CAPSTAN

( Cabestan , Fr.; Spille , Germ.) A machine whereon the cable is wound succe ively in weighing the anchor of a ve el. It is a species of wheel and axle; the axle being vertical, and pierced with holes near its top for the insertion of the ends of horizontal levers, called handspikes, which represent the wheel. These are turned by the force of men moving in a circle. The power applied to the lever is to the resistance to be overcome, (the weight of the anchor, for example,) when the forces are in equilibrio, as the radius of the cylinder round which the cable is coiled is to the circumference described by the power. It is manifest that the radius of the axle must be augmented in this computation by half the diameter of the cable, which is supposed to lie always one coil thick upon it. The force of a man, thus applied, has been commonly estimated as equal to the traction of 27 pounds hanging over a pulley. Friction being so variable a quantity in capstans, renders the exact calculation of its mechanical effect somewhat uncertain. A stout man, stationed near the bottom of the axle, holds fast the loose part of the cable, which has already made two or three turns; and, being aided by its friction upon the wood, he both prevents it from slipping backwards, and uncoils each turn as it is progre ively made. Mr. Hind marsh, master mariner of Newcastle, obtained a patent, in February, 1827, for a contrivance to enable a capstan or windla to be occasionally worked with increased mechanical advantage. With this view, he placed toothed wheel-work, partly in the drum-head of the capstan, and partly in the upper part of the barrel, upon which the cable is coiled and uncoiled in succe ive portions. The drum-head, and also the barrel, turn loosely upon a central spindle, independent of each other, and are connected together either by the toothed geer, or by bolts. On raising or withdrawing the connecting pinion from the toothed wheels, and then locking the drum-head and barrel together, the capstan works with a power equal only to that exerted by the men at the capstan-bars, as an ordinary capstan; but on lowering the pinion into geer with the wheel-work, and withdrawing the bolts which locked the drum-head to the barrel, the power exerted by the men becomes increased in proportion to the diameter and numbers of teeth in the wheels and pinions. IMG:4147767755307473660_illo0252a.png:Capstan Fig. 255. is the external appearance of this capstan. Fig. 256. a horizontal view of the toothed geer at the top of the barrel. The barrel, with the whelps a a , turns loosely upon a verticle spindle fixed into the deck of the ve el. The drum-head b also turns loosely upon the same spindle. The circular frame c c , in fig. 256. , in which the axes of the toothed wheels d d d are mounted, is fixed to the central spindle. The rim e e e , with internal teeth, is made fast to the top of the barrel; and the pinion f , which slides upon the spindle, is connected to the drum-head. When it is intended to work the capstan with ordinary power, the pinion f is raised up into the rece of the drum-head, by means of a screw g , fig. 255. , which throws it out of geer with the toothed wheels, and it is then locked up by a pin z : the bolts h h are now introduced, for the purpose of fastening the drum-head and barrel together, when it becomes an ordinary capstan. But when it is required that the same number of men shall exert a greater power, the bolts h are withdrawn, and the pinion f lowered into geer, with the toothed wheels. The rotation of the drum-head, then carrying the pinion round, causes it to drive the toothed wheels d d d ; and these working into the toothed rim e e , attached to the barrel, cause the barrel to revolve with an increased power. Thus, under particular circumstances, a smaller number of men at the capstan or windla (which is to be constructed upon the same principle) will be enabled to haul in the cable and anchor, or warp off the ve el, which is an important object to be effected. In 1819, Captain Phillips obtained a patent for certain improvements in capstans, a part of which invention is precisely the same as this in principle, though slightly varied in its adaptation. James Brown, ship-rigger, in his capstan, patented in 1833, instead of applying the moving power by handspikes, having fixed two rims of teeth round the top of the capstan, acts upon them by a rotatory worm, or pinions turned by a winch. IMG:4147767755307473660_illo0252b.png:Capstan Fig. 257. is an elevation of this capstan, and fig. 258. is a horizontal top view. a is an upright shaft, fixed firmly to the deck, serving as an axle round which the body of the capstan revolves. A frame c , fixed to the top of a stationary shaft a , above the body of the capstan, carries the driving apparatus. The upper part of the body of the capstan has a ring of oblique teeth d formed round its edge; and above this, on the top of the capstan, is a ring of bevel teeth e . A horizontal shaft f , mounted in the top frame c , has a worm or endle screw, which takes into the teeth of the ring d ; and a short axle g , having its bearings in the central shaft a , and in the frame c , carries a bevel pinion, which takes into the bevel teeth of the ring c . The bearings of the shaft f , in the top frame, are in long slots, with angular returns, something like the fastening of a bayonet, which is for the purpose of enabling the shaft to be readily lifted in and out of geer with the teeth of the ring d : the outer bearing of the axle g of the bevel pinion is also supported in the frame c , in a similar way, in order to put it in and out of geer with the teeth of the bevel ring e . A mode of shifting these is e ential; because the two toothed rings, and their driving worm and pinion, give different speeds, and, of course, cannot be both in operation at the same time. The worm of the shaft f , being placed in geer with the teeth of the ring d , on applying rotatory power thereto, by means of winches attached to the ends of the shaft, the barrel or body of the capstan will be made to revolve with a slow motion, but with great power; and thus two men at the winches will do the same work as many men with capstan bars in the ordinary way. If a quicker movement than that of the endle screw is desired, then the driving power may be applied by a winch to the axle g of the bevel pinion, that pinion being put into geer with the bevel ring e , and the endle screw withdrawn. It should, however, be here remarked, that the patentee proposes to employ two short axles g , placed opposite to each other, with bevel pinions acting in the bevel-toothed ring, though only one is shown in the figure to avoid confusion. He also contemplates a modification of the same contrivance, in which four short axles g , placed at right angles, with pinions taking into a bevel ring, may be employed, and made effective in giving rotatory motion to the barrel of a capstan by means of winches applied to the outer ends of the axle, and turned by the labour of four men. CARAT or CARACT is a weight used by goldsmiths and jewellers. See A ay and Diamond .