the same principle as that used in the Mont Cenis Tunnel, and a
description of one of them will give a good notion of the general
principle of all. We select a form devised by Mr. C. Burleigh, and much
used in America, where it has been very successfully employed in driving
the Hoosac Tunnel, effecting a saving in the cost of the drilling
amounting to one-third of the expense of that operation, and effecting
also a still greater saving of time, for the tunnel, which is 5 miles in
length, is to be completed in four years, instead of twelve, as the
machines make an advance of 150 ft. per month, whereas the rate by hand
labour was only 49 ft. per month. These machines are known as the
“Burleigh Rock Drills,” and have been patented in England for certain
improvements by Mr. T. Brown, who has kindly supplied us with the
following particulars:
[Illustration:
FIG. 180.—_Burleigh Rock Drill on Tripod._
]
The Burleigh perforator acts by repeated blows, like Bartlett and
Sommeiller’s, but its construction is more simple, and the machine is
lighter and not half the size, while its action is even superior in
rapidity and force. The Burleigh machines are composed of a single
cylinder, the compressed air or steam acting directly on the piston,
without the necessity of flywheel, gearing, or shafting. The regular
rotation of the drills is obtained by means of a remarkably simple
mechanical contrivance. This consists of two grooves, one rectilinear,
the other in the form of a spiral cut into the piston-rod. In each of
these channels, or grooves, is a pin, which works freely in their
interior: these pins are respectively fixed to a concentric ring on the
piston-rod. A ratchet wheel holds the ring, and the pin slides into the
curve, causing it to turn always in the same direction, without being
able to go back. By this eminently simple piece of mechanism, the
regular rotation of the drill-holder is secured. The slide-valve is put
into motion by the action of a projection, or ball-headed piston-rod, on
a double curved momentum-piece, or trigger, which is attached to the
slide-rod or spindle by a fork, thus opening and shutting the valve in
the ascent and descent of the piston. Fig. 180 represents one of the
machines attached in this instance by a clamp to the frame of a tripod.
The principal parts of the machine are the cylinder, with its piston,
and the cradle with guide-ways, in which the cylinder travels. The
action of the piston is similar to that of the ordinary steam hammer,
with this difference, that, in addition to the reciprocating, it has
also a rotary, motion. The drill-point is held in a slip-socket, or
clamp, at the end of the piston-rod, by means of bolts and nuts. The
drill-point rotates regularly at each stroke of the piston, making a
complete revolution in every eighteen strokes. For hard rocks it is
generally made with four cutting edges, in the form of a St. Andrew’s
cross, thus striking the rock in seventy-two places in one revolution,
each cutting edge chipping off a little of the stone at each stroke in
advance of the one preceding. The jumper makes, on an average, 300 blows
per minute, and such is the construction of the machine, that the blows
are of an elastic, and not of a rigid, nature, thus preventing the
drill-point from being soon blunted. It has been found in practice, that
a drill-point used in the Burleigh machine can bore on an average 20 ft.
of Aberdeen granite without re-sharpening. As the drill pierces the
rock, the machine is fed down the guide-ways of the cradle by means of
the feed-screw (see Fig. 180), according to the nature of the rock and
the progress made. When the cylinder has been fed down the entire length
of the feed-screw, and if a greater depth of hole is required, the
cylinder is run back, and a longer drill is inserted in the socket at
the end of the piston-rod. The universal clamp may be attached to any
form of tripod, carriage, or frame, according to the requirements of the
work to be done; it enables the machines to work vertically,
horizontally, or at any angle.
The following advantages are claimed for this machine: Any labourer can
work it; it combines strength, lightness, and compactness in a
remarkable degree, is easily handled, and is not liable to get out of
order. No part of the mechanism is exposed; it is all enclosed within
the cylinder, so there is no risk of its being broken. It is applicable
to every form of rockwork, such as tunnelling, mining, quarrying, open
cutting, shaft-sinking, or submarine drilling; and in hard rock, like
granite, gneiss, ironstone, or quartz, the machine will, according to
size, progress at the incredible rate of _four inches_ to _twelve inches
per minute_, and bore holes from ¾ in. up to 5 in. diameter. It will, on
an average, go through 120 ft. of rock per day, making forty holes, each
from 2 ft. to 3 ft. deep, and it can be used at any angle and in any
direction, and will drill and clear itself to any depth up to 20 ft.
The following extract from the “Times,” September 24th, 1873, gives an
account of some experiments with the machine, made at the meeting of the
British Association in that year, before the members of the Section of
Mechanical Science:
“Yesterday, considerable interest was taken in this section, as it had
been announced that a ‘Burleigh Rock Drilling Machine’ would be working
during the reading of a paper by Mr. John Plant. The machine was not,
however, in the room, but was placed in the grounds outside, where it
was closely examined by the members after the adjournment, and seen in
full operation, boring into an enormous block of granite. The aspect of
the machine cannot be called formidable in any respect, for it looks
like a big garden syringe, supported upon a splendid tripod; but when at
work, under about 80 lbs. pressure of compressed air, it would be deemed
a very revolutionary agent indeed, against whose future power the
advocates for manual labour in the open quarry, the tunnel, and even the
deep mine, may well look aghast. Placed upon a block of granite a yard
deep, the machine was handled and its parts moved by the fair hands of
many of the lady associates of scientific proclivities; but once the
source of power was turned on, the drill began its poundings, eating
holes 2 in. in diameter in the block of granite, and making a honeycomb
of it as easily as a schoolboy would demolish a sponge cake. It pounds
away at the rate of 300 strokes, and progresses forward about 12 in., in
the minute, making a complete revolution of the drill in eighteen
strokes, and keeping the hole free of the pounded rock. The machine was
fixed to work at any angle, almost as readily as a fireman can work his
hose; and its adaptation to a wide range of stone-getting, by drilling
for blasting, and cutting large blocks for building and engineering,
with a saving of capital and labour, was admitted by many members of the
section. The tool is called the ‘Burleigh Rock Drill,’ invented by Mr.
Charles Burleigh, a gentleman hailing from Massachusetts, United States.
The patent is the property of Messrs. T. Brown and Co., of London. The
principal feature of this new machine is, that it imitates in every way
the action of the quarryman in boring a hole in the rock.”
[Illustration:
FIG. 181.—_Burleigh Rock Drill on Movable Column._
]
Many forms of carriages and supports have, from time to time, been made
to suit the work for which the ‘Burleigh’ machines have been required.
The machine is attached to these carriages, or supports, by means of the
universal clamp, by which it can be worked in any direction and at any
angle. Of these carriages we select for notice only two forms, one of
which is shown in Fig. 181. This carriage can be used to great advantage
in adits and drifts. It consists of an upright column, with a screw
clamp-nut for holding and raising or lowering the machine, the whole
being mounted on a platform which can slide right across the carriage,
and thus the machine can be brought to work on any point of a heading.
It is secured in position by means of a jack-screw in the top of the
column; and as the carriage is mounted on wheels, it is easily moved to
permit of blasting. Fig. 182 represents a carriage which is the result
of many years’ experience with mining machinery, and it is considered a
very perfect appliance. It is constructed of wood and iron, and it runs
on wheels. The supports for the machines, four of which may be mounted
at once, are two horizontal bars, the lower of which can be raised or
lowered, as may be necessary. The two parallel sides of the carriage are
joined only at the upper side, and there is nothing to prevent it from
being run into the heading, though the way between the rails may be
heaped up with broken rock, if only the rails are clear. Drilling, and
the removal of the broken rock, may then proceed simultaneously; for, by
means of a narrow gauge inside the carriage rails, small cars may be
taken right up to the _débris_. It is made in different sizes, to suit
the dimensions of the tunnel required. To give the carriage steadiness
in working, it is raised from the wheels by jack-screws, and held in
position by screws in a similar manner to the carriage represented in
Fig. 181.
[Illustration:
FIG. 182.—_Burleigh Rock Drills mounted on a Carriage._
]
[Illustration:
FIG. 183.
]
An extremely interesting system of drilling rocks—totally different from
that on which the machines we have just described are constructed—has,
within the last few years, been introduced by Messrs. Beaumont and
Appleby. What does the reader think of boring holes in rocks with
diamonds? It has long been a matter of common knowledge that the diamond
is the hardest of all substances, and that it will scratch and wear down
any other substances, while it cannot itself be scratched or worn by
anything but diamond. In respect to wearing down or abrading hard
stones, the diamond, according to experiments recently made by Major
Beaumont, occupies a position over all other gems and minerals to a
degree far beyond that which has been generally attributed to it; for in
these experiments it was found that on applying a diamond, or rather a
piece of the “carbonate” about to be described, fixed in a suitable
holder, to a grindstone in rapid rotation, the grindstone was quickly
worn down; but on repeating a similar experiment with sapphires and with
corundum, it was these which were worn down by the grindstone. Without,
on the present occasion, entering into the natural history of the
diamond, we may say that there are, besides the pure colourless
transparent crystals so highly prized as gems, several varieties of
diamond, and that those which are tinged with pink, blue, or yellow, are
far from having the same value for the jeweller. Then there is another
impure variety called _boort_, which appears to be employed only to
furnish a powder by which the brilliants are ground and polished. In the
diamond gravels of Brazil, from which we derive our regular supply of
these gems, there was discovered in 1842 a curious variety of
dark-coloured diamond, in which the crystalline cleavage, or tendency to
split in certain directions (which belongs to the ordinary stones),
appears to be almost absent; and the substance might be regarded as a
transition form between the diamond and graphite but for its hardness.
This substance was until lately used for the same purposes as _boort_,
which is a nearer relative of the pure crystal, and like it, splits
along certain planes. It received from the miners the name of
“_carbonado_,” and with regard to the application we are considering, it
has turned out to be a sort of Cinderella among diamonds; for its
unostentatious appearance is more than compensated for by its surpassing
all its more brilliant sisters in the useful property to which reference
has been made. This Brazilian term is doubtless the origin of the
English name by which the substance in question is known among the
English diamond merchants, who call it “carbonate”—an unfortunate word,
for it is used in chemistry with an entirely different signification.
“Carbonate” it is, however, which supplies the requirements of the
rock-drill, and the selected stones are set in a crown, or short tube,
of steel, represented by _c_ in Fig. 183. In this they are secured as
follows: holes are drilled in the rim of the tube, and each hole is then
cut so that a piece of the diamond exactly fits it, and when this piece
has been inserted, the metal is drawn round by punches, so as almost to
cover the stone, leaving only a point projecting, _b b_. The portions of
the crown between the stones are somewhat hollowed out, as at _a_, for a
purpose which will presently be mentioned. The crown thus set with the
boring gems is attached to the end of a steel tube, by which it is made
to rotate with a speed of about 250 revolutions per minute while pressed
against the rock to be bored. Water is forced through the steel tube,
and passing out between the rock and the crown, especially under the
hollows, _c c_, makes its escape between the outside of the boring-tube
and the rock, thus washing away all the _débris_ and keeping the drill
cool. The pressure with which the crown is forced forward depends, of
course, on the nature of the rock to be cut, and varies from 400 lbs. to
800 lbs. In this way the hardest rocks are quickly penetrated—sometimes,
for example, at the rate of 4 in. per minute, compact limestone at 3
in., emery at 2 in., and quartz at the rate of 1 in. per minute. It is
found that, even after boring through hundreds of feet of such
materials, the diamonds are not in the least worn, but as fit for work
as before: they are damaged only when by accident one of the stones gets
knocked out of its setting; and this machine surpasses all in the
rapidity with which it eats its way through the firmest rocks. This, it
must be observed, is the special privilege of the diamond drill—that,
since the begemmed steel crown and the boring-rods are alike tubular,
the rock is worn away in an annular space only, and a solid cylinder of
stone is detached from the mass, which cylinder passes up with the
hollow rods, where, by means of certain sliding wedges, it is held fast,
and is drawn away with the rods.
When the diamond drill is used merely for driving the holes for
blasting, this cylinder of rock is not an important matter; but there is
an application of the drill where this cylinder is of the greatest
value, furnishing as it does a perfect, complete, and easily preserved
section of the whole series of strata through which the drill may pass
when a bore-hole is sunk in the operation of searching for minerals
(which is so significantly called in the United States “prospecting,” a
phrase which seems to be making its way in England in mining
connections); for the core is uniformly cylindrical, the surface is
quite smooth, and any fossils which may be present come up uninjured, so
far as they are contained in the solid core, and thus the strata are
readily recognized. Contrast this with the old method, where the
bore-hole in prospecting is made by the reciprocating action imparted to
a steel tool, and merely the _pounded_ material is obtained, usually in
very small fragments, by augers or sludge-pumps: the fossils, which
might afford the most valuable indications, crushed and perhaps
incapable of being recognized; and instead of the beautifully definite
and continuous cylinder, a mere mass of _débris_ is brought up. In the
prospecting-bores the diameter of the hole is from 2 in. to 7 in. The
size adopted depends on the nature of the strata to be penetrated, and
on the depth to which it is proposed to carry the boring. When the
strata are soft, the operation is commenced with a bore of 7 in., and
when this has been carried to an expedient depth, the danger of the
sides of the hole falling in is avoided by putting down tubes, and then
the diamond drill, fixed to tubes of a somewhat smaller diameter, will
be again inserted, and the boring recommenced; or the hole can be
widened, so as to receive the lining-tubes. Of course, in boring through
hard rocks, such as compact limestones, sandstone, &c., no lining-tubes
are necessary.
In a very interesting paper, read before the members of the Midland
Institute of Mining Engineers, by Mr. J. K. Gulland, the engineer of the
Diamond Rock-Boring Company, who have the exclusive right of working the
patents for this remarkable invention, that gentleman concludes by
remarking that “the leading feature of the diamond drill is that it
works without percussion, thus enabling the holing of rocks to be
effected by a far simpler class of machinery than any which has to
strike blows. Every mechanical engineer knows, often enough to his cost,
that he enters upon a new class of difficulties when he has to recognize
it as a normal state of things with any machinery he is designing that
portions of it are brought violently to rest. These difficulties
increase very much when the power, as in the case of deep bore-holes,
has to be conveyed for a considerable distance. Where steel is used a
percussive action is necessitated, as, if a scraping action is used, the
drill wears quicker than the rock. The extraordinary hardness of the
diamond places a new tool in our hands, as its hardness, compared with
ordinary rock, say granite, is practically beyond comparison. Putting
breakages on one side, a piece of “carbonate” would wear away thousands
of times its own bulk of granite. Irrespective of the private and
commercial success which this invention has attained, it is a boon to a
country such as ours, where minerals constitute in a great measure our
national wealth and greatness.”
The advantages of the diamond drill may be illustrated by the case of
what is termed the Sub-Wealden Exploration. From certain geological
considerations, which need not be entered upon here, several eminent
British and continental geologists have arrived at the conclusion that
it is probable that coal underlies the Wealden strata of Kent and
Sussex, and that it may be perhaps met with at a workable depth. If such
should really prove to be the case, the industrial advantages to the
south of England would be very great, for the existence of coal so
comparatively near to the metropolis would prove not only highly
lucrative to the owners of the coal, but confer a direct benefit upon
thousands by cheapening the cost of fuel. A number of property owners
and scientific men, having resolved that the matter should be tested by
a bore, raised funds for the purpose, and a 9 in. bore had been carried
down to a depth of 313 ft. in the ordinary manner, when a contract was
entered into with the Diamond Rock-Boring Company for a 3 in. bore
extracting a cylinder of rock 2 in. in diameter. The company, as a
precautionary measure, lined the old hole with a 5 in. steel tube; and
in spite of some delay caused by accidents, they increased the depth of
the hole to 1,000 ft. in the interval from 2nd February, 1874, to 18th
June, 1874–-the progress of the work being regarded with the greatest
interest by the scientific world. Unfortunately, the further progress of
the work has been prevented by an untoward event, namely, the breaking
of the boring-rod, or rather tube; and, although the company is prepared
with suitable tackle for extracting the tubes in case of accidents of
this kind, and generally succeeds in lifting them by a taper tap, which,
entering the hollow of the tube, lays hold of it by a few turns—yet, in
this instance, where there have been special difficulties, the
extraction of so great a length of tubes is, as the reader may imagine,
by no means an easy task. Six attempts have been made to remove the
boring-rods which have dropped down; but so difficult has this operation
proved, that, all these efforts having failed, it has been decided to
abandon the old work and commence a new boring on an adjacent spot. A
contract has been entered into with the Diamond Boring Company, who have
undertaken to complete the first 1,000 ft. for £600, which is only £200
more than it would have cost to completely line the old bore-holes with
iron tubes—an operation which was contemplated by the committee in
charge of the exploration. The terms agreed to by the company are very
favourable to the promoters of the Sub-Wealden Exploration, although the
cost of the second 1,000 ft. will be £3,000 more; and the committee are
relying upon the public for contributions to enable them to carry on
their enterprise. It is most probable that funds will be forthcoming,
and should the boring result in the finding of coal measures beneath the
Wealden strata, all the nation will be the richer and participate in the
advantages resulting from an undertaking carried on by private persons.
Already a totally unexpected source of wealth has been met with by the
old bore showing the existence of considerable beds of gypsum in these
strata, and the deposits of gypsum are about to be worked. Whether coal
be found or not found, there is no doubt that a bore-hole going down
2,000 ft. will greatly increase our geological knowledge, and may reveal
facts of which we have at present no conception.
[Illustration:
FIG. 184.—_The Diamond Drill Machinery for deep Bores._
]
The boring-tubes, it maybe remarked, are made in 6 ft. lengths, and are
so contrived that the joints are nearly flush—that is, there is no
projection at the junctions of the tubes. Fig. 184 is engraved from a
photograph of the machinery used for working the diamond drill when
boring a hole for “prospecting.” This looks at first sight a very
complicated machine, but in reality each part is quite simple in its
action, and is easily understood when its special purpose has been
pointed out. We cannot, however, do more than indicate briefly the
general nature of the mechanism. The reader will on reflection perceive
that, although the idea of causing a rod to rotate in a vertical hole
may be simple, yet in practically carrying it out a number of different
movements and actions have to be provided for in the machinery. The
weight of the rods cannot be thrown on the cutters, nor borne by the
moving parts of the machine—hence the movable disc-shaped weights
attached to the chains are to balance the weight of the boring-rods as
the length of the latter is increased. There must also be a certain
amount of _feed_ given to the cutters, regulated and adjusting itself to
avoid injurious excess: hence a nut which feeds the drill is encircled
by a friction-strap in which it merely slips round without advancing the
cutter when the proper pressure is exceeded. There must be means of
throwing this into or out of gear, or advancing the tool in the work and
of withdrawing it—hence the handles seen attached to the brake-straps.
Water must be drawn from some convenient source, and caused to pass down
the drill-tube—hence the force-pump seen in the lowest part of the
figure. The rods must be raised by steam power and lowered by mechanism
under perfect control—hence suitable gearing is provided for that
purpose.
The reader may be interested in learning what is the cost of
“prospecting” with this unique machinery. The company usually undertake
to bore the first 100 ft. for £40, but the next 100 ft. cost £80–-that
is, for 200 ft. £120 would be charged; the third 100 ft. would cost
£120–-that is to say, the first 300 ft. would cost £240, and so on—each
lower 100 ft. costing £40 more than the 100 ft. above it. Some of the
holes bored have been of very great depth, and have been executed in a
marvellously short space of time. Thus, in 54 days, a depth of 902 ft.
was reached at Girrick in a boring for ironstone; another for coal at
Beeston reached 1,008 ft.; and at Walluff in Sweden 304½ ft. were put
down in one week!