No. 9. The scoring engine forms the scoring of the blocks, which is a groove round its largest dia meter, for the reception of the strap of the block. This groove is shallow, where it passes over the ends of the pin of the block, and at one end ; but at the other end, it is of considerable depth. Only two of the scoring engines are required, as they will admit a great latitude of different sizes, and they perform so quickly, as to score all the blocks made by the other machines.
The foregoing machines are appropriated to the formation of the shells of the blocks. Afterwards they are trimmed, polished, and finished by hand, as the surfaces are somewhat rough, though exactly the true shape and size ; and this is almost as expensive an operation as any of the preceding, not because the blocks require much to be taken off to make them smooth, but because this process cannot derive any assistance from machinery, while the expense of la bour in the maciLle work is so exceedingly small.
We now come to enumerate those machines em ployed for making the sheaves. The wood for these is cut from a tree of lignum vita, across the grain, so as to form pieces approaching to a circular figure, and nearly the thickness of the intended sheave. These pieces are cut by two machines. The first of these, No. 10. The straight saw, for converting the lig num vita. This is constantly moving backwards and forwards by the machinery, in a horizontal plane. The tree of lignum vita is fixed vertically, and raised so much above the plane of the saw as the thickness of the intended sheave ; and the saw being applied to the wood, quickly cuts it through, separating a piece from the end of the tree, just the true thick ness to form the sheave. This saw is appropriated to cutting out the largest sheaves, because the circu lar saw, to be next mentioned, would not act freely through a large and hard substance.
No. 11. Thecircular sate is for the same purpose, but is applied to the smaller sheaves. The tree is, as in the former instance, fixed in a vertical position, but upon the end of a spindle, in such a manner that it can re volve upon its own axis, and the circular saw has its axis placed vertically, and mounted in a frame which moves upon a centre,*so that the saw moves in an arc of a circle, but still continues in the same plane. The saw, as it revolves, is applied against the tree, by mo ving it in its arc, and cuts off a thin plate. These plates are now sorted out as to the sized sheave which each will make with the least waste : They are then carried to, No. 12. The crown saw. This is a saw similar to
a trepan, and having a centre bit in the axis of it. The piece of wood being fixed by a neat contrivance before this saw, it is applied against the wood, and quickly cuts out a circle, and at the same time forms the centre hole, exactly in the centre of it.
No. 13. The coaking engine is perhaps the most ingenious of all these machines. It forms, by means which we cannot describe without the drawing, the cavity in the centre of the sheave for the reception of the cock or metal bush. This cavity is in the form of three small semicircles, arranged at equal intervals round the circular holes formed in the last machine. Two of these engines are used. The sheaves arc cut by this engine, first on one side for one of the coaks, and they are then turned to have the other cut. The coaks are now inserted into the cavities cut by the coaking engines. They are cast of a mixture of copper, zinc, and tin, called gun metal, to the true shape at once, by means of an accurate pattern moulded in sand.
No. let. The drilling machine is applied to perfo rate the three semicircular projections of the coaks ; at. the same time it drills through both the coaks and the wood of the sheave. The copper pins, which are put into these holes, arc cut from the proper sized wire, by a simple tool fixed in the vice, all the same .length. The pins being inserted into the holes, are carried to, No. 15. The rivetting hammers, two small tilt hammers put in rapid motion by the machinery, for the purpose of rivetting the spins which hold the gun B] metal coaks into the cavity in the sheaves, made by the coaking engines. These hammers, also, by pres sing on a treddle, can strike a heavier blow towards the end of the operation. The sheaves in this state are carried to, No. 16. The broaching engines, of which three are used. The sheave is fixed to a vertical revolving axis, and the borer is brought down into the hole in the centre of the cocked sheave, and broaches it out to•a perfect cylinder. The sheaves thus formed, re quire only to be turned in, No. 17. The face turning lathe. This is an ex cellent lathe, provided with a sliding rest, which sup ports the turning tool, and moves it slowly across the face of the sheave, which is fixed upon the end of the spindle or mandrel of the lathe, and turned round thereby.