The electric percussion drill in theory and practice

Wlherever rock is to be excavated, in mining, tunneling or quarryinig, there of necessity we find the percussion drill. Until about a year ago, two types of drills held the field, the lhand drill and the direct-acting steamn or air drill. With the extension of electrical metlhods of power transmission to mining operations, came the urgent demand for an electrically operated percussion drill. The mechanical and electrical requirements of this machine are particularly severe. It is called upon to continuously endure an action that is, in almost all other machinery, studiously avoided, namely, a practically uncushioned reciprocation and a blow upon substances harder than cast-iron. The general requirements of an electric percussion drill for mining work are that it shall be light enough to be quickly handled by two or three men; it must be powerful enough to compete with an air drill that absorbs eight or ten horse power; it must be so simple in its design that it can readily be repaired by an ordinary mechanic without electrical experience; it must be so constructed that the complete machine and its several parts can be soaked in mud and water without injury; it should be incapable of burning out; it must be able to endure almost any amount of the roughest handling without injury, and the mnaterials employed should be as little subject to crystallization as possible. In the electrical soliution of the problem, the solenoid and plunger affords the simplest method of developing this action, and most of the work in this field has been confined to this line. Although the introduction of the percussion drill has been attended with many diffictilties, I believe that the obstacles have been so far overcomne that the machine is today in thoroughly practical shape.