WHEEL WORK, in machinery, con sists of a combination of wheels commu nicating motion to one another. Such combinations may be formed in various ways ; but they are generally reducible to the principle of the wheel and axle, though the wheel, which turns the other, is not usually on the same axis with it. The motion in such cases is communi cated from the one wheel to the other, either by belts or straps passing over the circumferences of both, or by teeth cut in those circumferences, and working in one another. In either of these ways the velocities of points in their circum ferences are equal ; and consequently their angular velocities, or the number of revolutions which they make in the same time, are inversely as their radii. When one wheel drives another by teeth, they necessarily turn in opposite direc tions ; if united by a cord or belt, they will turn in the same direction, if the belt does not cross itself between the two wheels ; but if the belt crosses itself, they will turn in opposite directions. The chief advantage of transmitting mo tion by cords or belts is, that the wheels may be placed at any convenient dis tance from each other, and be made to turn either in the same or in opposite directions.
Wheels may act on one another, so as to communicate motion in various ways. When the resistance of the work is not great, the object may he accomplished by the mere friction of their circumfer ences. In order to increase the friction, the surfiees of the rims are faced with buff leather (caoutchouc might answer the purpose better), or wood cut against the grain, andpressed together with a certain degree ofr force. This method is sometimes used in spinning machinery, and has even been applied successfully to the saw-mill ; but it is seldom adopted in works on a great scale. Motion commu nicated in this manner proceeds smooth ly and evenly, and is accompanied with little noise.
When motion is to be transmitted through a train of wheel work, toothed wheels are generally employed. It is
usual to call a small wheel acted on by a large one opinion, and its teeth the leaves of the pinion. Wheels and pinions are combined variously, sometimes as in the annexed cut ; at other times, the axle of the wheel, which bears the power, is a pinion, which drives the second wheel. The axle of this wheel carries a pinion, which drives the third wheel. When motion is communicated in this manner, the angular velocity of the first wheel is to that of the last pinion as the product formed by multiplying together the radii of all the wheels to the product formed by multiplying together the radii of all the pinions. Consequently, if R, R', R", &c., denote respectively the radii of the wheels, and r, r' r", &c., the radii of the pinions, we shall have, by the principle of virtual velocities p (R. X R' x R'', &c.) (r x rl X r", &c.) As the size of the teeth of any wheel and the pinion into which it works must be equal, we may substitute for the radii the number of teeth in the wheels and pinions respec tively.
Toothed wheels, as distinguished by the position of the teeth relatively to the axis, are of three kinds : spur wheels, crown wheels, and bevelled wheels. When the teeth are raised upon the edge of the wheel, or are perpendicular to the axis (as in the above figure), the wheel is a spur wheel ; when they are raised parallel to the axis, or perpendicular to the plane of a wheel, it is a crown wheel ; and when they are raised on a surface inclined to the plane of the wheel, it is called a bevelled wheel. The combination of a crown wheel with a spur wheel as pinion is used when it is required to communi cate motion round one axis to another at right angles to it. Two bevelled wheels are employed to transmit motion from one axis to another inclined to it at any proposed angle. Wheels have also dif ferent names, according to their mode of action, as heart wheel, sun-and-planet wheel.