Orthographic views

They are 2D images of a 3D object obtained by viewing it from different orthogonal directions. They are created

using orthographic projection principles. Projection is the graphic technique of extending points on a 3D object

by straight lines (linear projection) so as to create its image(s) on a projection, picture or image plane.

This allows a 3D object to be accurately represented on a 2D plane. The image plane is an imaginary transparent

flat surface that coincides with the drawing surface. In practice the drawing surface may be a paper or computer

screen.

Standard Views

Though there are six principal views, three have been chosen as standard views.

The U.S. standard views are Top, Front and Right-side views. These are based on the third angle

projection in which the object is assumed to be located in the third quadrant.

The European standard views are Front, Top and Left-side views. These are based on the first angle

projection in which the object is assumed to be located in the first quadrant.

First

Auxiliary Views

There are times when the six principal views will not completely describe an object.

This is especially true when there are inclined or oblique planes or features on an object. For

these cases, a special orthographic view called an auxiliary view can be created.

Additionally, auxiliary views are used to show an object from an odd angle for any of a variety of

reasons.

Definition

An auxiliary view is an orthographic view which is projected onto any plane other than the frontal,

horizontal, or profile plane.

• An auxiliary view is not one of the six principal views.

• One of the principle reasons for drawing auxiliary views is to show a surface at true size and shape.

None of them gives the true

shape of ABCD

A viewing plane parallel to the surface is required to get

true size and shape.

• Fold lines represent the edges of the “glass box”

• Orthographic lines are projected from adjacent

views across fold lines.

• Object distances from fold lines are obtained from

related views.

• Reference Planes are a variation on the glass box.

• They appear as edges in the auxiliary & related views.

• Lengths perpendicular to the fold line are measured relative to the reference plane

There are three classes of auxiliary views:

primary

Secondary

Tertiary

Steps to construct(draw)

an auxiliary view

Exercise 3 Exercise 4

Exercise 5