456 BORING 



of cylinder 4 inches, piston-rod 2i inches, diameter of back rod 1-^ths inch, area for 

 blow 10 square inches, for return 7 T 5 ths square inches, pressure for blow at 60 Ibs. per 

 square inch 500 Ibs., and for return of piston 380 Ibs. Stroke of slide-valve 5 to 3 

 inch, opening of steam port ^ -thto J inch, length of steam port 6 inches, area of steam 

 port l inch, diameter of steam-pipe 1| inch, stroke of piston-rod 2 to 4 inches. 

 Turning motion one revolution to sixteen blows. The consumption of steam and air 

 for a 4-inch stroke including portway clearances is about 90 cubic inches, or 19 strokes 

 per cubicfoot. Sec Specifications of Patents, No. 1,104, April 14, 1870, and No. 3,131, 

 Nov. 20, 1870. 



The Burlcigh Drill in its general arrangements does not differ essentially from 

 some of those which have been described. It has been used in several mines and 

 quarries in this country, and rather extensively in America. See Specification and 

 Illustration of Drill, No. 3,065, A.D. 1866. 



The main elements of this drill are the cage, the cylinder, and the piston. The 

 cage is merely a trough, with ways on either side in which the cylinder, by means of 

 a feed-screw and an automatic feed-lever, is moved forward as the drill cuts away 

 the rock. 



The piston moves backwards and forwards in the cylinder, and is propelled and 

 operated on substantially like the piston of an ordinary steam-engine. The drill 

 point is attached to the end of the piston-rod, which is a solid bar of steel. 



The forward motion of the cylinder in the trough is regulated by an automatic feed, 

 as the rock is cut away. 



It is driven by steam or compressed air as a motive power, and with a pressure of 

 50 Ibs. to the inch, strikes from 200 to 300 blows per minute, according to the size 

 of the machine. 



The valve used to control the entrance into and egress from the cylinder of tho 

 impelling medium is the ordinary D or locomotive slide-valve, which is operated by a 

 valve-rod attached to a pivoted piece made sufficiently heavy to possess considerable 

 momentum when put in motion. 



Tho body of the machine is made in one casting, and constitutes the steam or air 

 cylinder and covers and protects most of the feeding and turning mechanism. This 

 body has two wings forming part of a support or carriage, so that the drilling machine 

 may be presented to its work in any direction and at any angle. 



The cylinder a has its front end closed by a head c, into which a long stuffing box 

 d is screwed. 



To prevent any injurious variation between the amount of the feed and the pene- 

 tration of the drill, mechanism is introduced which automatically preserves a practical 

 uniformity of feed and penetration. When the feed of the cylinder is in excess of 

 the penetration of the drill, in which case the tappet r does not in the forward stroke 

 of the piston reach and displace tho paul and consequently no feed takes place until 

 the penetration of the drill equals the previous feed or advance of tho cylinder. As 

 it may occur when a feed of the cylinder takes place, that the piston on its back 

 stroke might possibly come in contact with tho back cylinder head g, a rubber 

 cushion d is placed against the rear-head u, to act as an elastic cushion to check the 

 back stroke of the piston by impact of tho tappet on tho piston-rod with the pro- 

 tecting plate facing the cushion. 



There are several forms of carriages for mounting drills for tunnel work. That 

 used for the Burleigh drills consists of a trolly on four wheels, with a moveable support, 

 which is actuated horizontally across the trolly and tho face of the drift by means of 

 a screw. The hollow bar or stretcher -which fixes the carriage when it is in position 

 for work, is held by a moveable support, and fixes itself by means of a screw at the 

 bottom. To this hollow shaft or upright stretcher the drill is attached by a clamp ; 

 the drill is raised or lowered by moans of a lever, having for its fulcrum a pin in 

 either of tho holes in the two bars of iron attached to the moveable support at their 

 bottom ends, and to the hollow shaft at the top ends. When the drill is fixed in 

 position, these bars are allowed to fall back by the removal of the pin at the top 

 which connects them to the hollow shaft. 



It is designed to be worked by one man, and may run on rails laitf for the pur- 

 pose. 



The compressed air for those machines has been carried through 7'160 feet of an 

 8-inch iron pipe ; and tho average difference in pressure at the compressors, and tho 

 heading of the tunnel, with an average of six drills in operation, was but 2 Ibs. to the 

 inch. 



Inger&oVs Drill. This drill, the invention of an American, is entirely automatic in 

 its movements, that is, the borer is turned by a twist bar arrangement, as in Jordan 

 and Darlington's Borer, patented in 1866, while the advance of tho tool and movement 



