The central clutch is automatically controlled by a system of levers and two adjustable buttons with opposite bevelled faces attached to the lower stationary slide, the levers and rollers being attached to the movable slide above. As the roller touches the bevelled button it throws the lever to one side, shifting the clutch and reversing the motion of the slide. When the roller comes to the oppositely bevelled button, the clutch is thrown to the opposite side and the motion is reversed as before. Means are provided to stop the feed at any desired point. There is a connection by a light chain between the cutter-slide and the stop-shaft cam and the trip. When the slide is withdrawing the cutter and the latter is out far enough to clear the edges of the blank wheel, the chain (which is adjustable) pulls the trip and allows the stop-shaft to make a revolution, then holds it stationary until another tooth is finished, when the slide again withdraws, releases the trip again, and so on until the wheel is completely cut, when the machine rings a bell, notifying the operator that the wheel is complete. The working movements for cutting bevel-gears are the same as those described, the slides being raised to whatever incline is desired. For worm-gearing the slides are swivelled right or left, as required, in a horizontal position.
Shears and Pllnching-marbines.—Figurc a (pt. 3o) illustrates the man ner in wnich metal shears operate, a representing a piece of sheet iron and s' and s' two chisel-like tools (shear-blades), which are so forcibly moved toward each other that the edges penetrate and divide the iron. By giv ing to one blade the form of a ring (Jig. 2) and to the other that of a punch (s fitting into r) the shears become a punch and die, and the cut is circu lar. Shears are extensively used for trimming the edges of iron plates and sheets, while punching-machines serve for quickly making bolt- and rivet holes, and also for working out irregular cuts.
In the ordinary cutting-pliers, which may he considered as precursors of shears, the two chisel-like blades do not move one past the other, and, as it is possible to bring only the edges in contact, the resulting cut sur face is often somewhat uneven. In the nippers shown in Figure 5 the ordinary form is so far improved that by.an adjusting-screw placed in one of the jaws the other jaw can be advanced only sufficiently to bring the edges almost in contact, thus preventing injury to the jaws.
Shears generally have straight cutting-blades acting by rectilinear displacement (parallel shears, pt. Jig. 4; /5/. 31, figs. 4, 5; pl. 32, jigs. I, 2) or by rotation (lever shears). In the latter class two different arrangements can be made by the axis either running parallel or stand ing, vertically to the blades. For executing long cuts without interruption the blades are given the shape of circular discs, with edges sliding over each other. Such rotary or circular shears are shown in Figure 31),
in which both cutting-discs have positive motion. The blades are borne by two parallel shafts revolving in opposite directions, so that a piece of sheet iron—which must, however, not be too thick—introduced upon one side of the blades is delivered in two pieces upon the other side. That the iron be caught with requisite firmness the diameter of the blade must be at least eighty times the thickness of the sheet, so that, on account of the difficulty of constructing large steel discs, the application of this machine shear (which otherwise is mechanically complete) is limited to cutting thin sheets. Double-lever shears are shown in Figure 2. The two movable blades are screwed to a large trapeziform casting, which oscillates upon a bolt in the centre of the frame and receives on its upper end its motion by a circular eccentric working in a vertical slot. This eccentric is borne on a horizontal shaft, and by means of a pair of spur-wheels receives its motion from the fly-wheel shaft of a small steam-engine.
Figure 6 (pt. 3o) represents a punching-machine combined with a lever shear. A is the fixed blade of the shear, B the movable blade, C the punch, and D the die; a represents the rotating axis of the lever h, with which the movable blade of the shear as well as the punch is con nected. The rotating axis bears on its outer end a pulley (c), upon which acts a heart-wheel (d) that vibrates the lever b. The heart-wheel (d) receives a slow rotation from a driving-shaft by means of gear-wheels (c, /). Upon this shaft, besides the fly-wheel g, are the fast and loose pulleys upon which the belt runs. The objection to such lever shears is that with straight-cutting blades the angle under which the edges catch the material to be cut is variable and at first may readily be so large as to cause the material to be displaced by the blades. The punch C is shiftable in a prismatic guide (K) of the frame, and is moved downward by the short elongation of the lever b over a and upward by two draw ing-rods (1) so attached that they can be turned to both sides of the lever head.
Figure 3 (pl. 31) shows another combination of lever shear and punch ing-machine (De Bergue's). The movable shear-blade and the punch are, in a manner similar to that shown in Figure 2, secured to a trapeziform casting, which can be rotated about a horizontal axis and receives on its upper end a vibrating motion by means of a circular eccentric. This eccentric is keyed upon a hollow shaft enclosing the driving-shaft and receives a slow rotation by two pairs of gear-wheels. The fly-wheel shaft bears the driven pulley and gears through a pinion with the spur-gear shown in the front. This in turn drives the spur-gear which (shown at the back) vibrates the lever operating the shear and the punch.