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