Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/462

Rh 444 MINING [BREAKING GROUND. FIG. 15. Diamond Drill. Diamond process of making bore-holes is the introduction of the drill. diamond drill. The working part of the drill consists of the so-called crown, which is a short piece of tube made of cast steel, at one end of which a number of black diamonds are fastened into small cavities (fig. 15). The crown is screwed on to wrought- iron pipes, which constitute the boring rod. Machinery at the surface causes the rod to rotate, and the result is the cutting of an annular groove at the bottom of the hole, leaving a core, which, breaking off from time to time, is caught by a little shoulder, and brought up to the surface with the rod. In places where it is not necessary to make any verification of the rocks tra versed, the crown is arranged with diamonds in the centre also. The debris, in either case, are washed away by a stream of water, which is forced down the tube and flows up the sides of the hole. With this system a bore-hole can be deepened continuously at a speed altogether unattainable by the other methods, which require stoppages for cleaning out. It has the further advantage of making it possible to drill holes in any direction ; and prospecting diamond drills are constantly used with much success inside many metal mines, especially in the United States. Fig. 16 1 shows the Little Champion Rock-Drill,which is largely em ployed in the Lake Superior district for prospecting. It can be used above or below ground. Two inclined cylinders drive a horizontal crank shaft, which works bevel gear, causing the drill to revolve. At the same time a countershaft is likewise set in motion, and this effects the advance of the drill by gearing driving the feed-screw ; as there are three kinds of gearing, the speed can be varied at pleasure. The feed-screw and its connexions are carried by a swivel-head, and this can be turned so as to drill holes at an angle. The drum shown above the cylinders is used for hoisting out the drill-rods by a rope. The rods are lap-welded iron tubes If inches in diameter, fitted with a bayonet joint. Another light portable prospecting drill for underground work is FIG. 16. Little Champion Rock-Drill. Fig. 17. represented in fig. 17. 2 It is intended for drilling holes 1 inches in diameter to a depth of 150 feet. The cores which it yields are inch in diameter. It has double oscillating cylinders 3 J inches in diameter with 3^ inches stroke, which are run up to a speed of 800 revolutions. The drill can be set to bore in any direction by turning the swivel-head on which it is carried. The larger rock-drill used by the American Diamond Rock Boring Company for putting down holes to a depth of 2000 feet consists of a 20 horse-power boiler with two oscillating 6-inch cylinders and the necessary gearing for working the drill, all 1 Engineering and Mining Jour., vol. xxxiii. p. 119. 2 Ibid., vol. xxxiii. p. 273. F IG ig. -Poll-pick. FIG. 19. Double- pointed Pick. mounted upon a carriage, so that the whole machine is readily moved from place to place. The feed is effected by gearing or by hydraulic pressure ;_a 2|-inch crown is employed, leaving a 2-inch core. Each separate drill-rod is 10 feet long. The total weight of the machine is about 4 tons. 4. Breaking Ground Tools Employed Blasting l&amp;gt;y Various Methods Machine Drills -Driving Levels and Sinking Shafts. The kind of ground in which mining ex cavations have to be carried on varies within the widest limits, from loose quicksands to rocks which are so hard that the best steel tools will scarcely touch them. Loose ground can be removed with the shovel ; but in Tools. the special case of peat sharp spades are employed, which cut through the fibres and furnish lumps or sods of con venient form for drying and subsequent use as fuel. What is called fair, soft, or easy ground, such as clay, shale, decomposed clay -slate, Q and chalk, requires the use of the pick and the shovel. The pick is a tool of very variable form, accord ing to the material operated on. Thus there are the navvy s pick, the single-point ed pick with a striking head at the other end called the poll- pick (fig. 18), and numerous varieties of the double-pointed pick (fig. 19), the special tool of the collier, but also largely used in metal mining. When the ground, though harder, is neverthe less &quot;jointy,&quot; or traversed by many natural fissures, the wedge comes into play. The Cornish tool known as a gad is a pointed wedge (fig. 20). The so-called &quot; pick and gad &quot; work consists in breaking away the easy ground with the point of the pick, wedging off pieces with the gad driven in by a sledge or the poll of the pick, or prizing them Q off with the pick after they have been loosened by the gad. The Saxon gad is held on a little handle, and is struck with a hammer. It is used for wedg ing off pieces of jointy ground, and in former days even hard rocks were excavated by its aid. The process consisted in chipping out a series of parallel ^^- ^ grooves and then chipping away the ridges left between the grooves. As a method of working this process is obsolete; but it is useful on a small scale for cutting recesses (hitches) for timber, for dressing the sides of levels or shafts before putting in dams, and for doing work in places where blasting might injure pumps or other machinery. We now come to hard ground ; and in this class we have a large proportion of the rocks met with by the miner, such as slate of various kinds, hard grits and sandstone, limestone, the metamorphic schists, granite, and the contents of many mineral veins. Rocks of this kind are attacked by boring and blasting. The tools employed are the jumper, the borer or drill, the hammer, the sledge (mallet, Cornwall), the scraper and charger, the tamping bar or stemmer, in some places the pricker or needle, the claying bar, the crowbar, and finally the shovel for clearing away the broken rock. The jumper (fig. 21) is merely a long bar of iron terminating in two chisel-like edges made of steel; Fig. 21. generally there is a swelling in the middle, and sometimes the jumper tapers all the way from the middle to the edge or bit. The juniper is most commonly used when it is necessary to bore holes downwards, and is