Wrapping ConnectorsBelts, Cords and Chains Flat belts of leather or of gutta percha, round cords of catgut, hemp or other material, and metal chains are used as wrapping connectors to transmit rotatory motion between pairs of pulleys and drums.
This system presents the greatest advantages in point of economy of driving power, especially where the gradients are variable, but is expensive in first cost, and is not well suited for curves, and branch roads cannot be worked continuously, as a fresh set of pulleys worked by bevel gearing is required for each branch.
Chains require pulleys or drums, grooved, notched and toothed, so as to fit the links of the chain.
Guide pulleys are set with their diametral planes in the planes containing corresponding pairs of tangents, and a continuous belt wrapped round these pulleys in due order can then be run in either direction.
Wheels creak on their axles as the cogs engage one another and the revolving pulleys whirr with the rapidity of their movement, but a neighboring wheel is as quiet and motionless as though it were prepared to remain so for a hundred years; but the moment comes when the lever catches it and obeying the impulse that wheel begins to creak and joins in the common motion the result and aim of which are beyond its ken.
Benjamin (American Machinist, 1898) on castiron pulleys loaded by a belt to imitate the conditions in practice led him to the conclusion that the rim is usually not sufficiently rigid to load the arms equally, and that the ends of the arms are subjected to bending movements of opposite sign, that at the nave being almost invariably the greater.
Just as in a clock, the result of the complicated motion of innumerable wheels and pulleys is merely a slow and regular movement of the hands which show the time, so the result of all the complicated human activities of 160,000 Russians and French--all their passions, desires, remorse, humiliations, sufferings, outbursts of pride, fear, and enthusiasm--was only the loss of the battle of Austerlitz, the so-called battle of the three Emperors--that is to say, a slow movement of the hand on the dial of human history.
When the poise is at the zero end, and there is no load on the platform, the end of the steelyard is down, and has locked the ratchet wheel by means of the pawl; the shaft being thus locked, the sprocket wheels are stopped, the drum-shaft runs free by the friction clutch, and the two pulleys which are connected by the crossed band are running idle.
Wooden pulleys are preferably made of maple, the rim being formed of small sections morticed, pinned and glued together, with the grain set in such directions that any warping of the material will leave the cylindrical form practically unaltered.
Wooden pulleys are generally made in two halves, bolted together at the rim and nave, and are provided with wooden spokes dovetailed into the rim and secured by keys.