TWIST DRILLS

Remember that the selection of grades of abrasive cloth, the application of oil, and the cleaning between grades applies to polishing, regardless of how the cloth is held or used. Care of Files A new file should be broken in carefully by using it first on brass, bronze, or smooth cast iron. Just a few of the teeth will cut at first, so use a light pressure to prevent tooth breakage. Do not break in a new file by using it first on a narrow surface. Protect the file teeth by hanging your files in a rack when they are not in use or by placing them in drawers with wooden partitions. Your files should not be allowed to rust – keep them away from water and moisture. Avoid getting the files oily. Oil causes a file to slide across the work and prevents fast, clean cutting. Files that you keep in your toolbox should be wrapped in paper or cloth to protect their teeth and prevent damage to other tools. Never use a file for prying or pounding. The tang is soft and bends easily. The body is hard and extremely brittle. Even a slight bend or a fall to the deck may cause a file to snap in two. Do not strike a file against the bench or vise to clean it – use a file card. Safety Never use a file unless it is equipped with a tight-fitting handle. If you use a file without the handle and it bumps something or jams to a sudden stop, the tang may be driven into your hand. To put a handle on a file tang, drill a hole in the handle, slightly smaller than the tang. Insert the tang end, and then tap the end of the handle to scat it firmly. Make sure you get the handle on straight. TWIST DRILLS Making a hole in a piece of metal is generally a simple operation, but in most cases an important, precise job. A large number of different tools and machines have been designed so that holes may be made speedily, economically, and accurately in all kinds of material. To be able to use these tools efficiently, it is important that you become acquainted with them. The most common tool for making holes in metal is the twist drill. It consists of a cylindrical piece of steel with spiral grooves. One end of the cylinder is pointed, while the other end is shaped so that it may be attached to a drilling machine. The grooves, usually called FLUTES, may be cut into the steel cylinder, or the flutes may be formed by twisting a flat piece of steel into a cylindrical shape. The principal parts of a twist drill are the body, the shank, and the point (fig. 1-33). 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. Figure 1-33.-Twist drill nomenclature. 1-21