94 Chapter 5
Purpose of Isometric Drawing.
The task of an isometric drawing is primarily to show a three-dimensional picture in one drawing. It is like
a picture that lacks artistic details. Many utilities workers have difficulty in clearly visualizing a piping or
ducting installation when they are working from a floor plan and an elevation drawing. The isometric
drawing facilitates understanding by combining the floor plan and the elevation. It clearly communicates
the details and clarifies the relationship of the pipes in an installation. Although isometric drawings are
not normally drawn to scale on blueprints, some architects and engineers prefer drawing them to scale.
Isometric drawings, like other types of drawings, follow certain rules and conventions to show three di-
mensions on a flat surface.
Dimensioning Isometric Drawings.
An isometric drawing, or sketch, is dimensioned with extension and dimension lines in a manner some-
what similar to that of a two-dimensional drawing. The extension lines extend from the drawing, and the
dimension lines are parallel to the object line and of equal length to it. Dimensioning the isometric draw-
ing is more difficult because it consists of a single view, with less room available than on three separate
views.
Circles or holes will be skewed or drawn within an isometric square. For example, a circle will ap-
pear elliptical in shape and is actually drawn by connecting a series of four arcs, drawn from the center-
lines of the isometric square. The ellipses may also be drawn with the use of templates. Curved or round
Figure 5.18 A. Orthographic views of an object (third-angle projection). B. Three-view isometric drawings of
the same object.