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. 830. Another arrangement for a water-wheel governor. In this the governor controls the shuttle or gate by means of the cranked lever, which acts on the strap or belt in the following manner: - The belt runs on 1 of 3 pulleys, the middle one of which is loose on the governor spindle, and the upper and lower ones fast. When the governor is running at the proper speed the belt is on the loose pulley, as shown; but when the speed increases, the belt is thrown on the lower pulley, and thereby caused to act upon suitable gearing for raising the gate or shuttle and decreasing the supply of water. A reduction of the speed of the governor brings the belt on the upper pulley, which acts upon gearing for producing an opposite effect on the shuttle or gate.
Fig. 831. A knee-lever, differing slightly from the toggle-joint shown in Fig. 811. It is often used for presses and stamps, as a great force can be obtained by it. The action is by raising or lowering the horizontal lever.
Fig. 832. Circular into rectilinear motion. The waved wheel, or cam, on the upright shaft communicates a rectilinear motion to the upright bar through the oscillating rod.
Fig. 833. A drum, or cylinder, having an endless spiral groove extending all around it, one half of the groove having its pitch in one, and the other half its pitch in the opposite direction. A stud on a reciprocating rectilinearly-moving rod works in the groove, and so converts reciprocating into rotary motion. This has been used as a substitute for the crank in a steam engine, and as a means of transmitting motion in Foster's pressure gauge.
Fig. 834. The rotation of the disc carrying the crank-pin gives a to-and-fro motion to the connecting rod, and the slot allows the rod to remain at rest at the termination of each stroke. It has been used in a brick press, in which the connecting rod draws a mould backward and forward, and permits it to rest at the termination of each stroke, that the clay may be deposited in it and the brick extracted.
Fig. 835. The slotted crank at the left hand of the figure is on the main shaft of an engine, and the pitman which connects it with the reciprocating moving power is furnished with a pin which works in the slot of the crank. Intermediate between the first crank and the moving power is a shaft carrying a second crank, of an invariable radius, connected with the same pitman. While the first crank moves in a circular orbit, the pin at the end of the pitman is compelled to move in an elliptical orbit, thus increasing the leverage of the main crank at those points which are most favourable for the transmission of power.
Fig. 836. A modification of Fig. 835, in which a link is used to connect the pitman with the main crank, thereby dispensing with the slot in the crank.
Fig. 837. Another form of steam-engine governor. Instead of the arms being connected with a slide working on a spindle, they cross each other, and are elongated upward beyond the top, and connected with the valve-rod by 2 short links.
Fig. 838. Valve-motion and reversing gear, used in oscillating marine engines. The two eccentric-rods give an oscillating motion to the slotted link, which works the curved slide over the trunnion. Within the slot in the curved slide is a pin attached to the arm of a rock-shaft, which gives motion to the valve. The curve of the slot in the slide is an are of a circle, described from the centre of the trunnion, and as it moves with the cylinder it does not interfere with the stroke of the valve. The 2 eccentrics and links are like those of the link-motion used in locomotives.
Fig. 839. A mode of obtaining an egg-shaped elliptical movement.
Fig. 840. A movement used in silk machinery for the same purpose as that described in Fig. 812. On the back of a disc or bevel-gear is secured a screw, with a tappet-wheel at one extremity. On each revolution of the disc the tappet-wheel comes in contact with a pin or tappet, and thus receives an intermittent rotary movement. A wrist, secured to a nut on the screw, enters and works in a slotted bar at the end of the rod, which guides the silk on the bobbins. Each revolution of the disc varies the length of stroke of the guide-rod, as the tappet-wheel on the end of the screw turns the screw with it, and the position of the nut on the screw is therefore changed.
Fig. 842. A means of giving one complete revolution to the crank of an engine to each stroke of the piston.
Figs. 843, 844. Contrivance for uncoupling engines. The wrist, which is fixed on one arm of the crank, not shown, will cummunicate motion to the arm of the crank which is represented, when the ring on the latter has its slot in the position shown in Fig. 843. But when the ring is turned to bring the slot in the position shown in Fig. 844, the wrist passes through the slot, without turning the crank to which the ring is attached.
Fig. 845. Contrivance for varying the speed of the slide carrying the cutting tool in slotting and shaping machines. The driving shaft works through an opening in a fixed disc, in which is a circular slot. At the end of the shaft is a slotted crank. A slide fits in the slot of the crank and in the circular slot; and to the outward extremity of this slide is attached the connecting rod which works the slide carrying the cutting tool. When the driving shaft rotates, the crank is carried round, and the slide carrying the end of the connecting rod is guided by the circular slot, which is placed eccentrically to the shaft; therefore, as the slide approaches the bottom the length of the crank is shortened, and the speed of the connecting rod is diminished.
Fig. 846. Reversing gear for a single engine. On raising the eccentric-rod, the valve-spindle is released. The engine can then be reversed by working the upright lever, after which the eccentric-rod is let down again. The eccentric in this case is loose upon the shaft, and driven by a projection on the shaft acting upon a nearly semicircular projection on the side of the eccentric, which permits the eccentric to turn half-way round on the shaft on reversing the valves.