FIG. 4.
FIG. 5.
Scarcely any kind of machinery can be constructed without wheels of some kind—they serve almost numberless purposes. The fly-wheel ([fig. 1]) serves to produce a continuous motion, from its size and weight giving it a tendency to go on, and in this way causing it to fill up the intervals of unequal action, as in the ascent and descent of the piston in a steam-engine. The toothed-wheel serves to give motion to other wheels, and this at a certain rate either greater or less than its own, according to its size, and consequently the number of its teeth; thus a wheel with a hundred “cogs” or teeth united to one with but fifty, causes this to go round twice while the larger one passes round but once; but a large wheel turned round by a small one, although it moves more slowly yet does so with increased power just in proportion to its slowness ([fig. 2]). The bevel-wheel ([fig. 3]) is used to change the direction of a shaft, and for all the other purposes of a toothed-wheel, from which it differs only in the position of the teeth or cogs. Wheels are sometimes made to answer the purposes of bevel wheels, by having the cogs on the surface of the one wheel, and the other as an ordinary toothed-wheel ([fig. 4]). The ratchet-wheel ([fig. 5]) is a wheel with its teeth pointing in one direction like the teeth of a saw, and into which a tongue of iron is made to fall, so that the wheel can only be turned in one direction. These wheels are used where the machinery is liable to run back if left, as in the “crane,” &c. The capstan ([fig. 6]) is a kind of ratchet wheel, and is so made that long spokes may be placed in the holes, to be moved round by men, and taken away when out of use; it is a very powerful piece of machinery, and is used for “weighing anchor” (see “[Anchors]”). The pulley ([fig. 7]) is a series of wheels used to increase power by diminishing the rate of movement; they are much used in the rigging of ships, and are then called “blocks.” There are different ways of connecting wheels so as to communicate the motion of one to another; they may be toothed as before described, or a “lathe-band” may be passed over them. This may be either round or cord-like, and made of cat-gut, or flat and made of leather or gutta-percha. This mode of producing motion is very useful where evenness and smoothness of action are required, or where the wheels are at a considerable distance apart; they have their ends united so as to form a ring, or endless band, and are sometimes used to communicate motion to a great many wheels, as seen in [fig. 8]. The eccentric-wheel has its axis out of the centre; it is used for the same purpose as a crank, but the action is more continuous and even. While the crank is most frequently used to produce a circular or rotatory motion from an up-and-down motion, the eccentric-wheel is more commonly used to produce an up-and-down motion from a rotatory one ([fig. 9]). Wheels take almost every variety of form, and are not, in some cases, even round; in winding yarn on to bobbins, where a motion is required of a constantly varying rate, two elliptical wheels are made to act on each other, the end of one being approximated to the centre of the long axis of the other, ([fig. 10]).
FIG. 9.
FIG. 10.
Wheels for carriages are used to diminish friction, by causing the “tire” or smooth outer edge to roll upon the surface instead of being rubbed; all the friction in wheels is in the centre or axle, which being turned smooth, and greased or oiled, works very easily. Carriage wheels are made to revolve upon a fixed axle, and each wheel revolves independently of the other, but in railway-carriages and engines, the wheels are united in pairs, and the axle revolves with them, the weight being borne outside of the wheel on a small part of the axle which projects. The various parts of a wheel are the box or “nave” which is the centre part, the “spokes” or those bars which connect it with the centre edge or felloes, and the “tire,” an iron band binding the whole together. Wheels for gun-carriages are made at Woolwich Arsenal by machinery. The following is a description of them, taken from the “Times” newspaper:—