While traditional tooling has changed little in the past 60  years, significant changes have been made in rivet gun  ergonomics. Reduced vibration rivet guns and bucking bars  have been developed to reduce the incidence of carpal tunnel  syndrome and enhance operator comfort.  of rivet squeezers—hand, pneumatic, and pneudraulic— operate on the same principles. In the hand rivet squeezer,  compression is supplied by hand pressure; in the pneumatic  rivet squeezer, by air pressure; and in the pneudraulic,  by a combination of air and hydraulic pressure. One jaw  is stationary and serves as a bucking bar, the other jaw is  movable and does the upsetting. Riveting with a squeezer is  a quick method and requires only one operator. Pneumatic guns are used in conjunction with interchangeable  rivet sets or headers. Each is designed to fit the type of rivet  and location of the work. The shank of the rivet header is  designed to fit into the rivet gun. An appropriate header must  be a correct match for the rivet being driven. The working  face of a header should be properly designed and smoothly  polished. They are made of forged steel, heat treated to be  tough but not too brittle. Flush headers come in various sizes.  Smaller ones concentrate the driving force in a small area for  maximum efficiency. Larger ones spread the driving force  over a larger area and are used for the riveting of thin skins. These riveters are equipped with either a C-yoke or an  alligator yoke in various sizes to accommodate any size of  rivet. The working capacity of a yoke is measured by its gap  and its reach. The gap is the distance between the movable  jaw and the stationary jaw; the reach is the inside length  of the throat measured from the center of the end sets. End  sets for rivet squeezers serve the same purpose as rivet sets  for pneumatic rivet guns and are available with the same  type heads, which are interchangeable to suit any type of  rivet head. One part of each set is inserted in the stationary  jaw, while the other part is placed in the movable jaws.  The manufactured head end set is placed on the stationary  jaw whenever possible. During some operations, it may be  necessary to reverse the end sets, placing the manufactured  head end set on the movable jaw. Nonflush headers should fit to contact about the center two- thirds of the rivet head. They must be shallow enough to allow  slight upsetting of the head in driving and some misalignment  without eyebrowing the riveted surface. Care must be taken to  match the size of the rivet. A header that is too small marks  the rivet; while one too large marks the material. Rivet headers are made in a variety of styles.  [Figure 4-88]  The  short, straight header is best when the gun can be brought  close to the work. Offset headers may be used to reach rivets  in obstructed places. Long headers are sometimes necessary  when the gun cannot be brought close to the work due to  structural interference. Rivet headers should be kept clean. Compression riveting (squeezing) is of limited value because  this method of riveting can be used only over the edges of  sheets or assemblies where conditions permit, and where the  reach of the rivet squeezer is deep enough. The three types  A microshaver is used if the smoothness of the material (such  as skin) requires that all countersunk rivets be driven within  a specific tolerance.  [Figure 4-89]  This tool has a cutter, a  stop, and two legs or stabilizers. The cutting portion of the  microshaver is inside the stop. The depth of the cut can be  adjusted by pulling outward on the stop and turning it in  either direction (clockwise for deeper cuts). The marks on the stop permit adjustments of 0.001 inch. If the microshaver  is adjusted and held correctly, it can cut the head of a  countersunk rivet to within 0.002 inch without damaging  the surrounding material.  Rivet Sets/Headers Microshavers Compression Riveting Figure 4-89.  Microshaver.  Figure 4-88.  Rivet headers. 4-39