9 Dimensioning

Identify terms and measurements associated with dimensioning mechanics. Identify symbols that have been standardized for dimensioning notations. Explain the choice and placement rules drafters use. Identify and discuss various systems and methods for dimensioning. Describe the additional types of dimensions used in special ways.

Dimensioning Mechanics Dimensioning mechanics involves the size and spacing for all components of the dimension

Standard Dimensioning Symbols

Placement of Dimensional Values

Small Dimension Mechanics

Angular Dimension Mechanics

Dimensioning Rules of Choice and Placement Contour rule

Dimensioning Rules of Choice and Placement Cylinder rule

Dimensioning Rules of Choice and Placement Bolt circles

Dimensioning Rules of Choice and Placement Angles

Dimensioning Rules of Choice and Placement Datums

Dimensioning Rules of Choice and Placement Rounded ends

Reference Dimensions Not for manufacturing purposes Informational reference only

Tabular Dimensions Dimensions are sometimes placed in tables for clarity Tabular dimensions also allow for multiple parts on one drawing

Tabular Dimensions

Hole Charts Often used for a part with a large number of repetitive features

Arrowless Dimensioning Sometimes called coordinate or ordinate dimensioning

Dual Dimensioning Values in U.S. customary and metric units are both given, with one value in brackets

What are dimensioning mechanics? Instructions or guidelines for what size and spacing to use for all of the components and dimensions.

In the past, the abbreviation DIA followed a dimension value to indicate a diameter. What method is used now? The diameter symbol () precedes the dimensional value.

What is contour dimensioning? A rule regarding dimensioning choice and placement that states a feature should be dimensioned in the view where its shape is most descriptive.

What is the difference between location, size, and reference dimensions? Location dimensions indicate the location of a feature. Size dimensions indicate the size of the feature. Reference dimensions are for informative purposes only—not layout, machining, or inspection—and may be related to location or size.

What are three other terms for arrowless dimensioning? Ordinate, coordinate, and datum dimensioning