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.
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.