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TWIST DRILLS
TAPS AND DIES - 14001_33

Aviation Boatswains Mate E 3 & 2 - Aviation theories and other practices
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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. 1-34). The maintenance of twist drills and more about how to use them on specific jobs are discussed later. PUNCHES A hand punch is a tool that is held in the hand and struck on one end with a hammer. There are many kinds of punches designed to do a variety of jobs. Figure 1-35 shows several types of punches. Most punches are made of tool steel. The part held in the hand is usually octagonal in shape, or it may be knurled. This prevents the tool from slipping around in the hand. The other end is shaped to do a particular job. When you use a punch, there are two things to remember: 1. When you hit the punch, you do not want it to slip sideways over your work. 2. You do not want the hammer to slip off the punch and strike your fingers. You can eliminate both of these troubles by holding the punch at right angles to the work and striking the punch squarely with your hammer. Figure 1-34.-Representative shanks. Figure 1-35.-Punches. The center punch, as the name implies, is used for marking the center of a hole to be drilled. If you try to drill a hole without first punching the center, the drill will “wander” or “walk away” from the desired center. Another use of the center punch is to make corresponding marks on two pieces of an assembly to permit reassembling in the original positions. Before taking a mechanism apart, make a pair of center punchmarks in one or more places to help in reassembly. To do this, select places, staggered as shown in figure 1-36, where matching pieces are joined. First, clean the places selected. Then, scribe a line across the joint, and center punch the line on both sides of the joint, with single and double marks Figure 1-36.-Punch marking mating parts. 1-22







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