Weekly journal-miner., 1908-10-28
ECONOMY IN ROCK DRILLING
 HANGS ON DETAILS
lFrom Thursday's Daily)

Maximum economy in rock drilling and blasting depends rather on care ful observance of multiplicity of It. tie details, than upon the selection of any particular brand or style of roc% drill, says Mining Science.
 For all ordinary mining work. pa.- ticularly sinking and drifting in hard rock, No. 2, of 3la. machine, of any standard make, will give good satis- faction. Among the factors which make for fast drilling and rapid driv. ing are good strong machines. kept in first class repair; good air, that Is, air free from entrained moisture and uu. der pressure of so lbs. or 100 lbs, or even more; sharp. square.bittei steel of the smallest possible guage; usuing as few flat, dry holes as possi. ble; and arranging the work SO tho holes have good square starts. In all hard-rock mines, unless ventilation is extremely poor, it pays to drill small guaged holes, heavily burdened, and spring them n couple of times, so they will take big charge of explosive.
 Wherever number of machines are used, it pays 10 keep good man 70 look after the machine repairing and attend to extending the pipe lines, and 10 see they don't leak air. Tne machines should be taken apart, clean. ed, and broken or worn parts replaced at least every two weeks; the brass TO. tating nut in the piston, particularly, should be renewed at the slightest sign of wear. as in hard, slippy ground it is important that the drill Is twisted uniformly. IL also pays to frequently renew the chuck pushing, as with worn chuck pushing it is Impossible to chuck drill straight, and the starter wobbles all over the face in starting hole.
 The increasing tendency to use high. er air pressures for rock drilling is q very good one, and 1 have found it ad. vantageous to use pressures even up to l4O Tbs. At this latter pessure it is found that machines use very little more free air than at 100 lbs.
 In places where only 70 or 80 pounds or air is carried at the compressor, the pressure at the machines Is very weak, especially when two or three machines on one small pipe line are started up together In this case the machino drags the steel back and forth and wears the guage of the steel just as much as hard, solid blows.
 One of the most exasperating fea. tnres of drilling hard rock is the fire quent hturing" of the holes, caused by the steel glancing and deAecting when the hole encounters heads and slips at acute angles. When a nole htures before it is half way down, it is impossible to finish it, and a new hole should he started at once; however. most runners will twist and pound the chuck for an hour or so before they give hole up. The best way 10 guard against fturing is to have the steel guaged small, and instead of dropping the guage 3.l6 in. per foot. shade the guage Is in. or less. For \ ft. holes, use a 2.in. starter and fin. ish the hole lss in. or IF in, and use very long bits on the starters and sec. onds, the hits being made of cruel. form steel only triae smaller than the guage. These long bits tend to hole the hole pretty straight on the start. The long drills of the set should be of light steel and fitted with