DRILL (from Dutch. Ger. drillen, to drill. colon-0441 ultimately with -1S. pyr,han, to bore, Eng. 'brim. in the broadest meaning of the a drill is a tool used in boring or making holes in metal. bone. ivory, wood, etc. Drills for boring wood are described under Boraxc Al unisEs. Rock drills. or rock-drilling inaehilbs, are a separate class of tools, and are described scparattdy below, Drills for metal. bone, ivory, (•c.. are made in several forms. One form con sists of a square steel bar. flattened out at the mining end. •his end is brought to an angular point like a spear-bead, and the cutting edges forming the angle are beveled in opposite direc tions. Those Which have a projecting pin in the centres and chisel-shaped cutting edges on each side of the pin are called 'centre-bits.' There are various contrivances by which the drills are made to revolye. For drilling iron, steel, and large brasswork. the drilling machine (see 'AIETAI. Woltgl MACUINERY) is eommonly used. The best and most generally used drills for small boring are called drills, which have many advantages over the fiat drill- described above. Twist drills are made from steel rods of uniform diameter throughout their length. the rod two spiral grooves are cot, each starting at the cutting edge at opposite points. At the and of the drill the grooves almost meet in the centre of the rod, hut grow shallower as they continue. The cutting edges are ground on the end of the rod and the borings eseape through the grooves, which constantly carry them away from the cutting edge, thus preventing clogging.
Ro•': PalLt.S. These may be divided into two Lenoral etas t• —viz. 11:111d drills and power drills. Briefly described. a hand drill is a bar of steel having a chisel shaped end or cutting edge. The simplest form of hand drill is worked by one man. who holds the drill in one hand and drives it with a hammer wielded by his other hand. A more efficient method of work how ever. where one mall holds the drill and another sw ings the hammer or sledge. Another form of hand drill, called a churn drill, consists of a long heav• bar of ste, 1. which is alternately raised and dropped by the workman, tints cutting a hole by rep, ate.) impacts. In drilling by hand, the workman holding the drill gives it a partial turn on its axis betwet n strokes, in order to prevent wedging and to Ott r a fresh surface to the cut ting edge. ‘Vlit n the conditions are such that use can be Made of them, it is nearly always preferolde use pom et* all Of their greater Igf 11,1r:ohm and greater economy of work.
PoWi R llmt I Is arc worked by direct steam pressure, t r Its air generated by t-teaut or water pow( r, and stored in re•eiver4, from w. Nth it i- led to the drills through iron pipes. (See Ain Court:1:550as.) There are a great variety of special forms of power drills, but they can nearly all he grouped in one of two classes: (1) r•ussion Aril!.', and (2) roiary
drills. The first American percussion drill was patented by .T. Couch, of Philadelphia. I'll., in 'Mardi, 1849. in .Nlay of the same year, 'Mr.
doseph W. Fo•le, who had assisted Conch in developing drill, patented it percussion drill of his own invention. The Fowl' drill was im proved by 31r. Charles Burleigh, and was tint used in the lloosac Tunnel. (See TUNNELS.) in Europe, Carib patented a drill in France. in October, This invention was soon followed by Others; but it was not until Sommeiler's drill, patented in 18.i; and perfected in 1S111. was used on the Mont Cenis that the problem of the per cussion drill was practically solved abroad. Sump that t ire drill patents have been taken 1110 in both _krtierica and Eu rope.
A percussion drill consists of a cylinder in which works a piston carrying a long pis ton-rod., and which is support ed in such a manner that the drill clamped to the end of the piston - rod alternately st rikes and is from the rock as the piston reviprocates back and forth in the cylinder. :\leans are provided by which the piston rod and drill turn slightly on their axis after ea•ll stroke, • and also h• which the is put forward or advanced as the depth of the hole in creases. ..ks previously stated, t here are Various special forms of percussion drills, and they differ from each other in the net hods by which the valve is operated. _111 of these drillswork eitheryvith direct steam pressure or with compressed air. Fig. I is a sect ion showing t he interior construe t 44 it common form 44 percussion drill to be operated by steam or compressed air. The steam or air is admitted at A to the chest. II. Prow It the slide valve, U. by moving back and forth ad mits the steam or air behind tirst one end and then the other of the long-barred piston, I). This slide valve is operated by the three-arni rocker, E. which is swung to fro by the movement i110 listed. ‘VOrk:11111' permission drills operat ed by electricity are built, lint so far they do not scene to have been able to compete commercially with the older forms. Fig. 2 shows sections of ele•trie drill which has been used to some CX t1 nt. Tin' drill is operated by a dexibie shaft loan a horsepower portable electric motor. This shaft is attached to ;,1 bi.V4•I gear (Irk lug II A, which passe. through the drill casing. The crank-pin works in the slotted hori zontal arm of the belberank lever It. which is mounted on a shaft joornaltil in the The vertical arm of the bell crank straddles the drill rod, and is titled to trunnions on at casting which slide- on the rod. Between this and the collars on the rod are coiled springs through which the power is transmitted for movement ? f the arm in each direction. .At the heel of the rod is a rifled section or rotchet-rod working in a rifled nut, by which the rotary movement is given to the drill-bit.