DETAILS OF DERRICKS. 



Where compressed air is available a pneumatic field riveter is used for driving rivets. Pneu- 

 matic tii-ltl rivi-ters are of two types: (a) jaw riveters that buck-up the rivet and form the head as 

 in shop riveters; and (6) a pneumatic gun that is held against the rivet by the riveter, the rivet 

 being bin -kccl-up with a dolly as in hand riveting or with a pneumatic dolly. The pneumatic gun 



'Guy Lines^ 



"-Boom or Topping Lines 



Boom Lines, ^ 



5oom Lines 



(Fall Lines or 

 ** Hois ting L ines 



GUY DERRICK 



-Bull Wheel 



GUY DERRICK WITH BULL WHEEL 



-Boom Lines 



r-Masb 



fall Lines or 

 * Hois ting Lines ' 



,-BulI Wheel 



STIFF LES DERRICK W/TH BULL WHEEL 



BULL WHEEL 



FIG. 19. DETAILS OF DERRICKS. 



is more convenient and is commonly used. A rivet snap is used in the air gun. Good rivets can 

 be driven by hand, but the work of the pneumatic riveter is more uniform and most specifications 

 for erection of structural steel call for its use. Several railroad bridge specifications now 

 require that hand driven field rivets be calculated for only four-fifths of the allowable stresses on 

 machine driven field rivets. While more rivets can be driven with an air gun than by hand, the 

 added expense for air makes the cost of driving nearly the same as for hand driven rivets. 



