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Crane

wheel, axis, levers, machine, wheels and chain

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CRANE. A machine employed at wharfs, warehouses, &c. for and lowering goods ; it consists of a long projecting arm, called the jib, having a pulley at the outer end, over which passes the rope or chain by which the goods are raised, the other end of the rope being wound round a barrel either attached to the foot of the jib, or plamd at any convenient distance from it. Various modes have been resorted to for turning the chain barrel ; on piers and jetties it is frequently placed erect, and worked like a capstan : another method which was formerly very common, but is now little used, was to place it horizontally, and connect it with the axis of a large hollow drum, within which were placed i a number of men, who, by stepping upon battens nailed upon the interior circumference parallel to the axis, caused the drum to revolve. But the moat effective and best mode of employing the strength of men in working cranes (in situations which will admit of its application), is that invented and patented by Mr. Hardy : as in the preceding plan, the chain barrel is connected with a large drum fixed upon a horizontal axis, but the steps upon which the labourers tread are ranged upon the outside (instead of the inside) of the drum, radiating like the floats of an undershot water-wheel, and the labourers continually step upon that arm or step which is horizontal, so as always to act upon the longest lever. One or more of these cranes were erected at the East India Warehouses, and the principle has been since rendered familiar to one very numerous portion of the public by the invention ascribed to Mr. Cubitt, of Ipswich,— called the treadmill.

The preceding figure represents a side elevation of Mr. L. Wright's patent crane, erected at the West India Docks, and which was the subject of much acrimonious controversy amongst some of the scientific periodicals of the time. a is the principal wheel, fixed to and revolving with the chain barrel b on the axis c; the periphery of the wheel c is made perfectly flat on both sides, for the reception of the numerous small wheels ei, alternately placed on the opposite sides of the ring, with their axes fixed into it; these, which may be called friction wheels, are solid, about an inch thick, and five inches in diameter— they are turned smooth, and made bright in all parts ; e e are two (of four) levers, worked by a four-throw crank f f turned by the winches g g ; the levers pass between guides at o, and slide over rollers at p, which form the fulcrum of the levers; and by the revolutions of the cranks the levers are successively projected against the under sides of the small wheels d, from whence they are, by the continued revolution of the cranks, again withdrawn, and again projected under the next little wheel below the former, each wheel being raised by the angular motion of the lever over which it rolls. It should be observed that only

one side or half of the machine is seen, the other side being a duplicate of it, having two similar levers, large wheel, and smaller wheels, &c. The machine (as delineated) is in gear; to put it out of gear a locking bar t is lifted, and thrown into the position shown by the dotted lines ; then the framing r which carries the crank, inclined planes, and fly-wheel, and turns upon the centre s, is thrown back, by which the axis of the crank moves in the arc of a circle (shown by dots) to the position n. What mechanical advantage the inventor expected to obtain by this singular construction, it is hard to say ; the machine is cumbersome and unsightly, has a complication of parts, in which the friction far exceeds that of a well-made crane of the common construction, to which it is also decidedly inferior in the circumstance of affording no means of altering the power or velocity according to the weight to be raised. The method adopted by the inventor for putting the machine in and out of gear is also very defective; but if the crane offered any advantages in other respects, this latter defect might be obviated.

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