Crane, a machine used for raising large, stones, and other ponderous bodies. From the numerous accidents which attend the common cranes, several skilful machinists have attempted to contrive such as would be more safe, and at the same time more easy in their operations.
The first, in point of time, is that invented by the late ingenious Mr. James Ferguson ; which has three trundles, with different numbers of staves, that may be applied to the cogs of a horizontal wheel with an upright axle; round which is coiled the rope that draws up the weight. This wheel has 96 cogs, the largest trundle 24 staves ; the next 12, and the smallest 6; so that the largest revolves 4 times for one revolution of the wheel; the next 8 ; and the smallest i.6. A winch is occasionally fixed on the axis of either of these trundles, for turning it, in proportion to the weight intended to be drawn up. While this is raising, the ratch-teeth of a wheel slip round below a catch, that falls into them, prevents the crane from turning backwards, and detains the weight in any part of its ascent, if the man who works at the winch, should accidentally quit his hold, or wish to rest himself, before the weight is completely raised.
The second, is that invented by Mr. Abraham Andrews, of Higham Ferrers, Northamptonshire. This machine weighs the body suspended, while it is rais-ing ; an improvement for which the Society for the Encouragement of Arts, etc. in 1791, granted him a premium of 15 guineas.
The proportion of the beam in theannexed plate (Fig. l.) is as1 to 20, the large weight being 5 pounds, and the smaller 1/4| of a pound. The latter, when fixed on the beam-end, will equi-poise the former, if hung on the pulley at the end of the gib-beam, which should be placed in a right line with the crane, at the time the weight is adjusted; otherwise it will occasion a friction that may prevent the moveable beam from playing freely.
Description of Mr. A. Andrews's
Crane in the annexed Engraving,
The gib of the crane stands on a horizontal beam, moveable on a centre, at A: and the distance of the centre A, from the bearing of the upright, being to the distance B, in the proportion of 1 to 20, the weight placed at B, determines that of the body suspended in the same proportion. - C is a stub, or piece of wood, which projects from the weight hanging at the end of the gib, and serves to prevent the beam from rising to too great a height.
One of the latest improvements in this useful machine, is that proposed by the Rev. E. C. in the 2d vol. of" the Repertory of Arts . and Manufactures. It consist-: simply in Introducing the action a worm, that communicates the first motion to the crane, upon the axis of the wheel in which man walks. The axis of wheel, and that of the worm, are proposed to be in separate parts, and occasionally united by a coupling-box. When goods are to be raised, the two axes should be connected; when lowered, they may be disunited, and the worm turned by a winch. Thus, the ascent, or descent, of the weight may be accelerated, or stopped, at pleasure, by the person walking on the axis of the wheel, or turning the winch; without the remotest possibility of being overpowered by the descending weight.
Explanation of the annexed Engraving, Fig. 2.
A, The wheel in which the man walks.
B, The coupling-box.
C, The worm.
D, The wheel in which it works.
E, A wheel upon the same axis, giving motion to
F, A wheel upon the axis of the windlass.
G, The winch.
This machinery (the ingenious projector adds) may be applied to a crane already erected upon the common principle. He proposes to put a wheel on anuy convenient axis in the machine, in its present state ; and, on this, a worm that may be thrown in or out of gear, at pleasure ; and to let the lever, by which it is effected, lie within the reach of the man's hand in the wheel. The goods being fastened to the crane, and raised from the floor of the warehouse, in order to be let down, the man puts the worm into gear, leaves the wheel, and causes them to descend by the winch.
These contrivances are alike eminent for their ingenuity ; and, though we do not venture to prefer either, yet we seriously recommend the adoption of some one of these improvements, as we are fully persuaded, that many fatal accidents may thus be easily avoided.