PORTSMOUTH DOCK- YARD. 1 23 



the blocks are thus sawn into a polygonal figure they are carried to the 

 shaping engine; the object of which is to shape them to the segment of 

 a large circle. For this purpose ten blocks are fixed by their extreme 

 ends between the rims of two equal wheels, fastened upon the same axis. 

 These wheels are then made to turn with amazing rapidity, so as to 

 bring the blocks successively against the edge of a fixed gouge, which 

 thus cuts them to the proper curvature. 



A progressive motion is also given to the gouge, in order to give the 

 blocks their proper curvature, in a direction at right angles to the planes 

 in the wheels, between which they are fixed. When one side of the 

 blocks is thus shaped, all the ten are, by an instantaneous movement, 

 turned a quarter round, so as to expose another side to the gouge, which 

 shapes them as before; and in this way the third and fourth sides are 

 formed of the proper shape. Three of these engines are used for blocks 

 of different sizes. 



The blocks are now taken to the scoring engine, which is intended to 

 form the score or groove round the largest diameter, for the reception of 

 the ropes or straps of the blocks. By the above machines the shells of 

 the blocks are formed. The next part of the operation is the formation 

 of the sheaves, which are made of lignum vitae. By means of two saws, 

 the straight saw and the circular saw, the tree of lignum vitae is cut into 

 pieces approaching to a circular shape, and nearly of the intended 

 sheave. These pieces are taken to the crown or trepan-saw, with a 

 centre bit in its axis. When the wood is properly fixed, the saw is 

 applied against it, and cuts it into a circular form with great rapidity, 

 while it, at the same time, forms a hole exactly in the centre. 



The sheaves are now taken to the coaking engine ; a machine of 

 splendid ingenuity. It is employed to form in the centre of the sheave 

 a cavity of the shape of three small semicircles, arranged at equal 

 intervals round the centre hole formed by the crown saw. This cavity 

 is intended for the reception of the coak or metal bush, which is made 

 of copper, zinc and tin, and cast of the same shape as the cavity now 

 formed. When the coaks are inserted into the sheave, the drilling 

 machine is employed to perforate the three semicircular projections of 

 the coaks and the wood beneath, in order to fasten the coaks by copper 

 pins put in these holes. The pins being placed* into the holes, then 

 drilled, are rivetted by means of the rivetting hammers, which are made 

 to strike a heavier blow at the end of the operation. The sheave is now 

 carried to the broaching engine, and fixed to an axis revolving vertically. 

 A broach or cutter is inserted in the hole in the centre of the coak, for the 



