BORING 455 



carrying the cutting" bar. The piston-rod g 1 passes through a stuffing box in the 

 cylinder, and takes a bearing at tho end of the frame of the drill as shown at f ; and 

 as the rod on tho front side of tho piston also passes through a stuffing box, tho chief 

 moving part of the machine is supported at three places in its length. Upon tho 

 piston-rod g- an enlargement, &', k' 1 , k 3 , is made -with two conical faces ; the valvo 

 tappets 1 1' are in contact with these faces, and the reciprocating motion or the piston- 

 rod imparts to them the necessary motion for actuating the valve. Tho angle of the 

 tappets can be adjusted at will to regulate the distribution of the steam or air. 

 Between the sloping or conical surfaces of the enlargement of the piston-rod there is a 

 straight length k 3 , in which are cut ratchet-teeth in an oblique direction around the 

 surface ; these teeth como in contact with a grooved bar m, the grooves m! being cut 

 to correspond with the teeth in k 3 . In the frame of the drill is formed a recess, in 

 which a spring m 2 is placed, the centre of the spring pressing against the back of the 

 grooved plate m. At tho forward stroke of the piston, tho enlargement k 3 pressing 

 against m depresses.it, forcing it into the recess ; but at the return stroke, the teeth of 

 k* engaging in the grooves of m, give it a rotating movement to the piston-rod, 

 piston, and cutter bar, so that a slow and constant turning of tho cutter is effected. 

 Tho amount of rotary motion imparted during each stroke is about one-sixteenth of a 

 revolution. 



The automatic feed arrangement for keeping the end of the cutter in contact with 

 the rock consists of a double threaded screw, with a key way in it, as shown, extending 

 from end to end of the machine, the rear bearing being formed by a bracket. On the 

 outside of the cylinder a, two stops o 5 are cast, and between these stops is placed a 

 nut n', which is prevented from turning by being made with a flat side bearing 

 against the outside of the cylinder a. Through this nut the screw n passes ; fitting 

 into the ratchet p' is a second ratchet q, with an arm $ that is attached to the tappets 

 1 1', which gives a reciprocating motion to the ratchet q, and a constant revolving 

 motion to tho sleeve p ; the key in which drives the screw, which turns the nut n' 

 and with it the whole drill, whilst the screw travels freely through the sleeve p. 

 By this means a constant and regular feed is obtained. The end of the screw at o' IB, 

 however, made square for the reception of a lever, by which tho automatic feed can 

 be replaced by a hand movement. The cutter bar is made adjustable by means of a 

 screw thread and nut, the face of tho nut against the key being grooved, so that when 

 it is screwed up tight and the key driven in, there is no possibility of the key shaking 

 loose and the cutter becoming unfastened. 



The machine of the size ordinarily used for quarry work or open cutting weighs 

 about 160 Ibs. A smaller, and for many purposes a still more convenient form is 

 manufactured, which can be handled by one man. 



With a steam pressure of 75 Ibs. to the inch, it will drill as a maximum, a 2^inch 

 hole to a depth of 10 inches per minute in Aberdeen granite ; but the average duty may 

 bo estimated at from 6 inches to 9 inches per minute, and the number of strokes from 

 500 to 1,000. 



For sinking shafts the machine is mounted on a column placed crosswise in tho 

 shaft, and fixed rigidly by the telescopic and screw adjustment above mentioned, from 

 which column any required direction may be readily given to tho boring tool, or tho 

 drill may be mounted upon adjustable stand or frame, as is designed for quarry and 

 open work. 



For driving tunnels where one or more machines may be worked against the face, 

 tho machines are mounted upon moveable and adjustable columns, supported upon a 

 carriage moved upon rails. 



In reference to this drill Sir George William Denys states as follows : 



(1) Weight of machine without stand, large size l cwt., small do. 1 cwt. (2) 

 Length of drill 38 inches. (3) Diameter of piston 5 inches, length of stroke 2 to 4 

 inches. (4) Strokes per minute, 500 to 1 ,000 ad libi turn. (6) Pressure required 25 

 to 75, average 50 Ibs. (6) Advance of drill, automatic or by hand ; but where only 

 one machine is working the hand is preferable, for it obliges the miner to pay 

 attention and see that the drill advances regularly. (7) The nature of tho stone 

 varies ; we have lime, chert, and grits of every degree of hardness. (8) Diameter of 

 water-wheel 38 feet or 28 feet would have done as well ; bucket 4 feet wide ; breadth 

 of water trough 2 feet ; depth of water varies with the supply from 3 to 8 inches. 

 (0) Compression wot, a half-inch pipe carries the water up the level, and squirts the 

 water with great force into the holes, and keeps them quite clean. (10) Dimensions 

 of level 6 feet high clear of the rails, and about 6 feet wide. (11) Tho air-pipes are 

 2 inches in diameter, butl think 1 inch would suffice. (12) The level forehead is now 

 nearly 400 fathoms from tho compressor; tho ventilation excellent, the air being as 

 good inside tho mine as out, 



Some special measurements and particulars of this drill are ns follow : Diameter 



