Figure 1-24.—Twist drill nomenclature.

The principal parts of a twist drill are the body, the shank, and the point (fig. 1-24). The dead center of a drill is the sharp edge at the extreme tip end of the drill. It is formed by the intersection of the cone-shaped surfaces of the point and should always be the exact center of the axis of the drill. The point of the drill should not be confused with the dead center. The point is the entire cone-shaped surface at the end of the drill. The lip or cutting edge of a drill is that part of the point that actually cuts away the metal when drilling a hole. It is ordinarily as sharp as the edge of a knife. There is a cutting edge for each flute of the drill. The shank is the part of the drill that fits into the socket, spindle, or chuck of the drill press. Several types exist (fig. 1-25). The maintenance of twist drills and more about how to use them on specific jobs are discussed later. REVIEW QUESTIONS Q7. Identify the different types of metal-cutting tools. Q8. What are hawks-bill snips used for? Q9. What are hacksaws used for? Q10. What are taps and dies used for? WRENCHES LEARNING OBJECTIVES: Identify the different types of wrenches. Describe the uses of different types of wrenches. List the safety precautions that apply to wrenches. A wrench is a basic tool that is used to exert a twisting force on bolt heads, nuts, studs, and pipes. The special wrenches designed to do certain jobs are, in most cases, variations of the basic wrenches that are described in this section. The best wrenches are made of chrome vanadium steel. Wrenches made of this material are lightweight and almost unbreakable. This is an expensive material, however, so the most common wrenches found in the Navy are made of forged carbon steel or molybdenum steel. These latter materials make good wrenches, but they are generally built a little heavier and bulkier to achieve the same degree of strength as chrome vanadium steel. 1-18 Figure 1-24.—Twist drill nomenclature. Figure 1-25.—Representative shanks.