Ropes formed by plaiting instead of twisting are made use of for some purposes in which pliability is especially needed ; they being more stipple and less liable to entanglement than those of the ordinary make. Such ropes are preferred for sash-lines, clock-lines, &c., and generally where the rope has to pass over pulleys of small diameter.
Originally all the yarns composing a strand were selected of the same length. This arrangement was defective, as it is evident that when a number of yarns are stretched at length in a cylindrical mass, they will lie at different distances from the centre of the cylinder; so that, when twisted together, as all the yarns must form spirals of the same number of turns, those which are near the outside, forming spirals of large diameter, will be stretched to their full extent; while those near the centre, forming spirals of smaller diameter, will be less shortened by the process of twisting, and must therefore be more or less puckered up, according to their proximity to the centre of the mass. The first successful attempt to remedy this defect by varying the length of the yarns according to their position in the strand, was that under Captain Huddart's patent of 1793 ; since which time many further improvements have been effected in this essential point.
This brings us to notice briefly the application of machinery to rope making, which may be said to have begun about the year 1783, and to have been the subject of numerous ingenious inventions since that date. One series of machines relates to the combining of the hempeu fibres into yarns ; another to the twisting of yarns into ropes ; while the more complex kinds include both of these actions. Mr. Lang, of Greenock, was the first to produce successfully machine-spun yarns, intended to get rid of the irregularities and defects of those formed by hand. By his process the hemp is more completely heckled, or divided into fibres, than in the common mode of proceeding; and the advantage of cash fibre being Laid at full length in the yarn, instead of being doubled, as in hand-spinning, is ensured. By a modification of the usual process, the fibres of hand-spun yarns may be laid in at full length, instead of being doubled, as when they enter the yarn by their bight ; but experiment has not shown any great. advantage from such a mode of spinning. That some improvement in this operation was needful, may be inferred from the result of a comparison between Mr. Lang's machiue-spuu yarns and those of equal grist spun by hand ; the result showing the strength of the former to exceed the latter by fifty-five per cent. Mr. Sherman, of Liverpool, patented a method of
rope-making intended to obviate the necessity for a long shed or rope walk. The machinery comprises rotating tables with hollow shafts or axes; spindles project from the surface]; of the tables; bobbins are mounted on the spindles; and hemp is wound on the bobbins. The number of bobbins depends on the number of yarns and strands. The ends of the yarns are passed through holes in a draw-plate beyond the hollow shaft of one table, then through tho hollow shaft, then through another shaft ; and so on. The yarn from each bobbin thus becomes twisted round that of the other bobbins on the same table; then round the similarly twisted strands of another series ; and then of a third. The finished strand or rope is drawn from the tube of the last table, and is wound upou a reel ready for use. A modification of this planetary system, as the inveutor calls it, suffices for twisting the strands into a rope.
Captain Huddart's rope-making machinery, above adverted to, is very ingenious. In order to get rid of the unequal strain upon the exterior and interior of a rope, I luddart saw that the outer yarns of every strand ought to be somewhat longer than the inner, to com pensate for the greater circumference round which they have to turn. This lie accomplished in a beautiful way. Bobbins are arranged in a skeleton frame, each poised on a pivot and loaded with yarn ; the number of bobbins depends on the thickness of the strands to be made. The ends of all the yarns are passed through an equal number of small holes in a plate, and combined into one close group, which is slightly compressed by passing through a tube, and then wound on a reel. The mechanism between the plate and the reel rotates on a horizontal axis, thereby imparting a twist to the assemblage of yarns. The free rotation of the bobbins, the arrangement of the holes in the plate, the position of the tube, and the velocity of revolution—all combine to produce a strand of any desired hardness of twist, without undue strain upon any of the yarns. The strand thus produced is a smooth uniform piece of cordage, varying in thickness according to the size of the rope to be made ; for a 12-inch cable, the strand is about an inch thick and contains 80 yarns. Being worked by steam power and having facilities for renewing the bobbins as they are exhausted, this machine can produce a rope any length.