. Machinery for metalliferous mines : a practical treatise for mining engineers, metallurgists and managers of mines. g either the front or back end of the cylinder, two strong THE COMPOUND ROCK DRILL. l6 = Steel springs are used as buffers. These springs are placed on theback head, and are connected with the front head through side bolts,in such a manner that a blow either on the front or back heads iscushioned by the springs and a breakage prevented. The feeding of the IngersoU-Sergeant drills, and, indeed, of all drillsused in mining or tunnelling, is now effected by hand ; but for surfacew
. Machinery for metalliferous mines : a practical treatise for mining engineers, metallurgists and managers of mines. g either the front or back end of the cylinder, two strong THE COMPOUND ROCK DRILL. l6 = Steel springs are used as buffers. These springs are placed on theback head, and are connected with the front head through side bolts,in such a manner that a blow either on the front or back heads iscushioned by the springs and a breakage prevented. The feeding of the IngersoU-Sergeant drills, and, indeed, of all drillsused in mining or tunnelling, is now effected by hand ; but for surfacework with large drills making vertical holes an automatic feed attachmentis of great value, especially in countries where skilled men for runningthe drills are scarce, and one man has to look after several drills, however, are not within the scope of mining proper, andso do not demand a detailed description. The Optimus Compound Rock Drill.—There are many reasonswhich prevent the ordinary rock drill from being worked with the sameeconomy of steam or air as is effected in a high-glass engine. As a. Fig. 114.—The Optimus Compound Rock Drill rule, the waste of air is very considerable, varying, of course, accordingto the numerous devices of different makers for controlling its admissionto, and exhaust from, the cylinder. In the Optimus drill, manufacturedby Messrs. Schram and Co., the compound principle has been broughtinto play, and is said to effect a saving of 45 per cent, of air less thanthat of any other drill of the same size. A general view of the machine will be seen in fig. 114, and a sectionin fig. 115. The lower end of the cylinder is bored out to a largerdiameter than the upper, and the air under pressure used for the forwardstroke instead of being exhausted into the atmosphere in the usualmanner is conducted to the front end of the cylinder, and, acting uponthe increased area of the piston, is utilised for the backward stroke,thus effecting the above
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