Discoveries and Inventions of the Nineteenth Century

frame, b, which is connected with the former, is a small disc wheel, a, having precisely the same radius as that of the circle traced out by the cutters, and this disc is made by a strong spring to press against the pattern. The cutters, being fixed in the same rocking-frame which carries this guiding-wheel, must partake of all its backward and forward motions, and as the cutting-wheel and the guide-wheel are so arranged as to have always the same relative positions to the axes of the two headstocks, it follows that the edges of the cutters will trace out identically the same form as the circumference of the guiding-disc. The latter is, of course, not driven round, but simply turns slowly with the pattern by friction, for it is pressed firmly against the pattern by a spring or weight acting on the frame, in order that the cutters may be steadily maintained in their true, but ever-varying, position. The rocking-frame receives a slow longitudinal motion by means of the screw, n, so that the cutters are carried along the work, and the guide along the pattern. The whole arrangement is self-acting, so that when once the pattern and the rough block of wood have been fixed in their positions, the machine completes the work, and produces an exact repetition of the shape of the pattern. It is plain that any kind of forms can be easily cut by this lathe, the only condition being that the surface of the pattern must not present any re-entering portions which the edge of the guide-wheel cannot follow. The machine is largely used for the purposes named above, and also for the manufacture of the spokes of carriage-wheels. The limits of this article will not permit of a description of the beautiful adjustments given to the mechanism in the example before us, particularly in the arrangement for driving the cutters in a framework combining lateral and longitudinal motions; but the intelligent reader may gather some hints of these by a careful inspection of the figure. The machine is sometimes made with the frame carrying the guide-wheel and cutters, not rocking but sliding in a direction transverse to the axes of the headstocks. It is extremely interesting to see the Blanchard lathe at work, and observe how perfectly and rapidly the curves and form of the patterns seem to grow, as it were, out of the rudely-shaped piece of wood, which, of course, contains a large excess of material, or, in the picturesque and expressive phrase of the workmen, always gives the machine something to eat. 98 Fig. 36.—Vertical Saw. SAWING MACHINES. With the exception of the last, all the machines hitherto described in the present article are distinguished by this—they are tools which are used to produce other machines of every kind. Without such implements it would be impossible to fashion the machines which are made to serve so many different ends. Another peculiarity of these tools has also been referred to, namely, that they are especially serviceable, and indeed essential, for the reproduction of others of the same class. Thus, the accurate leading-screw of the lathe is the means used to cut other accurate screws, which shall in their turn become the leading-screws of other lathes, and a lathe which forms a truly circular figure is a necessary implement for the construction of another lathe which shall also produce truly circular figures. In these tools, therefore, we find the copying principle, to which allusion has been already made, as the great feature of all machines; but in order to bring this principle still more clearly before the reader, we have described in the Blanchard Lathe a machine of a somewhat different class, because it embodied a very striking illustration of the principle in question. We are far from having described all the implements of the mechanical engineer, or even all the more interesting ones; for example, we have given no account of the powerful lathes in which great masses of iron are turned, or of the analogous machines, which, with so much accuracy, shape the internal surfaces of the cylinders of steam engines, of cannons, &c. The 99history of the steam engine tells us of the difficulties which Watt had to contend with in the construction of his cylinders, for no machine at that time existed capable of boring them with an approach to the precision which is now obtained. Fig. 37.—Circular Saw. The kind of general interest which attaches to the tools we have already described is not wanting in yet another class of machine-tools, namely, those employed in converting timber into the forms required to adapt it for the uses to which it is so extensively applied. And for popular illustration, this class of tools presents the special advantage of being readily understood as regards their purpose and mode of action, while their simplicity in these respects does not prevent them from showing the advantages of machine over hand labour. Everybody is familiar with the up-and-down movement of a common saw, and in the machine for sawing balks of timber into planks, represented in Fig. 36, this reciprocating motion is retained, but there are a number of saws fixed parallel to each other in a strong frame, at a distance corresponding to the thickness of the planks. The saws are not placed with their cutting edges quite upright, but these are a little more forward at the top, so that as they descend they cut into the wood, but move upwards without cutting, for the teeth then recede from the line of the previous cut, while in the meantime the balk is pushed forward ready for the next descent of the saw-frame. This pushing forward, or feeding, of the timber is accomplished by means of ratchet-wheels, which are made to revolve through a certain space after each descent of the saw-frame, and, by turning certain pinions, move forward the carriage on which the piece of timber is firmly fixed, so that when the blades 100of the saws are beginning the next descent they are already in contact with the edge of the former cut. To prevent the blades from moving with injurious friction in the saw-cuts, these last are made of somewhat greater width than the thickness of the blades, by the simple plan of bending the teeth a little on one side and on the other alternately. The rapidity with which the machine works, depends of course on the kind of wood operated upon, but it is not unusual for such a machine to make more than a hundred cuts in the minute. The figure shows the machine as deriving its motion by means of a strap passing over a drum, from shafting driven by a steam engine. This is the usual plan, but sometimes the steam power is applied directly, by fixing the piston-rod of a steam cylinder to the top of the saw-frame, and equalizing the motion by a fly-wheel on a shaft, turned by a crank and connecting-rod. A very effective machine for cutting pieces of wood of moderate dimensions is the Circular Saw, represented in Fig. 37. Here there is a steel disc, having its rim formed into teeth; and the disc is made to revolve with very great speed, in some cases making as many as five hundred turns in a minute, or more than eight in a second. On the bench is an adjustable straight guide, or fence, and when this has been fixed, the workman has only to press the piece of wood against it, and push the wood at the same time towards the saw, which cuts it at a very rapid rate. Sometimes the circular saw is provided with apparatus by which the machine itself pushes the wood forwards, and the only attention required from the workman is the fixing of the wood upon the bench, and the setting of the machine in gear with the driving-shaft. Similar saws are used for squaring the ends of the iron rails for railways, two circular saws being fixed upon one axle at a distance apart equal to the length of the rails. The axle is driven at the rate of about 900 turns per minute, and the iron rail is brought up parallel to the axle, being mounted on a carriage, and still red hot, when the two ends are cut at the same time by the circular saws, the lower parts of which dip into troughs of water to keep them cool. Fig. 38.—Pit-Saw. 101 Fig. 39.—Box Tunnel. RAILWAYS. Fig. 40.—Coal-pit, Salop. Towards the end of last century, tramways formed by laying down narrow plates of iron, were in use at mines and collieries in several parts of England. These plates had usually a projection or flange on the inner edge, thus—L, in order to keep the waggons on the track, for the wheels themselves had no flange, but were of the kind used on ordinary roads. These flat tramways were found liable to become covered up with dirt and gravel, so that the benefit which ought to have been obtained from their smoothness was in a great measure lost. Edge rails were, therefore, substituted, and the wheels were kept on the rails by having a flange cast on the inner edge of the rim. The rails were then always made of cast iron, for, although they were very liable to break, the great cost of making them of wrought iron prevented that material from being used until 1820, when the method of forming rails of malleable iron by rolling came into use. The first time a tramway was used for the conveyance of passengers was in 1825, when the Stockton and Darlington Railway was opened—a length of thirty-seven miles. It appears that the carriages were at first drawn by horses, although locomotives were used on this and other colliery lines for dragging, at a slow rate, trains of mineral waggons. At that time engineers were exercising their ingenuity in overcoming a difficulty which never existed by devising plans for giving tractive power to the locomotive through the instrumentality of rack-work rails. It never occurred to them to first try whether the adhesion of the smooth wheel to the smooth rail was not sufficient for the purpose. During the first quarter of the present 102century the greater part of the goods and much passenger traffic was monopolized by the canals. It is quoted, as a proof of the careless manner in which this service was performed, that the transport of bales of cotton from Liverpool to Manchester sometimes occupied twice the length of time required in their voyage across the Atlantic. When an Act of Parliament authorizing the construction of a railway between Liverpool and Manchester was applied for, the canal companies succeeded in retarding, by their influence, the passing of that Act for two years. It was passed, however, in 1828, and the construction of the line was proceeded with. This line was at first intended only for the conveyance of goods, especially of cotton and cotton manufactures, and the waggons were to be drawn by horses. When the line was nearly finished the idea of employing horses was, at the instigation of Mr. George Stephenson, abandoned in favour of steam power. The directors were divided in opinion as to whether the carriage should be dragged by ropes wound on large drums by stationary engines, or whether locomotives should be employed. Finally, the latter plan was adopted, and it was also suggested that passengers might be carried. The directors offered a prize for the best locomotive, and the result has been already mentioned. In the light of our experience since that time, it is curious to read of the doubts then entertained by skilful engineers about the success of the locomotive. In a serious treatise on the subject, one eminent authority hoped “that he might not be confounded with those hot-brained enthusiasts who maintained the possibility of carriages being driven by a steam engine on a railway at