The copper era., 1908-11-12
Economy in Rock Drilling Discussed By
 An ExDeFt,
Time rable No. s2.

1ul observance or multlplClty or little details, than upon the selection of any particular brand or style of rock drill.
 For all ordinary mining work, par ticularly sinking and drifting in hard rock, a No. 3, of B machine, of any standard make, will give good satis- faction. Among the factors which make for fast drilling aLd rapid driv- ing are good strong machines, kept in first-class repair; good air, that is, air free from entrained moisture and under pressure Of 80 or 100 pounds or even more; sharp, square-bitted steel of the smallest possible guage: using as few flat, dry holes as possi- ble; and arranging the work so the holes have good square starts. In all hard rock mines, unless ventilation is extremely poor, it pays to drill small guage holes, heavily burdened. and spring them a couple of times, so they will take a big charge of ex- plosiEe.
 Wherever a number Of machines are used, it pays to keep a good man to look after the machine repairing and attend to extending the pipe lines, and to see they don't leak air. The machines should be taken apart, cleaned, and broken or worn parts re- placed at least every two weeks: the brass rotating nut in the piston, par ticularly, should be renewed at the slightest sign of wear, as in hard, slippy ground it is important that the drill is twisted uniformly. It also pays to frequently renew the chuck pushing, as with a worn chuck bush ing it is impossible to chuck drill straight, and the starter wobbles all oyer the face in starting a hole
 The increasing tendency to use higher air pressures for rock drilling is a very good one, and [ have found it advantageous to use pressure even up to 14O pounds. At this latter pressure it is found that machines use very little more free air than at 10) pounds.
 In places where only 70 or 80 pounds of air is carried at the compressor, the pressure at the machines is very weak, especially when two or three smachines on one small pipe line are started up together. In this case the machine drags the steel back and forth and wears the guage of the steel just as m uch as hard, solid blows.
 One of the most exasperated feat ures of drilling hard rock is the ire quent "fturing'' of the holes, caused by the steel glancinp and dehecting when the hole encounterers heads and slips at acute angles. When , hole futures before it is half way down, it is impossible to finish it, and new hole should be 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 to guard against tturing is to have the steel guaged small, and in- stead of dropping the guage 3-16 | inches per foot, shade the guage Is inch or less. For eight feet holes, | use a 2-inch starter and finish the | hole 2 inch or T. inch, and use very long bits on the starters and seconds, | the bits being made of cruciform | steel only a trife smaller than the | guage. These long bits tend to hold ! the hole pretty straight on the start. The long drills of the set should be 1 of light steel and fitted with shorter | bits, so the drill can weave around d | little to follow the hole if it runs little crooked. The bits should be. square and the corners sharp. When | starters with big wings and with the corners dubbed back are used to be- 1 gin hole. the hole will rifle more or less if the rotating mechanism of ! the machine is the least worn: then, | as the hole goes down, the steel will | be twisted with difficulty and easily | sheared off by slip.
 Another advantage of using small | starters and using very little drop to the guage is, that the hole drills 1 much faster; a Finch starter will l drill one foot in five minutes, where ! a g inch starter would require about . seven minutes; from this it follows that large bits wear their guage faster than small bits.
 It is always good policy, when driy- ing drifts and crosscuts in hard ground, to drill the full round before blasting. h some localities the ma chine men drill and blast the incut first, and then hig up and drill squar- ing holes, as a slanting face is left when the cut holes kick out, and it takes as long to get hole started, in hard rock, on slanting face as it does to drill the entire hole after the start is made. For the same reason, l prefer a ''V'' in-cut to d ''draw" or "side-cut," unless there is an ex- ceptioually good floor or slip to break to. With side or bottom in-cut,