I'ROST SCREWS AND THEIR MANUFACTURE. 



159 



scriptioii is appended. The screws are formed of square steel 

 from- J- to ^ inch in thickness, a special anvil being employed 

 (fig. 114, c and a). The mould for forming the shank (a, a) 

 is held in the centre of the anvil in two special guides {n, n). 

 It is of steel, and possesses, as shown by the figure, two 

 moulds or grooves of dissimilar breadth, of which that on the 

 right is for the preparation, and that on the left for the com- 

 pletion of the shank. These moulds correspond also to the 



Fig. 114. — Anvil foi- making screws, a. mould for forming shank; b, cutter; c, mould for 

 making sharp-headed screws ; d, plate carrying set screws, g, and held in position by the 

 two screws, e, e ; /, die carrying the moulds, a, a. This can be set at any distance from 

 the plate, d, by moving the set screws, (j. The length of the shank is thus fixed ; A, 

 forging hammer. 



forging hammer {li), which is slid into the grooves {n) and 

 comes down on the piece of square steel : as soon as the 

 hammer Qi) and the mould {a) come in contact, the shank is 

 of the proper thickness. Although the steel is drawn out by 

 working in the right mould, it is still too large for the left, 

 into which it is next inserted, and in which it is finished. 

 The difference in the diameter of the two moulds determines 

 the amount of elongation which th6 shank undergoes in the 

 process. In making blanks or blunt screws, the height of 

 the screw is next marked, the stop (/) placed in position, the 

 heated bar passed first into the mould {a) and then into the 

 mould on the left, and forged until the forging hammer and 

 mould come in contact. It is then cut off, roughly finished. 



In making chisel-headed screws (fig. 115) the mould (c) is 

 first used, and the same process gone through to form the shank 



