(324) A further point requires elucidation. If the spindle blade were parallel, the number of revolutions necessary to wind the 63 inches of yarn properly, when the cop bottom is formed, being fixed, no further alteration would be necessary. But these conditions do not exist, and the nose of the cop is wound upon a continually diminishing diameter. It is of the utmost importance that the yarn is wound tightly at the nose during the whole of the building of the cop. The rate of the vertical traverse being practically uniform, unless an acceleration of the spindle velocity occurred, there would be slack winding during the latter part of the building of the cop. This would produce a sponginess of the nose, which, when the yarn was drawn off in the subsequent process of winding, as shown by the arrow in Fig. 164, would result in several rings or coils being pulled out in an entangled condition, thus producing waste. Technically the cop would be said to be “halched.” Illustrating this part of the subject by figures, if the diameter of the spindle at the point =B=, Fig. 163, be assumed to be 1/4 inch, its circumference would be ·7854 inch; while if the diameter at =H= be assumed to be 1/8 inch, the circumference would be only ·3927 inch. To wind, say, 10 inches of yarn in each case, would require about 12 and 25 revolutions of the spindle respectively. It is therefore clear that, if the same length is to be wound with equal tension upon the nose of the cop throughout the whole process of building, there must be a gradual acceleration of the terminal velocity of the spindle. Although this is only slight at first it is required at an earlier point as the cop is formed, and becomes of increasing importance.
(325) It will be shown, a little later, that the rotation of the spindles during winding is obtained by the pull of the carriage on a chain, which has its other end attached to an oscillating arm, being fastened to a drum on the carriage. To get a clear idea of the action of this part of the mechanism the two diagrams shown in Figs. 166 and 167 are given, a study of which will be profitable. In Fig. 166 the circles =B C D= represent three positions of the barrel or drum after it has moved in a horizontal plane in the direction of the arrow. To the drum a chain is supposed to be attached, which is held at the point =A=. It is, of course, understood that the barrel is mounted upon a shaft or axis so that it can freely revolve. If it be now assumed that the barrel is in the left hand of the three positions =B=, the chain will be wrapped completely round it. As it is moved horizontally in the direction of the arrow it is revolved, as indicated by the curved arrows, and, by the time it has reached its middle position =C=, has been rotated sufficiently to unwind about half a turn of the chain. A further horizontal motion to the right hand position =D= will complete the unwinding, and, by this time, the drum will have made one complete revolution. It will be at once seen that the rate at which the drum will be revolved will depend upon two factors—its diameter, and the speed of its horizontal traverse. If the point =A= at which the chain is held is stationary, and the horizontal movement uniform, then the rotation of the barrel will be constant. But if the barrel be traversed at a variable rate then its rotation will also be variable. In actual practice this uniformity does not exist, for, as was shown in paragraph 315, the taking-in scrolls vary considerably in diameter. Assuming this variation to be 1:3:1, it would follow that the rotation of the barrel would increase and diminish in the same ratio. In practice this is what happens, and the speed of the revolution of the barrel is quicker about the middle of the taking-in than at any other time.