No. 12
Should it happen, as it sometimes does, that after having gone through those operations, the quarrier fails in getting the cracked mass thrown down to the bottom of the quarry, he varies his mode of attack, and proceeds to bore a row of plug-holes on the face of the rock in such a line as to cut off a part from one end of the shaken mass; and for that purpose he is often obliged to hang a scaffold over the face of the rock on which to stand while boring the holes. Those plug-holes should be slightly inclined, so that, when the wedges, called plugs[21] and feathers, are driven into them, they may rend the rock in such a direction that the piece intended to be cut off may be a little narrower on the inner than the outer face, so that, thus resting on an incline it may be more easily taken out. The plug-holes should be cut at one foot asunder, and bored with a jumper 1¹⁄₂ inch diameter to the depth of 9 inches; and if the plug-holes be deep, and some difficulty in driving be expected, the plugs should be carefully greased or oiled previously to being driven. Having cut off a block as above described, an attempt may be made, if the mass be great, to throw it down by means of bulling; but if it be of lesser dimensions, and there be reason to expect that it may be removed in the ordinary way, the power of the crane may be applied to draw it down. For that purpose, the quarrier employs an instrument called a Dog, which is a strong short hook, armed like a pick on the point with steel, and having a ring in the end of it for the hook of the crane-chain to pass through. Having cut a small hole with a pick, on the upper part of the block which is meant to be removed, the steeled point of the dog is inserted into it, in such a manner that the weight of the crane-chain may retain it steadily in its place. Five or six men then heave on the crane a strain just as much as they suppose it may bear, without danger of carrying away any of its fixtures; and as many men as can find room are, at the same time, employed at the top of the rock, working with crow-bars behind the block, so as to shake it and loosen its hold. The two parties continue their work reciprocally, leading and following,—the men at the crane, still keeping up the strain, and taking care not to heave so much as to break any of the chains, while those on the top continue to shake the block by means of the crow-bars, or throw in stones into the opening, which is always getting wider between the block and the cliff, so as to prevent the loosened mass from falling back into its old place. When the block has been drawn as far forward as to appear just ready to fall over the cliff, one of the most expert men at the crane stands carefully watching the movement of the block; and whenever the stone begins to fall, he instantly throws the crane out of the gear, so as to prevent the wheelwork being pulled to pieces by the tumbling mass getting entangled in the chains, on which it frequently falls and breaks them to pieces. The operation of taking down large blocks from a great height is very tedious, and is often attended with much danger, as the stone, when it falls on the bottom of the quarries, makes the shivers among which it alights fly in all directions with a force which nothing can withstand.
[21] The plug ([fig. 12], c c′), and feathers ([fig. 12], d d′), are flat pieces of malleable iron, slightly tapered, and forming together a kind of compound wedge, the two feathers being first inserted into the hole, and the plug being driven between them by a series of gentle blows, from malls of the weight of from 30 lb. to 35 lb.
An opening being made in the manner above described, by getting one piece brought down, the same process is continued by cutting off and taking down pieces of eight or ten tons weight, until there be as many blocks in the floor of the quarry as can be easily managed at one time. Those masses are then arranged by means of the crane in convenient positions for being cut up into blocks of the requisite sizes; and as all of them are within range of the crane, they can with its assistance be easily turned over or set in any position. While some of the men are employed in cutting up those blocks, others are clearing away the rubbish, and others are boring holes or making ready for a fresh blast.
No. 13.
If those blocks, which we have supposed to be brought down to the quarry floor and to be ready for cutting, exceed seven feet in depth of cut, their farther subdivision will require the use of the plugs and feathers already described; but if their depth or thickness fall short of that, the ordinary iron wedges will answer. If the cut be of the depth of about 6 feet, the wedges must be placed about 3 inches apart from side to side; but if the depth of cut be less, they may be set 4 or 5 inches asunder. The method of setting in those wedges is as follows:—The person who cuts the wedge-holes generally works in a sitting posture, and if the block will admit of it, he prefers to bestride it, with a stone, as a stool, under each foot. He works with a pick of 16 lb. weight, having a handle only 16 inches long, with which he cuts the first hole generally about 3 inches from the end of the block. The holes are for the most part about 2¹⁄₂ inches deep, and 3¹⁄₂ inches long, and must be well cleared out at the bottom with a sharp pick; and the wedges must be set in a line as fair and straight as possible. Cutting wedges of that kind are of iron, from 7 to 9 inches long, and 2¹⁄₂ inches broad, and weigh about 7 lb. weight each. When in good order they must not be sharp in the mouth, but about ³⁄₈ of an inch thick, to prevent their grounding in the bottom of the hole; for if they but touch the bottom of the hole, they fly out at the first touch of the mall. When the wedges have been all properly arranged for a cut, the workman proceeds to give each of them in succession a gentle tap, so as to make them all fast; and for that purpose he uses a mall about 30 lb. weight ([fig. No. 13]), and having a handle 2 feet 9 inches long. He then goes over all the wedges, giving each of them a smart blow in regular, yet not too rapid succession, but allowing a little time for the parts of the stone to separate gradually. If the wedges be forced too quickly, there is great danger of the cut being spoiled by its flying out obliquely at one side, and thus not reaching throughout the whole depth of the block. The blocks, when thus subdivided by means of the wedges, are generally nearly of the size required by the rough moulds sent from the workyard, and are fit to be carried to the stone-cutter’s shed.
Fig. 14.
