ROCK OIL 



711 



1720 



tion, so that it may be acted upon at the return stroke. At each change the steam is 

 admitted to the same end of the cylinder as the piston and the tappet struck, and, 

 there being a sufficient clearance 

 allowed, rushes in to cushion the pis- 

 ton and arrest and reverse the motion. 

 The self-acting feed-motion, where- 

 by the penetration of the rock, resulting 

 from the rapid succession of blows, 

 is mechanically accompanied by a cor- 

 responding advance in the boring 

 machine itself, is actuated by means of 

 another tappet, attached to the oppo- 

 site side of the cylinder, so as to pro- 

 ject into the cylinder at a point in the 

 lower clearance below the valve-tappet 

 and fitted with a spring for returning 

 it _into position after being struck ; 

 this feed-tappet is carried on to the 

 external spindle, extending the oppo- 

 site or upper end of the cylinder, and 

 there acting by means of a pawl upon 

 a ratchet-wheel or collar, attached to 

 the cylinder so as to -work round the 

 feed-screw ; and the action of this de- 

 vice is such that the feed is exactly 

 proportioned to the progress of the 

 work. If from excessive hardness or 

 any other cause, the blow is ineffective, 

 and the penetration deficient, i.e., less 

 than the distance between the valve 

 and feed-tappets, or ^ s ths of an inch, 

 the piston fails to actuate the feed- 

 motion, and the cylinder remains stationary for the time. It will readily be under- 

 stood that the cylinder is fitted so as to slide in the frame, which is a semi-cylindrical 

 shell, provided with V-shaped projections fitting into external grooves on the cylinder; 

 the feed-screw is attached by a collar to the curved arm or bar on the head of the 

 frame, and has a square head on which a winch-handle fits, whereby, when the cylinder 

 has been fed forwards by the ratchet-and-pawl motion to the end of the guides OP 

 slides, it may be brought back by hand, ready for further operations, for which a 

 longer drill-bar would have to be attached. 



There remains to bo noted another speciality in the mechanism, viz., the device 

 whereby the necessary continuous, step-by-step, and partial rotation of the drill-rod, 

 and piston is effected at each return stroke. This is effected by a peculiar rifling 

 arrangement, which is brought to bear upon the interior and upper part of the piston 

 and rod. For this purpose a suitably-rifled round steel-bar is attached by a collar to 

 the top cylinder cover, and provided with a ratchet and pawls, so that it is free to 

 rotate in one direction only ; this bar has eight spiral grooves, one complete turn in 

 7 feet being the pitch, and projects downward into a corresponding hole bored in tho 

 piston and rod, which are fitted with a brag- nut fitted thereto, and rifled to correspond. 

 By this means the rifled-bar and the piston and drill-bar are alternately made to 

 make Ath of a complete revolution at each stroke ; on the down-stroke of the piston, which 

 is straight, the rifled-bar is caused partially to rotate ; but as it cannot go back on the 

 upstroke, the piston takes the rifling and rotates partially in its turn ; and the stroke 

 and pitch are so proportioned that one entire revolution is made in about twelve com- 

 plete strokes. 



The smallest size of these rock-drills has a 2.^ -inch cylinder, and weighs only 173 

 Ibs. (cylinder 123 Ibs.); its piston-stroke is 3 } r inches, and it is capable of boring 

 holes from f-inch to if -inch diameter to 10 feet deep, averaging, in the hardest crystal- 

 lino trap-rock, about 35 feet linear of 1-inch bore-hole in a day of ten hours. In the 

 largest size, weighing 818 Ibs. (cylinder 558 Ibs.), 5-inches cylinder, tho stroke is vari- 

 able, 8 inches for soft, and 6-J- inches for hard rock. The drill-holes may be from 

 If to 5 inches, and to a depth of 40 ftet. With this machine a day's work of ten hours 

 would average 25 feet of 3f -inches bore-hole in the hardest trap. The small size 

 delivers 800, and the largo one 400 blows per minute. 



ROCKETS. See PYROTECHNY. 



ROCK FAT. See ADIPOCERE. 



ROCK OXXi. A name for petroleum. See NAPHTHA ; PAKAFFINE ; PETnoLEtf jr. 



