Coal-Drill (Fig. 1) is a simple form of hand-tool. When in position, the post is fastened securely to the roof and the floor of the mine. The nut through which the screw-rod turns is placed in any of the slots cut in the post in order to get the proper pitch of hole to be drilled. The steel bits slip into the socket at the end of the screw-rod, and are made in different lengths to snit the depth of hole to be drilled—for instance, if a 6-ft. hole is to be drilled. a steel bit 2 ft.
long is first used, then it is replaced by a steel bit 4 ft. long, and finally by one 6 ft. lot_.
The screw-rods or feed-bars are made with 6. i. 10, 12, and 14 threads per inch, a range which fits the drill for all grades of hard coal or rock.
Watts' Drill for Boring and Reaming (Fig. 2) is specially adapted for boring into coal-banks.
The machine is provided with an expansible bit, which remains in its closed or normal position while the hole is being bored. When a previously determined depth is reached. the bit is expanded to create pocket at the end of the bore for the reception of a large amount of powder.
The figure shows an enlarged vertical section through the outer end of the auger-casing. The drive-shaft is provided with a longitudinal face groove extending practically from end to end, and at its forward or inner extremity it socket is fast ened to the shaft, At. the rear of the guide-box a spur-wheel is connected with the drive-shaft by a feather passing through the hub and entering the groove of the shaft. By this means when the wheel is revolved to turn the shaft, the latter is free to move forward. When a hole has been drilled the desired depth, a thumb-screw is turned, which holds the clamp tightly to the frame and stops the forward movement of the casing without preventing the casing from turning. By further manipulation the be comes stationary and forces the bit rod outward, thereby causing the bit-members to expand. When the pocket has been properly formed, the bit-rod is drawn backward, the bit assumes its normal position, and may be readily removed from the hole.
The Jeffrey Posilire-Peed Coal Drill consists of a small rotary en gine hung in an upright frame, hav ing joints at top and bottom to en gage by adjusting screws with the roof and floor of the mine. This is supported by a dog Or brace. to stiff en and hold the frame rigid as the anger bit advances into the coal. Power is transmitted to this auger bil or feed-bar through two gear wheels. Attached to the engine are feed-nuts that open nod close upon the feed-serew, which is -I to 5 ft. in length, on one end of which is a square socket. into which is inserted
the square end of the anger-hit. Two bits are used for convenience, one :1 ft. and the other 6 ft. long, biring a hole It to 2 in. in diameter, as may be required. Seven, eight, and nine foot auger bits are used to good advantage.
The Jeffrey Air-Feed Drill (Fig. 3) is similar in many respects to the positive-feed drill. In place of the feed-screw it has a feed-tube containing a piston, in the end of which is at tached a suitable smooth feed-bar. 3 or 4 ft. in length. having a square socket, into which the auger is fastened. This tube arrangement is adjustable in all directions, so that the drill will accommodate itself to any mine. Only one hose connection is required to operate the drill, the feed to the tube and engine being controlled by means of a three-way valve. In oper ating, the engine is started first, after which the air is turned into the tube, which forces the piston forward until it travels the full length of the air-tube. The air is then shut off from the feed and allowed to escape, and the feed-bar is pushed back into the tube. The advantage this drill has over the serew-feed is that the air acts as a cnthion when striking an unseen sulphur ball or rock, which al lows the auger to advance more slowly, preventing strain upon the machine. The apparatus drills a hole 1 to 2 in. in diameter to a depth of 6 ft. in four minutes, and can be set and started in less than two minutes.
The Jeffrey Coal-Xining Ma chine (Fig. 4) consists of a bed-frame occupying a space 2 ft. wide by 7 ft. 6 in. long, composed of two steel chan nel bars firmly braced, the top plates on each forming racks with their teeth downward. into which the feed-wheels of the sliding frame engage. Mounted upon and engaging with this bed-frame is a sliding frame, similarly braced, consisting mainly of t WO steel bars, upon which are mounted, at the rear ends, one double 5 in. X rq in. engine, from which power is transmitted through straight gear and worm wheel to the melt, by means of the sliding frame is fed forward. the front end of this sliding frame is mounted the cutter-bar, held firmly by two solid steel times, with suit able brass boxes. The cotter-bar contains steel bits, held in place by set-screws. When the cutter-bar is revolved, these cutters or bits cover its entire face. The cutter-bar is revolved by an endless curved-link steel chain from the driving-shaft. and siinultaneously advanced by the above mechanism into the coal or other material, to be undercut to the desired depth.