Engineering and Contracting . Either a direct or an alternating currentmotor may be employed, the latter beingpreferred because it is a smaller, lighter,meclianically simpler, hardier machine, andmore nearly fool proof. Four differentspeeds may be obtained with the directcurrent and two from the alternating cur-rent motor—in the latter case full speedfor steady running and a considerablylower speed for starting a hole or work-ing through bad ground, with immediatetransition from the one speed to the other,as required. The controller is on the topof the motor and the operator at the drillcan st
Engineering and Contracting . Either a direct or an alternating currentmotor may be employed, the latter beingpreferred because it is a smaller, lighter,meclianically simpler, hardier machine, andmore nearly fool proof. Four differentspeeds may be obtained with the directcurrent and two from the alternating cur-rent motor—in the latter case full speedfor steady running and a considerablylower speed for starting a hole or work-ing through bad ground, with immediatetransition from the one speed to the other,as required. The controller is on the topof the motor and the operator at the drillcan start, speed or stop the motor bysimply pulling a cord, this being the onlyconnection. The electrical connection endsat the motor, both the hose and the cordinsulate the drill and the operator is neverexposed to the current. The 5-C electric-air drill may be re-garded as the full equivalent of the air drill of any make; of its com-parative efficiency something will be saidlater The power requirement for tliis. 2—Sketch of Drill Cylinder of Electric Air Drill. -initil a sufficiency has been provided. .-\tthe beginning of operation the influx ofair is rapid, so that no time is lost in get-ting sufficient pressure to begin with. Theadmission of air and also the apportion-ment of relative volumes thereof to the two•ends of the drill cylinder are easily ad-justed by the operator. The electric-air drill is not troubled bythe freezing up or choking of the ,because there is no Moreover,the air does not accumulate moisture, andthe temperature does not fall to the freez-ing point. Again, air becomes and remainsa constant vehicle for the conveyance anddistribution of the lubricant. A certainamount of oil being contributed to the sys-tem at regular intervals, it would be moredifficult to prevent than to insure its reach-ing every working part. The length of hose employed seems tobe limited to about 8 ft. on each side. TheIiose may be a
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Keywords: ., bookcentury1900, bookdecade1900, bookpublisherchicago, bookyear19
