Mohave County miner., 1912-09-21
The Karns Tunneling Machine.

The Committee on Science and the Arts of the Franklin Institute of Penn- sylvania, has awarded the Edward Longstreth Medal of Merit to John Prue Karns of Boulder, Colorado, for his Tunneling Machine, in considera- tion of facts (which indicate that the Karns machine will operate with econ- omy within the limits of commercial utility, and possibly with a very con- siderable degree of economy, depend ing on it's durability and the continuity with which it can be kept in opera, tion."
 As early as the fifties, efforts were made to perfect a satisfactory tunnel. ing machine, and in 1851 and 1858. patents were taken out in the United States and England for such machines. and many have been patented since, but these proved impracticable.
 The Karns Tunneling Machine is constructed to drive a six, foot hole in rock without the use of explosives The hole is made by steel cutters, in. serted in circular head, to which is imparted a reciprocatlng motion, from the cylinder of what is practically a very large air.drill, and rotary motion through rlhed nut. The later motion is intermittent, the nut being provided with dogs, and the head is rotated few degrees on each back stroke of the shaft which carries it, so that the cutters strike in a different place at each stroke. The shaft is sixteen inches in diameter and about twenty feet long, and substantially made. Reamers are provided for maintaining the gauge of the tunnel. All moving parts are carried on roller bearings.
 The committee watched the opera. tion of 8 machine at Johnstown, Penn. sylvana. driving a tunnel through horizontal strata of coal and hard, close grained rock. The tunnel had been driven 15O feet. The rate of driving was one and two feet per hour at eighty and l60 strokes per minute, respectively. It was driven from compressor of a capacity of 2,5OO cubic feet of air per minute, compressing to 100 pounds per square inch. The weight of the reciprocating parts of the machine was about seven and a quarter tons, and the stroke, seven inches. The tunrel surface was smooth and the gauge well maintain ed. The chips removed ranged from one-eighth inch to one inch. The temper of the cutters is varied for diff. ferent parts of the face, to maintain an even wearing surface. The chips were removed by flushing through an eight-lnch pipe.
 The inventor claims that the cost of drilling can be cut eighty per cent with his machine. The complete cost of installation is estimated to be about 3O,OoOS. Operating cost per twenty four hours is estimated at 1908, with coal at 3S per short ton, and labor at B per twelve-hour day. Interest and depl eciatiOn are figured at twenty per cent or POS per day, making the total per day for interest. depreciation and operation, 1908. At a rate Of drilling of eighteen inches per hour, the cost of excavation is about 5S per cubic yard. Taking the average figure for driving an eight-foot tunnel at lO$ per cubic yard, this means a saving of one- half in operating cost. The initial cost of the machine would be greater than Tn the ordinary method, but the compressor plant would be about the same.-Salt Lake Mining Review.