few of the more familiar movements are here grouped and illustrated. If fully mastered and understood they will be of great assistance to the student of mechanics in understanding the more difficult and complicated descriptions and drawings of modern machinery.
Fig. 13 is a rack and pinion, for converting rotary motion into linear motion, or the re verse, according to whether the rack or pinion is the driver.
Fig. 14 shows a pinion between two racks. If the lower rack be fixed and the pinion rolled one foot the upper rack will move two feet. In this way the stroke of a piston can be doubled.
Fig. 15 is a gear-wheel and worm, for chang ing a rapid rotary motion into a very slow rotary motion. One rotation of the worm turns the gear-wheel the distance of one tooth.
Fig. 16 is a group of bevel gears, positioned as in the differential on the rear axle of an automobile. Either of the large bevel-gears may drive the other through the small bevel gear.
travels in the slot it raises• and lowers the rod r, rapidly in one direction, more slowly in the other.
Fig. 23 is a parallel motion. To whatever distance the bars are moved they are held parallel by the slanting connections.
Fig. 24 is a shears for cutting metal. The wheel no and pin operate the upper blade, giving a long leverage for increased shearing power.
Fig. 17 is a mangle wheel and pinion. The pinion P drives, traveling around the long C. shaped rack, rotating the mangle first into one direction then in the reverse direction.
Fig. 18 is a pair of eccentric gear-wheels, either of which may be the driver. The rota tion of the driven wheel is alternately slow and rapid.
Fig. 19 shows a couple of pump-cams. As they touch at every point of their rotation they Fig. 25 is a toggle- joint. Only a slight force is required to throw the two levers into line exerting a vastly multiplied energy over a short distance. It is used in to apply a sudden pressure.
Fig. 26 is a universal joint, permitting a rotating shaft to be bent to a slight angle as necessary, without interfering with its working. Fig. 27 is a three-throw cam. The pointed wheel measures the same at every point may be used to raise a column of water by lifting.
Fig. 20 is a diagram of a crank and piston movement. It will be noticed that the spot s on the centre of the piston rod describes an oval. The nearer this spot is placed to the piston the more elongated is the oval. If the student will make a pattern of this in card board and test it in various positions he will get a far better understanding of why a crank motion is so generally preferred in machinery of its diameter, and as it rotates giyes a rocaung motion to the rod, moving it, ck and forth three times to each revolution., Fig. 28 is a heart-cam for giving irregtdar reciprocation to the rod.
Fig. 29 is an ore-stamp. The m shaped like a long s raises the stamp twice'during each droi 7 revolution and leaves it free to dro by gravity.
Fig. 30 shows a drum-shaped cam C whose groove moves the shaft S of the large wheel W alternately to the right and left.
for altering rotary into reciprocating motion the change is so gradual that jar is obviated.
Fig. 21 is a lazy tongs or combination of levers which support each other and permit rapid change of position.
Fig. 22 is a combined bell-crank and wheel crank for altering rotary motion into recipro cating. The wheel drives and as the pin p Fig. 31 is an eccentric, or wheel mounted out of centre, so that through the encircling straps it gives a reciprocating motion to the rod. It is much used on steam-engines.
Fig. 32 is a pair of pulleys connected by a twisted belt for reversing the direction of rotation of one of the shafts.
Fig. 33 is a two-speed gear. The pulley a being the driver, the upper large pulley is driven on one speed; when the belt is shifted to b, which is a loose pulley there is no driving; when the belt is shifted to c the other drive at a different speed is effective.
Fig. 34 is the steering gear of a sailing is ves sel, showing how the turning of the hand-wheel w s made to shift the ropes rr and throw the tiller t of the rudder to right or left.
Fig. 35 is a positive "silent" chaili drive. Either the chain or gear-wheel may drive. It is used on auto-trucks and a variety of heavy machinery where belts are inadequate.