"If the mountain won't come to Mahomet," says the proverb, "Mahomet must go to the mountain."

This is as true in the workshop as outside;—Mahomet being the tool, the mountain the work on which it must be used. With the increase in size of machinery and engineering material, methods half a century old do not, in many cases, suffice; especially at a time when commercial competition has greatly reduced the margin of profits formerly expected by the manufacturer.

To take the case of a large shaft, which must have a slot cut along it on one side to accommodate the key-wedge, which holds an eccentric for moving the steam valves of a cylinder, or a screw-propeller, so that it cannot slip. The mass weighs, perhaps, twenty tons. One way of doing the job is to transport the shaft under a drill that will cut a hole at each end of the slot area, and then to turn it over to the planer for the intermediate metal to be scraped out. This is a very toilsome and expensive business, entailing the use of costly machinery which might be doing more useful work, and the sacrifice of much valuable time. Inventors have therefore produced portable tools which can perform work on big bodies just as efficiently as if it had been done by larger machinery, in a fraction of the time and at a greatly reduced cost. To quote an example, the cutting of a key-way of the kind just described by big machines would consume perhaps a whole day, whereas the light, portable, easily attached miller, now generally used, bites it out in ninety minutes.

PNEUMATIC TOOLS

The best known of these is the pneumatic hammer. It consists of a cylinder, inside which moves a solid piston having a stroke of from half an inch to six inches. Air is supplied through flexible tubing from a compressing pump worked by steam. The piston beats on a loose block of metal carried in the end of the tool, which does the actual striking. The piston suddenly decreases in diameter at about the centre of its length, leaving a shoulder on which air can work to effect the withdrawal stroke. By a very simple arrangement of air-ports the piston is made to act as its own valve. As the plane side of the piston has a greater area than that into which the piston-rod fits, the striking movement is much more violent than the return. Under a pressure of several hundreds of pounds to the square inch a pneumatic hammer delivers upwards of 7,000 blows per minute; the quick succession of comparatively gentle taps having the effect of a much smaller number of heavier blows. For the flat hammer head can be substituted a curved die for riveting, or a chipping chisel, or a caulking iron, to close the seams of boilers.

The riveter is peculiarly useful for ship and bridge-building work where it is impossible to apply an hydraulic tool. A skilled workman will close the rivet heads as fast as his assistant can place them in their holes; certainly in less than half the time needed for swing-hammer closing.

Even more effective proportionately is the pneumatic chipper. The writer has seen one cut a strip off the edge of a half-inch steel plate at the rate of several inches a minute. To the uninitiated beholder it would seem impossible that a tool weighing less than two stone could thus force its way through solid metal. The speed of the piston is so high that, though it scales but a few pounds, its momentum is great enough to advance the chisel a fraction of an inch, and the individual advances, following one another with inconceivable rapidity, soon total up into a big cut.

Automatic chisels are very popular with ornamental masons, as they lend themselves to the sculpturing of elaborate designs in stone and marble.

Their principle, modified to suit work of another character, is seen in percussive rock drills, such as the Ingersoll Sergeant. In this case the piston and tool are solid, and the air is let into the cylinder by means of slide valves operated by tappets which the piston strikes during its movements. Some types of the rock-drill are controllable as to the length of their stroke, so that it can be shortened while the "entry" of the hole is being made and gradually increased as the hole deepens. For perpendicular boring the drill is mounted on a heavily weighted tripod, the inertia of which effectively damps all recoil from the shock of striking; for horizontal work, and sometimes for vertical, the support is a pillar wedged between the walls of the tunnel, or shaft. An ingenious detail is the rifled bar which causes the drill to rotate slightly on its axis between every two strokes, so that it may not jam. The drills are light enough to be easily erected and dismantled, and compact, so that they can be used in restricted and out-of-the way places, while their simplicity entails little special training on the part of the workman. With pneumatic and other power-drills the cost of piercing holes for explosive charges is reduced to less than one-quarter of that of "jumping" with a crowbar and sledgehammers. With the hand method two men are required, usually more; one man to hold, guide, and turn the drill; and the other, or others, to strike the blows with hammers. The machine, striking a blow far more rapidly than can be done by hand, reduces the number of operators to one man, and perhaps his helper. So durable is the metal of these wonderful little mechanisms that the delivery of 360,000 blows daily for months, even though each is given with a force of perhaps half a ton, fails to wear them out; or at the most only necessitates the renewal of some minor and cheap part. The debt that civilisation owes to the substitution of mechanical for hand labour will be fully understood by anyone who is conversant with the history of tunnel-driving and mining.

Another application of pneumatics is seen in the device for cutting off the ends of stay bolts of locomotive boilers. It consists of a cylinder about fifteen inches in diameter, the piston of which operates a pair of large nippers capable of shearing half-inch bars. The whole apparatus weighs but three-quarters of a hundredweight, yet its power is such that it can trim bolts forty times as fast as a man working with hammer and cold-chisel, and more thoroughly.

Then there is the machine for breaking the short bolts which hold together the outer and inner shells of the water-jacket round a locomotive furnace. A threaded bar, along which travels a nut, has a hook on its end to catch the bolt. The nut is screwed up to make the proper adjustment, and a pneumatic cylinder pulls on the hook with a force of many tons, easily shearing through the bolt.

We must not forget the pneumatic borer for cutting holes in wood or metal, or enlarging holes already existing. The head of the borer contains three little cylinders, set at an angle of 120°, to rotate the drill, the valves opening automatically to admit air at very high pressures behind the pistons. Any carpenter can imagine the advantage of a drill which has merely to be forced against its work, the movement of a small lever by the thumb doing the rest!

Next on the list comes the pneumatic painter, which acts on much the same principle as the scent-spray. Mechanical painting first came to the fore in 1893, when the huge Chicago Exposition provided many acres of surfaces which had to be protected from the weather or hidden from sight. The following description of one of the machines used to replace hand-work is given in Cassier's Magazine: "The paint is atomized and sprayed on to the work by a stream of compressed air. From a small air-compressor the air is led, through flexible hose, to a paint-tank, which is provided with an air-tight cover and clamping screws. The paint is contained in a pot which can be readily removed and replaced by another when a different colour is required. This arrangement of interchangeable tins is also important as facilitating easy cleaning. The container is furnished with a semi-rotary stirrer, the spindle passing through a stuffing-box in the cover, and ending in a handle by which the whole thing complete may be carried about. The compressor is necessarily fixed or stationary, but the paint-tank, connected to it by the single air-hose, can be moved close to the work, while the length of hose from the tank to the nozzle gives the freedom of movement necessary. Air-pressure is admitted to the tank by a bottom valve, and forces the paint up an internal pipe and along a hose from the tank to the spraying nozzle, to which air-pressure is also led by a second hose. The nozzle is practically an injector of special form. The flow of paint at the nozzle is controlled by a small plug valve and spring lever, on which the operator keeps his thumb while working, and which, on release, closes automatically. When it is required to change from one colour to another, or to use a different material, such as varnish, the can, previously in use, is removed, and air, or, if necessary, paraffin oil, is blown through the length of hose which supplies the paint until it is completely clean." The writer then mentions as an instance of the machine's efficiency that it has covered a 30 feet by 8 feet boiler in less than an hour, and that at one large bridge yard a 70 feet by 6 feet girder with all its projecting parts was coated with boiled oil in two hours—a job which would have occupied a man with a brush a whole day to execute. Apart from saving time, the machine produces a surface quite free from brush marks, and easily reaches surfaces in intricate mouldings which are difficult to get at with a brush.

The pneumatic sand-jet is used for a variety of purposes: for cleaning off old paint, or the weathered surface of stonework; for polishing up castings and forgings after they have been brazed. At the cycle factory you will find the sand-jet hard at work on the joints of cycle frames, which must be cleared of all roughness before they are fit for the enameller. The writer, a few days before penning these lines, watched a jet removing London grime from the face of a large hotel. Down a side street stood a steam-engine busily compressing air, which was led by long pipes to the jet, situated on some lofty scaffolding. The rapidity with which the flying grains scoured off smoke deposits attracted the notice of a large crowd, which gazed with upturned heads at the whitened stones. A peculiarity about the jet is that it proves much more effective on hard material than on soft, as the latter, by offering an elastic surface, robs the sand of its cutting power.

After merely mentioning the pneumatic rammer for forcing sand into foundry moulds, we pass to the pneumatic sand-papering machine, which may be described briefly as a revolving disc carrying a circle of sand-paper on its face revolved between guards which keep it flat to its work. The disc flies round many hundreds of times per minute, rapidly wearing down the fibrous surface of the wood it touches. When the coarse paper has done its work a finely-grained cloth is substituted to produce the finish needful for painting.