Drawing is often called the universal language. Drafting is the particular phase of drawing that engineers and designers use to convey and record ideas or information necessary for the con-struction of structures and machines. There are definite rules of usage to ensure that the same meaning is conveyed at all times and to enable those who learn the rules to interpret what is presented in a drawing. In contrast to pictorial drawings, such as paintings of landscapes and living things, engineering drawings use a graphical language to describe every integral part of an object. As an Engineering Aid, you will specialize in engineering drawings, whereas the Illustrator Draftsman will specialize in pictorial drawings. In studying this chapter, you will learn that drafting is classified into types, such as technical, illustrative, mechanical, freehand, and engineering drafting. Then you will go on to learn about charts, graphs, drafting guidelines, and a variety of instruments and materials, all of which are designed to help you perform your drafting duties. This chapter also contains many pointers that will help you operate, adjust, and maintain your drafting instruments.

Generally, drafting is classified according to its purpose or the means by which it is accomplished.

TECHNICAL AND ILLUSTRATIVE DRAFTING

MECHANICAL AND FREEHAND DRAFTING

The term illustrative drafting is not commonly used in construction drafting. MECHANICAL DRAFTING, as distin-guished from freehand drafting, is any drawing in which the pencil or pen is guided by mechanical devices, such as compasses, straightedges, and french curves. In FREEHAND DRAFTING the pencil or penis guided solely by the hand of the draftsman. Sketches are the result of freehand drafting. With the exception of lettering, most technical drafting is mechanical drafting in this sense of the term.

In a different sense, the term mechanical applies to certain types of industrial or engineering drawings, regardless of whether the drawings are done mechanically or freehand. Some authorities confine the term, used in this sense, to the drawing of machinery details and parts. Others confine it to the drawing of plumbing, heating, air conditioning, and ventilating systems in structures. In the SEABEEs, mechanical drawing means the arrangements of machinery, utility systems, heating, air conditioning, and ventilating systems.

As an Engineering Aid, you will be primarily concerned with the following broad types of engineering drafting:

1. Topographic drafting, or drafting done in connection with topographic and civil engineering surveys. It may include drawings not directly related to topographic maps, such as plotted profiles and cross sections.

2. Construction drafting, or drafting of architectural, structural, electrical, and mechanical drawings related to structures.