This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
Fig. 1170. Irregular circular motion imparted to wheel A. C is an elliptical spur-gear rotating round centre D, and is the driver. B is a small pinion with teeth of the same pitch, gearing with C. The centre of this pinion is not fixed, but is carried by an arm or frame which vibrates on a centre A, so that as C revolves the frame rises and falls to enable pinion to remain in gear with it, notwithstanding the variation in its radius of contact. To keep the teeth of C and B in gear to a proper depth, and prevent them from riding over each other, wheel 0 has attached to it a plate which extends beyond it and is furnished with a groove g h of similar elliptical form, for the reception of a pin or small roller attached to the vibrating arm concentric with pinion B.
Fig. 1171. If for the eccentric wheel described in the last figure on ordinary spur-gear moving on an eccentric centre of motion be substituted, a simple link connecting the centre of the wheel with that of the pinion with which it gears will maintain proper pitching of teeth in a more simple manner than the groove.
Fig. 1172. This movement is designed to double the speed by gears of equal diameters and numbers of teeth - a result once generally supposed to be impossible. Six bevel-gears are employed. The gear on the shaft B is in gear with two others-one on the shaft F, and the other on the same hollow shaft with C, which turns loosely on F. The gear D is carried by the frame A, which, being fast on the shaft F, is made to rotate, and therefore takes round D with it. E is loose on the shaft F, and gears with D. Now, suppose the two gears on the hollow shaft C were removed and D prevented from turning on its axis, one revolution given to the gear on B would cause the frame A also to receive one revolution, and as this frame carries with it the gear D, gearing with E, one revolution would be imparted to E; but if the gears on the hollow shaft C were replaced D would receive also a revolution on its axis during the one revolution of B, and thus would produce two revolutions of E.
Fig. 1173. Wheel-work in the base of capstan. Thus provided, the capstan can be used as a simple or compound machine, single or triple purchase. The drumhead and barrel rotate independently; the former, being fixed on spindle, turns it round, and when locked to barrel turns it also, forming single purchase; but when unlocked wheel-work acts, and drumhead and barrel rotate in opposite directions, with velocities as three to one.
Fig. 1174. J. W. Howlett's adjustable factional gearing. This is an improvement on that shown in Fig. 1134. The upper wheel A shown in section, is composed of a rubber disc with V-edge, clamped between two metal plates. By screwing up the nut B, which holds the parts together, the rubber disc is made to expand radially, and greater tractive power may be produced between the two wheels.
Fig. 1175. Scroll-gear and sliding pinion, to produce an increasing velocity of scroll-plate A, in one direction, and a decreasing velocity when the motion is reversed. Pinion B moves on a feather on the shaft.
Fig. 1176. Entwistle's gearing. Bevel-gear A is fixed. B, gearing with A, is fitted to rotate on stud E, secured to shaft D, and it also gears with bevel-gear C loose, on the shaft D. On rotary motion being given to shaft D, the gear E revolves around A, and also rotates upon its own axis, and so acts upon C in two ways, namely, by its rotation on its own axis and by its revolution around A. With three gears of equal size, the gear C makes two revolutions for every one of the shaft D. This velocity of revolution may, however, be varied by changing the relative sizes of the gears. C is represented with an attached drum C. This gearing may be used for steering apparatus, driving screw-propellers, etc. By applying power to C action may be reversed, and a slow motion of D obtained.