Page:The American Cyclopædia (1879) Volume III.djvu/106

100 BORING FIG. 18. Air Compressor. ferred; and, in fact, in all modern blasting on a large scale, the greatest amount of dis- placement of rock is effected by blasts which are made in the holes drilled by machines. Among the most noted of the rock drills, having been the longest in use, and the principal one em- ployed in exca- vating the Hoosac tunnel, is the Burleigh drill, a general outline of which and its mode of working are represented under BLASTING. It is what is call- ed a percussion drill, that is, a drill whose bit is driven by blows against the rock, and is usually propelled, as are the other drills to be noticed, by compressed air, which is furnished by a double-cylinder pump, called the air compressor, fig. 18. The backward and forward motion of the piston rod to which the drill is at- tached is pro- duced in the same manner as in an ordi- nary high-pres- sure steam en- gine. The In- gersoll drill is especially . ef- fective in ex- cavating open cuts. In the engraving, fig. 19, c is the cylinder, s the steam or com- pressed air chest, Ji the pipe which sup- plies the com- pressed air, and p the screw for moving the drill forward, which may be done by the hand or by the rod gr, which is turned by an automatic ratchet movement. Various attachments are used for the purpose of rotating percussion drills as well as for feed- ing them, a general idea of which may be gathered from the following description of a Pie. 19. Ingersoll Drill. drill (fig. 20) invented by Prof. De Volson Wood of the Stevens institute at Hoboken, N. J. The piston, piston rod, drill holder, ratchet for rotation, and enlargement for regulating the feed, constitute a single piece of cast steel. The small valve a is operated by the recipro- cating movement of the plug J. Steam is ad- mitted behind the plug b so as to keep it con- stantly pressed against the plug c, which rests upon the conical surface d. During the back- ward movement of the piston the small valve is forced upward by the conical surface, and during the forward movement it is moved downward by the pressure of the steam behind FIG. 20. Wood's Drill. the plug l>. This small valve admits the motor so as to reciprocate the piston e, and this piston operates the main valve f. The length of the stroke is adjusted by simply turning the piece g. By this arrangement the valve is operated without shock, and hence will not break, and when properly set the main valve will not be opened until the blow is struck. The drill is seized and held automatically by the conical wedges i i, and is rotated by the sloping click k, which rotates about its back edge, coming in contact with sloping teeth I on the enlarge- ment of the piston rod. The click m prevents it from feeding forward, and the click n in a similar manner prevents it from feeding back. The thread on the screw o is made very steep, so that when the piston advances so far as to drive m out of bearing, the pressure of the mo- tor on the forward head, p, during the back- ward stroke of the piston, forces the cylinder forward, which will cause the screw o to turn, thus securing an advance feed. A false head, r, to prevent the piston from striking the rear head, has the motor admitted and retained be- hind it by a puppet valve. The diamond drill, owned by the American diamond drill company, the bit of which is the invention of Kodolphe Leschot of Paris, is a rotary machine, and of course differs widely in construction from those just described. There are several patterns and sizes ; that represented in fig. 21 is a small tun- nelling drill. It is so adjusted that it can be placed in any required position, moving as if on a universal joint. The bits, which are screwed on the end of the drill rod, are armed with black diamonds as represented in figs. 22 and 23. It will be observed that the diamonds are so arranged as to cut the hole larger than the diameter of the bit or the drill- Both the drill rod and the bit are hollow to admit w ater % which