The flat end of the head is called the face. This end is used for most hammering jobs. The domed end of the hammer is called the peen. The peen end is smaller in diameter than the face, and is useful for striking in areas that are too small for the face to enter. Ball peen hammers are made in different weights, usually 4, 6, 8, and 12 ounces and 1, 1 1/2, and 2 pounds. For most work, a 1 1/2-pound and a 12-ounce hammer will suffice. MALLETS.—A mallet is a soft-faced hammer. Mallets are constructed with heads made of brass, lead, tightly rolled strips of rawhide, plastic, or plastic with a lead core for added weight. A plastic mallet, similar to the one shown in figure 13-1, is the type normally found in the AM’s toolbox. The weight of the plastic head may range from a few ounces to a few pounds; however, the size of the plastic mallet is measured across the diameter of the face. The plastic mallet may be used for straightening thin sheet ducting or for installing clamps. Rotary Rivet Cutters In case you cannot obtain rivets of the required length, rotary rivet cutters may be used to cut longer rivets to the desired length. See figure 13-2. When you use the rotary rivet cutter, insert the rivet part way into the correct diameter hole. Place the required number of shims (shown as staggered, notched strips in the illustration) under the head and squeeze the handles. The compound action from the handles rotates the two discs in opposite directions. The rotation of the discs shears the rivet smoothly to give the correct length (as determined by the number of Figure 13-2.—Rotary rivet cutter. shims inserted under the head). When you are using the larger cutter holes, place one of the tool handles in a vise, insert the rivet in the hole, and shear it by pulling the free handle. If this tool is not available, diagonal-cutting pliers can be used as an emergency cutter, although the sheared edges will not be as smooth and even as when they are cut with the rotary rivet cutter. Rivet Set A rivet set is a tool equipped with a die for driving a particular type of rivet. Rivet sets are used in both hand and pneumatic hammer riveting methods. Rivet sets are available to fit every size and shape of rivet head. The ordinary hand set is made of 1/2-inch diameter carbon steel about 6 inches long. It is knurled to prevent slipping in the hand. Only the face of the set is hardened and polished. Sets for the oval-head rivets (universal, round, and brazier) are recessed (or cupped) to fit the rivet head. When you select a rivet set, be sure that it will provide the proper clearance between the set and the sides of the rivet head and between the surfaces of the metal and the set. Flush or flat sets are used for countersunk and flat-head rivets. To set flush rivets properly, the flush sets should be at least 1 inch in diameter. Special sets, called “draw” sets, are used to “draw up" the sheets being riveted in order to eliminate any opening between them before the rivet is bucked. Each draw set has a hole 1/32 of an inch larger than the diameter of the rivet shank for which it was made. Sometimes, especially in hand-working tools, the draw set and the rivet header are incorporated into one tool. The header consists of a hole sufficiently shallow for the set to expand the driven rivet “bucktail” and form a head on it when the set is struck by a hammer. Figure 13-3 shows a rectangular-shaped hand set that combines the draw and header sets and a flush set used with a pneumatic hammer. Sets used with pneumatic hammers (rivet guns) are provided in many sizes and shapes to fit the type and location of the rivet. These sets are the same as the hand rivet sets except that the shank is shaped to fit into the rivet gun. The sets are made of high-grade carbon tool steel and are heat-treated to provide the necessary strength and wear resistance. The tip or head of the rivet set should be kept smooth and highly polished to prevent marring of rivet heads. 13-2