Spiral Drums
These drums are used at some collieries for drawing coal from the mines. The round wire rope is made to coil in a spiral groove upon the surface of the drum, which is formed by the frusta of two obtuse cone-castings, joined together with their small ends outwards, the idea being to equalize the work of the winding-engine throughout the journey; for when the load is greatest, with the load at the bottom and all the rope out, the duty imposed upon the engine is limited to the length of the drum's least circumference.
There are many ingenious devices for moulding and forming the grooves in these drums; and, besides those employed in Europe, we may mention those by S. B. Whitney, Pottsville, Pa., and P. S. Dingey, author of "Machinery Pattern-making," Chicago, Ill. While the several mechanical contrivances for regulating pitch, etc., may differ in some minor details, the general principles are about the same in all. Mr. Dingey's invention consists substantially of a foot step, in which a fixed spindle is inserted vertically; the former or sweep is made to travel up and down a screw by pulling round the upper arm, the screw itself being inclined at the required angle. A bevel-gear is made fast to the spindle at the lower end, and the bracket which carries the pinion-shaft works loose upon the spindle. One end of the pinion-shaft is carried by a T-piece that turns on the spindle also, and the other end engages the working-screw by means of a universal joint, the screw itself being carried by adjustable arms at the top and bottom. The nut is prevented from turning on the screw by allowing it to work freely up and down a guide-shaft secured to the upper and lower arms, exactly parallel with the screw itself. Motion is imparted to the apparatus by drawing the arms-around; this causes the pinion and screw to turn, thus making the sweep ascend some distance at each rotation of the arms. The gears determine the pitch of the groove, and different-sized ones can be applied to suit. By simply changing the bevel-wheel and locating the pinion on opposite sides, a left or right-hand groove is produced, and, being operated by a universal joint, it is easily adjusted to any angle of drum required.