BASIC COMPUTER AIDED DRAFTING (CAD)

The process of preparing engineering drawings on a computer is known as computer-aided drafting (CAD), and it is the most significant development to occur recently in this field. It has revolutionized the way we prepare drawings.

The drafting part of a project is often a bottleneck because it takes so much time. Drafter's spend approximately two-thirds of their time "laying lead."

Figure 2-12.-Example of an ellipse.

Figure 2-13.-A reverse (ogee) curve connecting two parallel planes.

But on CAD, you can make design changes faster, resulting in a quicker turn-around time.

CAD also can relieve you from many tedious chores such as redrawing. Once you have made a drawing you can store it on a disk. You may then call it up at any time and change it quickly and easily.

It may not be practical to handle all of the drafting workload on a CAD system. While you can do most design and drafting work more quickly on CAD, you still need to use traditional methods for others. For example, you can design certain electronics and construction projects more quickly on a drafting table.

A CAD system by itself cannot create; it is only an additional and more efficient tool. You must use the system to make the drawing; therefore, you must have a good background in design and drafting.

In manual drawing, you must have the skill to draw lines and letters and use equipment such as drafting tables and machines, and drawing aids such as compasses, protractors, triangles, parallel edges, scales, and templates. In CAD, however, you don't need those items. A cathode-ray tube, a central processing unit, a digitizer, and a plotter replace them. Figure 2-14 shows some of these items at a computer work station. We'll explain each of them later in this section.

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