No supplementary references are needed for this task.

1. Introduction

Most work done in a metalworking repair shop is detailed through the use of blueprints and shop drawings. In order to interpret these drawings into workable plans, the repair shop technician must be familiar with the fundamentals of drafting and shop drawings.

That is the purpose of this subcourse, to introduce the student to the fundamentals of drafting and shop drawings. Task one of this subcourse will cover the theory of orthographic projection and freehand drafting.

2. Orthographic Projection

Accurate orthographic drawings are the foundation of all construction drawings. They furnish complete information for construction and repair, as well as present an object in its true proportions as to shape and size. Third-angle orthographic projection is the standard for all mechanical drawings. These drawings have very little pictorial value but are so superior to all other forms of drawings, from the standpoint of the workman and the draftsman, that nearly all working drawings are made in this form.

Orthographic Projection Drawing

a. Views. Orthographic projection is the method of representing the exact shape of an object in two or more views, on planes generally at right angles to each other, by extending perpendiculars from the object to the planes. One of these views is referred to as the "plane" or top view and represents the object as it appears from directly overhead. Another is known as the "elevation" or front view and represents the object as it appears directly from the front. Still another, designated as "side elevation" or side view, supplements the top and front views by giving information not given in these views. Figure 1 (on the previous page) depicts an orthographic projection with three views. There are three additional views that are sometimes, though rarely, used. These views are the bottom, rear, and left side view.

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