features, making it particularly useful for complex shapes.
Radial dimensioning: Radial dimensioning is a method of indicating the size of a circle or arc by specifying the distance from the center of the circle to its edge. This technique is essential for accurately conveying measurements in technical drawings, particularly when dealing with circular features. Radial dimensioning helps to clarify the layout and proportions of designs, ensuring that all dimensions are communicated clearly for manufacturing or construction purposes.
Tolerance: Tolerance refers to the permissible limit or limits of variation in a physical dimension, measured from a nominal value. It is crucial in design and manufacturing, as it determines how much deviation from a specified measurement is acceptable without affecting the functionality or performance of a part. Understanding tolerance is essential for ensuring that parts fit together correctly and function as intended, which connects deeply with precision input and constraints, as well as dimensioning techniques.