ROCK DRILLS AND ROCK DRILL ING. The steam or rock drill is known to-day as an American invention and its inception dates back to the excavation of the Hoosac Tunnel in Massachusetts. This enterprise was fathered during its period of construction by the State of Massachusetts and was beset with enormous difficulties. To begin the exca vation of a tunnel five miles long through hard rock and to do the drilling by hand was an audacious proposition. Many methods of ex cavation were proposed and tried. Machines were built, tested and condemned. Among the inventors, the man who schemed the machine which in general features embodied the require ments of a perforator for making holes for blasting was Mr. Fowle of Boston. He con structed the first machine in which the drill used was made the extension of the piston rod of a reciprocating steam engine, which was moved forward toward the rock as the chilling advanced. The drill had a slow rotary as well as a reciprocating motion to ensure the boring of a round hole. With this beginning machines were improved in details, but operated without notable economy. The drills were heavy and could be used practically only when mounted on heavy carriages running on wheels on a track They were much too heavy for mine or (marry work, although a few were used for such purposes.
Later came a demand for a lighter machine, and the Little Giant and Eclipse machines, both built by the Ingersoll-Rand Company of New York, were found useful. The Little Giant was operated by a positive motion valve and the Eclipse by a piston valve. With the introduc tion of light drills came various improvements which were found to be invaluable as the scope for the use of the rock drill enlarged. In fact, almost a new drill was male when the machines were applied on a large scale in New York City for outside excavation at a tunnel under 42d street and under Hell Gate, and also in the hard ore mines of Lake Superior.
As soon as the rock drill attained a reason able state of perfection its improvement was immediately manifested to the world at large. It has often been called the advance agent of civilization, and it undoubtedly has a better claim to that title than any other mechanical invention of recent date. All modern engineer ing is dependent on its use, and problems which would be impracticable without this machine are rendered easy. Its influence on mining, quarry
ing, railroading and navigation has been felt all over the world. The roek drill has developed the mines and tunnels of the world. The work done by the rock drill may be said to be from 60 to 150 lineal feet of hole drilled per day of 10 hours in ordinary stone, including shifting and setting up of the drill, cleaning holes, etc. In tests and special cases the figures have been largely exceeded, sometimes as much as 400 lineal feet being made. Records of 24 inches per minute are not uncommon, all, of course, for down holes in favorable rock, but 71) feet per day of 10 hours in granite, including moving and setting up, averages a fair working basis. The cost of drilling in this way may be stated to vary from 21/2 to 13 cents per lineal foot, according to local conditions. From four to six cents per foot of hole drilled may be taken as the working figure for general calculations. and this includes all expenses. There are two distinct methods of machine drilling, one the auger drill, which bores the rock, and the other the percussion drill, such as the Little Giant or Eclipse, working by direct impact, that is, by striking repeatedly in the same spot and by simply bruising or chipping away the rock. Ex perience has proved that a reciprocating drill operates with the greatest economy and effi ciency. The following are improvements made in the rock as used to-day: Beginning with the cylinder of the drill, the method of using long bolts to hold the top and bottom heads in place with an elastic or spring buffer, whereby the blow (struck acci dentally upon either head by the piston) is absorbed, may be placed first. The method of gripp4A the steel and the chuck by means of the bolt and chuck key stands second.. The device of flanged and rotating bar dropped through the ratchet box marked a great ad vance in the art. The use of the taper throttle was also a very neat device for preventing leakage and providing a graduated admission of the working fluid. In passing from the cylinder to its mounting the most important achievement was in the very simple device of mounting the drill on the horizontal arm at tached to a vertical column, which in turn was mounted to a block and jacked in place by two screws, one on either end of the block. A kindred invention was the universal joint ap plied to the legs of a tripod.