Channeling-machine Bits.—All percussive channeling machines carry a gang of cutters bolted together, and in every case the bits or points are chisel-shaped, some of them having straight edges and others diagonal ones. The cutting tools are in the shape of gangs, instead of being in solid bars, because they are more readily handled and transported to the blacksmith shop, and because the breakage of a bit is adjusted by replacing only one bar in the gang. A gang is used with the bar ehanneler, and sometimes with the track channelers in sandstone, or very soft material. The 5-drill gang is used with track channelers. The bits of the gang for channeling differ somewhat accord ing to the stone. For marble and limestone the points taper sharply, as shown in the figures. In sandstone the points are more blunt, with heavy edges, so as to prevent wear of gauge. it is also advisable in sonic kinds of sandstone to curve the cutting edge of the bit— that is, to make it convex, and thus prevent wearing of the gauge to a taper and " sticking." Sticking is a troublesome feature in sandstone quarries, because the bit wears away the gauge rapidly. The object of the diagonal bit is to maintain a level bottom to the channel. %Vithout it the channel would be " rutted." The edge of the diagonal bit cuts away what is known as the " frog." This frog is formed by glancing of the straight bit, it not being perfectly rigid, especially in deep cuts. The edge of the diagonal bit strikes the frog diag onally across the top. and thus cuts it away. In very deep channels it is sometimes advisable to use an extra clamp down in the cut, or above it, directly under the cross-head, in order to prevent springing of the bars.
Steel gang channeling machines, cut in marble from 75 to 125 sq. ft. of channel per day of 10 hours ; in oolitic limestone and in sandstone from 150 to 400 sq. ft. In marble channeling is done at from 10 to 25 cents per sq. ft., equivalent to from 3 to 5 cents per cub. ft. of stone quarried. ]n oolitic limestone and sandstone the cost is about one-half these figures.
The 111w-owl-Feather Proems is distinctly an American invention, the old system being a trench in the stone with a wedge for splitting. There arc many advantages in the plugs and feathers over wedges. Less stone is wasted, because the plug-and-feather process requires only a hole of small diameter while the wedge process involves a trench several inches wide at the top. The plug is a common piece of steel, wedge-shaped. The feathers are made of half-round iron, drawn down to a point which is bent over. When the hole has been drilled to the required depth, the feathers arc first inserted, then the plug is driven down between them ; thus a tension is exerted on the walls of the hole for the full depth of the feathers. It is obviously important in breaking up a block of stone that the break be true. With the
wedge process the force is exerted only at the top, hence the stone is apt to break irregularly, while with the plugs and feathers holes arc drilled sometimes to the full depth of the stone, and the plugs and feathers inserted for almost the full depth of the hole ; thins a straight and true break is made. The plug-and-feather process has followed the use of rock drills on quarry bars. Until recent years the wedge process was used in the Ohio sandstone quarries, and almost universally in Europe, but plugs and feathers have been adopted in progressive quarries.
Qoarrying by Wire Cord.—This method is exclusively employed at two marble quarries in Belgium. and is also in use for quarrying various descriptions of stone, including granite, in several countries of Europe. as well as it, Algeria and Tunis, not only subdividing blocks, but also sawing large masses out of the solid rock. For this purpose a cord, barely in. in diameter, composed of three mild steel wires, is made to travel at about 13 ft. per second, while the diameter is reduced and the speed slightly increased as the length of cut decreases fur subdivision of the blocks. The twist of the cord causes it, while running, to turn upon itself, thus becoming worn evenly over its whole surface, so that eventually it presents the appearance of a single wire, but little larger than those which originally composed the cord. It is then incapable of carrying along the sand and water, but may still be used for fencing and a variety of purposes. Before being worn cut, however, a cord 150 yds. long is capable of cutting to a depth of nearly 70 ft. in 15 blocks, or of producing about 500 sq. ft. of sawn surface in marble. In a block of marble 15 ft. long the rate of the cut is 14 in. per hour, and in granite about 1 in. One endless cord, guided by grooved pulleys, may be made to cut at several different places, provided they die not too close together ; and, as there is so little surface in contact, a very small amount of motive power is required todrive. The tension is maintained by a weighted truck on the incline, and the feed is given by an endless screw, rotated automatically in stone of uniform texture, or by hand when irregular ities are anticipated.
The Knox System of Blasting in Quarries.—The purpose of the Knox system is to re lease dimension stone from its place in the bed by so directing an explosive force that it is made to cleave the rock in a prescribed line, and without injury. The system is also used for breaking, up detached blocks of stone into smaller sizes. A round hole is first drilled— Fig. 14. A reamer, shown in end view in Fig. 14, and in elevation, Fig. 15, is inserted in the hole in the line of the proposed fracture, and made to cut two V-shaped grooves, A, B.