710 



BOCK-DRILL 



solely upon, and proceeding pan passu with, the actual work clone, so that however 

 variable may be the hardness of the rock on which it is operating, the piston acts on 

 the feed-motion only when and so long as adequate penetration has been effected, 

 thereby conducing to rapid and regular drilling, and steady progress and work. It 



appears to be an economical and 



1718 effective machine, for all the 



operations of quarrying and 

 mining, for rock excavations and 

 removal by blasting, for shafts, 

 sewerage works, tunnels, drift- 

 ways, headings, &c., in mines, 

 quarries, and various other engi- 

 neering and constructive works. 

 It may be worked by steam or 

 compressed air, and so mounted 

 as to drift bore-holes horizon- 

 tally, vertically, or at any re- 

 quired angle. For example, as 

 shown in the engravings, the 

 ordinary tripod form (fig. 1718) 

 is suitable for ordinary vertical 

 drilling, and for boring holes in 

 very narrow and irregular places, 

 driftways, &c. ; for railway tun- 

 nels, and the heavier class of 

 operations, a car is employed with several drills mounted thereon (fig. 1719); and, 

 again, fig. 1720 shows the ordinary form of ' gadding car,' designed for boring hori- 

 zontal as well as vertical holes, to enable blocks of stone of any desired dimensions 

 to be taken out of a quarry. 



The mechanical construction and details are as follow : It is one of the class of 

 machines known as a percussive rock-drill, comprising a cylinder with a double-action 

 reciprocating and rotating piston, with a piston-rod terminating at its outer extremity 

 in a drilling or cutting tool. The drill-bar is raised by the upward pressure of the 

 expansive fluid employed, upon the piston, and falls on that being withdrawn, the im 

 pulse of the downward stroke being aided and intensified by the expansive pressure 

 when admitted, in alternation, to act upon the upper side of the piston ; this in case 

 of vertical downward drilling ; in horizontal and overhead drilling, the weight of the 

 piston, rod, and drill-bar is overcome, and the tool propelled against the rock to be 



1719 



bored, like a projectile from a gun, by the expansive force employed. The reciproca- 

 ting motion of the piston itself is the automatic agent in effecting the alternate open- 

 ing of the ports and the change of steam, induction, and eduction. Attached to the 

 cylinder is a steam-chest and common D slide-valve, actuated by two short valve- 

 stems, one at each end, which are worked by tappets having rounded shoulders, pro- 

 jecting into the cylinder, and so situated that the piston strikes against them at the 

 completion of its stroke in either direction ; on contact with either of the tappets, the 

 piston thus not only effects a suitable change of steam by means of the valves, but at 

 the, same time restores the other tappet, at the opposite end, to its due projecting posi- 



