The possible resources of the various States of the Union are as follows: In the earlier days of the stone industry hand methods were employed almost exclusively in the work of quarrying and dressing. The past 25 years has, however, witnessed the in troduction of machinery and consequent changes. The old method of drilling and blast ing, formerly applied to all classes of rocks, is now done away with, excepting in the very hardest and toughest of materials, or where, in the case of granite and trappean rocks, the material is to be utilized only for roads. Even where drilling and blasting are now resorted to, it is the custom to drill a series of holes on the line along which it is desired the stone shall break; these holes are then charged somewhat lightly with a slow-burning black powder and fired simultaneously. In this way the force of the explosion is delivered along a consider able surface and the danger of shattering the material through the sudden jar is reduced to a minimum. This process is at present largely limited to granite rocks which are too hard to be quarried by means of channeling machines.
Plug and Feather Work.— In quarries where good breaks require that the splitting strain be exerted well down in the ledge, ex perience has shown that the best method for getting out the material is usually the plug and feather system, in which a series of holes from one and one-quarter to two inches in diameter and of a depth from two-thirds to the full thickness of the sheet are drilled at intervals depending upon the character of the stone and its manner of cleavage. Two feathers flat pieces of steel rounded on one side to fit the curve of the drill hole — are placed at the sides of the hole and the long-tapered wedge-shaped plug driven down between them. The material splits away in fairly regular blocks which must be otherwise cut to size by hand. The plug and feather method is still extensively in use for splitting large blocks of granite and marble. Holes three inches deep and five-eighths inch in diameter will serve for splitting blocks three feet deep and five-inch holes three-quarter inch in diameter for six-foot blocks. For marble and sandstone the holes have to be slightly deeper. In soft material such as sandstone, a drill mounted on the usual tripod finds frequent use, and this is far superior to hand methods, still in certain classes of work a drill mounted on a quarry bar will do much more and better work.
The advantages of the quarry bar are that all the holes are drilled to double length, intermediate ones being shallow. The lower half of the deep holes is drilled with a smaller drill bit so as to alternate the plug strain top and bottom and control the break by skillful sledging. In some instances compressed air at a pressure of 70 to 100 pounds is piped into the drill holes to ex tend a crack already started.
The wedges of the short hole tend to split along the, top and those of the long hole split along the bottom, thus distributing the pressure and tending to split the stone in a clean, smooth plane and largely avoiding any tendency to run off. This distribution of splitting strains is to
be worked out by experience in the peculiarities of the different ledges. The wedges or plugs need not in all cases be of a length equal to the depth of the holes. In some marble quarries, plug holes only five-eighths inch in diameter are put clear through the blocks, sometimes 10 feet deep, to weaken the line and ensure a straight break, the plugs, however, being shorter. This operation is much simplified by the use of the hammer-drill actuated by steam or compressed air.
Broaching.— In granite and other hard stones holes must be placed closer together and, as a rule, splitting across the grain is abandoned in favor of broaching. In this system, a series of holes is drilled, usually about three inches apart from centre to centre, leaving walls of three-quarters inch to two inches between, de pending upon the hardness of the rock, and a flat bit or Is subotituted for the regular steel. This has a face about three inches by three-quarters inch thick and is forged with a blunt end to crush this wall or web between the holes. Drills used for broaching must have the release which is a simple device to throw the pawls out of action and allow the drill to work without rotating. Broach channeling is the best and cheapest method of cutting out key blocks, lumps, and making wall cuts, etc., in granite quarries, where the rock is too hard to be cut advantageously with the regular channel ing machine.
Channeling Machines.— Channeling ma chines are utilized in the case of rocks of the nature of marble; limestone and the softer sand stone, since they would be liable to injury through blasting and since it is desired to re move the materials from the quarry bed with a minimum amount of waste and in such size and shape that they may be cut into suitable dimen sions. The Wardwell channeling machine, the earliest in use, has given way to the direct-act ing stone channeling machine, the design of which was based upon the conviction that the same principles which had made the Ingersoll Sergeant drill famous would, properly applied, give the best results in cutting a channel. It was believed that the direct-acting machine pos sessed points of decided advantage over the slow, cumbersome diamond and lever types of rock-cutting machinery of that day. Although certain shortcomings appeared in the first mod els, still it is an interesting fact that some of these first machines are in service to-day after more than 15 years of continuous use and are still doing good work. The success of these pioneer types demonstrated beyond ques tion the merit of the direct-acting principle now everywhere conceded as the correct one and it remained only to develop to the utmost the details of mechanical construction.