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Orthographic Views

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Learn how to create and interpret orthographic views. Views are created using third-angle projection in compliance with ANSI standards and conventions. The differences between first-angle and third-angle projections are demonstrated. Five exercise problems are included to help students learn to work with the two different standards. Also included are section views, auxiliary views, and broken views. Several of the projects require that a 3D solid model be drawn from a given set of orthographic views to help students develop visualization skills.

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4-1 Introduction

Orthographic views are two-dimensional views used to define a three-dimensional model. More than one orthographic view is needed to define a model unless the model is of uniform thickness. Standard practice calls for three orthographic views, a front, top, and side view, although more or fewer views may be used as needed.

There are two sets of standards used to define the projection and placement of orthographic views: the American National Standards Institute (ANSI) and the International Organization for Standardization (ISO). The ANSI calls for orthographic views to be created using third-angle projection and is the accepted method for use in the United States. See the American Society of Mechanical Engineers publication ASME Y14.3-2003. Some countries, other than the United States, use first-angle projection. See ISO publication 128-30.

This chapter will present orthographic views using third-angle projections as defined by ANSI. However, there is so much international commerce happening today that you should be able to work in both conventions and in either inches or millimeters.

Figure 4-1 shows a three-dimensional model and three orthographic views created using third-angle projection and three orthographic views created using first-angle projection. Note the differences and similarities. The front view in both projections is the same. The top views are the same but are in different locations. The third-angle projection presents a right-side view, while the first-angle projection presents a left-side view.

Figure 4-2 shows the drawing symbols for first- and third-angle projections. These symbols can be added to a drawing to help the reader understand which type of projection is being used. These symbols were included in the projections presented in Figure 4-1.

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