Part 11 Dimensioning a Drawing

Part 11: Sizing It Up - Dimensioning the Drawing

Important Issues

One needs to be aware of the number of decimal places shown in the drawing. This is the number of digits shown after the decimal point, and it implies a degree of accuracy.

NOTE:

This accuracy varies according to the conditions. If surveying the digits may be 0.0. But in manufacturing a part it could be as precise as 0.000.

Summary:

Dimensions are added to show the size, shape, and location of features on an object, product, buildings, floor plans, etc. Creating dimensions becomes extremely important. If the geometric objects in the drawing are created accurately enough, then the dimensions can be automatically created by the CAD system.

Elements in Dimensioning

Some dimensioning terms you should know. See examples, indicated in red, that follow:

1. Dimension lines
2. Extension lines
3. Terminators
4. And Dimension Text

Dimension Lines

Methods of Dimensioning

There are basic methods used to dimension various objects, structures, architectural plans, etc.

1. Linear
2. Angular
3. Radial, Diameter/Radius
4. Leaders
5. Annotations

Extension Lines

Terminators

Dimension Text

Linear

Linear dimensions can be horizontal, vertical, or aligned. With aligned dimensions, the dimension line is parallel to the line (imaginary or real) between the extension line origins. Baseline (or parallel) and continued (or chain) dimensions are series of consecutive dimensions that are based on a linear dimension. See figures below.

Linear

Horizontal and Vertical

Angular

Angular dimensions measures the angle between two lines or three points. To measure the angle between two radii of a circle, you select the circle and specify the angle endpoints. With other objects, you select the objects and then specify the dimension location.

See figure at right.

Radial

Radial dimensions measure the radii and diameters of arcs and circles with optional centerlines or a center mark. See figure below.

Leaders/Terminators

You can create a leader line from any point or feature in a drawing and control its appearance as you draw. Leaders can be straight line segments or smooth spline curves. See following figure.

Annotations

Annotation objects include dimensions, notes, and other types of explanatory symbols or objects commonly used to add information to your drawing. Annotation objects provide information about a feature, such as the height/length of a wall. The diameter of a bolt, or the specifications of a product, i.e.. Materials, quantity, color, etc.. See the following examples.