Chapter 4: Portable Tools

“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.