Feb. 20, ISSo.] 



♦ knowledof: . 



163 



be obtained of tbe above-mentioned firm. In workinj; 

 with this tool, tbe material is placed between the jaws, of 

 which one may be moved to and fro with the baud and 

 pressed up against the matt rial. The material is then 

 secured by turning a lever handle, to which is attached au 

 eccentric cam, which, in turn, tightens the bar to which the 

 movable jaw is attached. 



E.x. XXVIII. — Fig. 9 illustrates a " hand " vice, which 

 is very useful for manipulating small work, such as the 

 heavier forms above referred to would be unsuited for. 



What is drilling! A process for boring holes in or 

 through metals and other substances. This is accomplished 

 by means of a " drill," cousi.vting of a suitably pointed 

 and sharpened piece of steel wire or rod, which is made to 

 revolve more or less rapidly against the material, and so to 

 cut a hole of the required size and depth. Two things are, 

 therefore, essential, viz., the drill and the apparatus for 

 revoh-ing it, which is called a " drill-stock." 



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Fig. 9. 



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FiV. 10. 



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Ex. XXIX. — The drills we s-hall have occasion to use 

 ■will be only small, their size ranging from J^ to j\ of an inch 

 (measured across the broadest part of the cutting edge), 

 consequently we shall only deal with such processes as are 

 involved in making and working wiih them. Fig. 10 illus- 

 trates a series of drills of useful sizes, made from a piece of 

 the best bright cast tteel wire (B.W.G., Xo. 9, about —- 

 inch in diameter), obtainable in foot-lengths, at any tool- 

 shop. The steel mentioned may be relied upon as being of 

 the necessary quality. One notable distinction in drills is 

 that some are smaller than the wire from which they are 

 made, while others are larger. Tlie convenience resulting 

 from making the several drills from a single-size wire is 

 that they will all fit one and the same drill-stock. To make 

 a drill smaller than the wire, cut off a piece of wire about 

 2 inches long, with the aid of the edge of either 

 of the files referred to in Ex. XXIV. Hold one 

 end of the piece of wire in the hand-vice (Ex. 

 XXVIII ), and reduce the thickness of the free end 

 for about half-an-inch of its length. This is done by 

 placing it in a groove cut in a piece of hard wood held in 

 the table-vice, and then with the left hand revolving the 

 wire inwards (and, of course, the hand-vice holding it), 

 filing outwards at the same time with the right hand, and 

 applying equal pressure to the file throughout the opera- 

 tion. The part filed should be reduced to a slightly 

 taper point, the point being made smaller than the hole 

 which it is intended to drill. The point is then flat- 

 tened out, by placing it upon an anvil or block of 

 iron, and spreading it with a hammer to a width 

 slightly greater than the diameter of the intended hole, 

 after which the point is filed at right angles to the plane 



of the " blade," to an angle not exceeding 100". The 

 sharpness of this angle will, however, depend upon the 

 hardness of the material to be worked ; for example, the 

 angle for cutting brass would be considerably sharper than 

 that adopted when cutting steel. It only remains 

 now to provide the cutting tdges. This is done 

 by holding the drill in the left hand and filing 

 the narrow sides of the flattened portion to a small 

 angle (not exceeding 4.")"), filing downwards, so as to leave- 

 the higher edge nearest the body. The jxiiiit previously 

 made is simil;irly dealt with. The size of this last angle 

 depends very much upon the kind of work in hand, and 

 can only be determined after practice. To lay down a 

 hard-and-fast rule would be impossible. When the cutting 

 end is to be wider than the wire, heat one end of the 

 wire to a red heat and flatten out on an anvil or iron block 

 to the required width. There is a limit to this widening, 

 owing to the very obvious fact that an increased widtl; 

 involves a reduced thickness. Having been ])roperly 

 flattened, the cutting edges are produced in a way similar 

 to that adoptfd for the previouslj -described smaller drills. 



Having made the drill, let us now turn our attention to- 

 the liardening and ti mpering processes. 



E.x. XXX.- — To accurately define "hardening" is a 

 matter of impossibility. At present we can only speculate. 

 The recent researches of Prof. Hughes (to which reference- 

 has previously been made in these pages) would seem to 

 indicate that the super tioial molecules or particles become, 

 during the process, rigidly associated one with the other, 

 but how this comes about or how it is maintaintd it ia 

 difficult even to imagine. The hardening process consists 

 in raising the steel to a dull red-heat, and then immediately 

 chilling, and thereby hardening it in water or oil. We 

 often hear of workers who, with an air of mystery, show 

 us a solution which they would have us believe possesse.'-, 

 unusual qualities for hardening. We never yet, however, 

 came across a single solution which was in any way 

 superior to water or oil. With reference to the heating 

 it may be observed that when an ordinary coal tire is used, 

 it will be necessary to guard against over-heating or iiTe- 

 gularly heating the steel. These troubles may be avoided 

 by placing the steel within a piece of old gas-pipe, and 

 then heating both together. A uniform increase of tem- 

 perature is thereby ensured, while at the same time the 

 surface of the steel is kept clean. To complete the 

 hardening, the pipe is removed from the fire, and tbe steel 

 allowed to drop out of it into the water. If a gas blow- 

 pipe is at hand, the operation may be performed more 

 rapidly. First heat about half au inch of the cutting end 

 near the point of the flame to a dull red heat, and i)lunge 

 it in water. 



Hardening, however, is a process which renders steel 

 very fragile, but which may be overcome by tempering. 



E.x. XXXI. — Tempering is a jirocess for restoring the 

 tenacity to hardened steel. It consists in partially restoring 

 the softness of the metal, the degree of softness varyinj;- 

 with the quality of work to be performed. First clean the 

 flattened surfaces of the drill upon an oilstone or piece of 

 emery-cloth, care being taken not to touch the brightened 

 parts with the fingers, otherwise some difliculty will be 

 experienced in ascertaining when the proper degree of tem- 

 pering has been attained. To temper the diill hardened in 

 the gas- pipe, place it on a hot iron plate, allowing the cut- 

 ting end to overhang. In a very short time the overhanging 

 portion will be seen to assume a deep straw colour. It 

 should then be immediately dipped into water, when th-:; 

 nece.ssary degree of tempering will be obtained. The in:- 

 mersion in water prevents softening to too great an extent. 

 When the hardening has b';en perfoimcd with t! e aid of a 



