250 



APPLIED SCIENCE 



made by machine. Wood screws were originally made with 

 blunt points. It was then necessary to make a hole in the 

 wood before the screw could be driven. In the nineteenth 

 century, the invention of the gimlet-pointed screw obviated 



FIG. 109. A Nail Factory. The wire is fed into machines which cut 

 and shape the wire into nails. 



the necessity for this preparatory process. When first 

 manufacturing these screws by machinery, the metal was 

 cut out between the threads. This method tended to weaken 

 them, and they frequently broke when driven into wood. 

 Later the method of manufacture which is in use today was 

 introduced. The modern process consists of raising the 

 thread by a system of rolling and compression. An operator 

 feeds into a s.rew-making machine wire of various sizes, and 

 the machine cuts off the wire at the desired length and turns 

 the screw. The hammer part of the machine then strikes 

 the exposed end of the wire, shaping the head of the screw. 

 This method makes a screw that is strong and that possesses 



