Movement of air during forward stroke Movement of air during rearward stroke Blank rivet set Beehive spring set retainer Piston Set sleeve Cylinder Exhaust deflector Sliding valve Throttle, trigger Throttle lever Throttle valve Air path Throttle tube Bushing Regulator adjustment screw Figure 4-87.  Components of a rivet gun.  On the other hand, if the gun is too light, it may work harden  the rivet before the head can be fully formed. The riveting action should start slowly and be one continued  burst. If the riveting starts too fast, the rivet header might  slip off the rivet and damage the rivet (smiley) or damage  the skin (eyebrow). Try to drive the rivets within 3 seconds,  because the rivet will work harden if the driving process  takes too long. The dynamic of the driving process has the  gun hitting, or vibrating, the rivet and material, which causes  the bar to bounce, or countervibrate. These opposing blows  (low frequency vibrations) squeeze the rivet, causing it to  swell and then form the upset head.  rivet) is used for normal work. The less powerful 3X gun is  used for smaller rivets in thinner structure. 7X guns are used  for large rivets in thicker structures. A rivet gun should upset  a rivet in 1 to 3 seconds. With practice, an aircraft technician  learns the length of time needed to hold down the trigger.  A rivet gun with the correct header (rivet set) must be held  snugly against the rivet head and perpendicular to the surface  while a bucking bar of the proper weight is held against the  opposite end. The force of the gun must be absorbed by the  bucking bar and not the structure being riveted. When the  gun is triggered, the rivet is driven.  Always make sure the correct rivet header and the retaining  spring are installed. Test the rivet gun on a piece of wood  and adjust the air valve to a setting that is comfortable for  the operator. The driving force of the rivet gun is adjusted by  a needle valve on the handle. Adjustments should never be  tested against anything harder than a wooden block to avoid  header damage. If the adjustment fails to provide the best  driving force, a different sized gun is needed. A gun that is  too powerful is hard to control and may damage the work.  Some precautions to be observed when using a rivet gun are: 3.  Always disconnect the air hose from the rivet gun  when it is not in use for any appreciable length of time. 2.  Never depress the trigger mechanism unless the set is  held tightly against a block of wood or a rivet. 1.  Never point a rivet gun at anyone at any time. A rivet  gun should be used for one purpose only: to drive or  install rivets. 4-38