Makch 20, 1885.] 



♦ KNOWLEDGE ♦ 



2.1 



■whole length, in order that it may be able to sustain tlie 

 end pressure exerted upon it to cause it to bite the 

 metal being drilled, and at the same time to prevent its 

 bending. 



(?) The young worker is apt, if he thinks his drill Las 

 softened, to immediately proceed to re-harden and temper 

 it, but this should not be done unless it is really soft, for 

 a too frequent ajiplication of the process impoverishes the 

 quality of the steel. Drills so treated are rarely of any 

 real use. It may be mentioned that the prime cause of 

 softening is working the drill too rapidly — at a greater 

 speed, in fact, than the apparatus employed will permit, 



(_/") When drUliog steel, wrought-iron, or other hard 

 metal, the work must be done slowly, with more pressure 

 than is necessary for the softer metals, and with a good 

 supply of oil Should this fail, alter the cutting edges of 

 the drills, making their inclination somewhat less acute — 

 approaching, that i^, a liitle nearer to a flat edge. When 

 drilling brass or other soft metal, oil is not necessary. 



(9) The drill should be kept sharp. This may be done 

 by occasionally rubbing the cutting edges upon an oil- 

 stone. 



E.x. XXXVII. — In the event of the young electrician 

 not caring to make his own drills, he may buy them at a 

 very low figure. Messrs. Melhuish tt Son, of Fetter-lane, 

 E.C., supply them at Is. 6d. per dozen, assorted. I may 

 mention that I have received from this firm a box con- 

 tainiog forty-eight drills of sixteen assorted sizes with a 

 drill-stock. They are of tirat-class workmanship and in 

 every way commendable. 



Ex. XXXVIII.- — It not uufrequently happens that when 

 a hole has been drilled it proves a little smaller than is 

 required, in which case a handy little tool known as a 

 broach may be employed to enlarge the hole to the 

 required size. Fig. IG illustrates this piece of apparatus 



sss^^ 



-..C'J 



Vig. IG. 



very clearly. It may be procured at any tool shcjp. It 

 consists of a steel wire cut to a pentagonal section at d 

 slightly tapering from the tang or thereabouts to the point. 

 The shape of the point is clearly shown on the diagram. 

 The tang is cut square so that it can be held in a hand vice 

 or fixed into a wooden handle as shown. The broach illus- 

 trated is .3i in. long, but the length varies with the size, 

 ihe stronger ones being longer than the finer. To use the 

 tool, place the point in the drilled hole and rotate it gently, 

 using oil when woiking the harder metals (see E-x. xxxvi. _/.'). 



PILES AND FILING. 



This is a most important branch of the young worker's 

 labours, and requires some little attention. 



The majority of aspirants to mechanical skill seem to 

 agree in the difficulty they experience in their endeavours 

 to file flat ; but, if our young electrician will only set him- 

 self steadily to work to accomplish this much-to-be-desired 

 feat, he will speedily fitid himself master of the task. It is 

 simply a question of practice and attention. 



Ex. XXXIX — Let us suppose that it is desired to file, 

 or produce by filing, a flat surface. To do this, procure a 

 file longer than the material to be worked. Then take 

 hold of the hanclle by the right hand, placing the left on 

 the point of the tile. Then proceed to work the tool back- 

 wards and forwards, letting it pass over the full width or 



length of the surface V)eing filed at each stroke. It is with 

 thi.s view that a file longer than the nuiteriiil is recom- 

 mended. Every ellbrt must be made to keep an equilibrium 

 or balance between the action of the two hand.a, as the 

 file is moved forwards and backward.", more especially in 

 the forward stn^ke. Pressure should only be exerted in 

 this forward stroke, that is to say, the file should only bo 

 pcrmittt d to cut one way. As a matter of fact, th<^ teeth 

 of the tile are so shaped as to render it impossible to prt)- 

 duce a cut during the backward strike, which, at most, 

 can only pioduce a scratch, ^\'hen the metal being filed 

 liappens to be hard, there is a liability of spoiling tlie file, 

 if any attempt is made to cut during the backward stroke. 

 Xopiessureshould therefore be applitdduriiigthis movement. 

 By filing steadily and attentively, the hands will speedily 

 acquire the necessary degree of sensitiveness to enable each 

 to adjust its pressure in proportion to the other, as well as 

 the knack of maintaining a flat surface. The file should 

 always be moved in a straight line, more particularly when 

 administering the finishing touches. Curve! file-cuts are 

 an abomination. Care should also be taken to avoid short 

 and jerky movements. But let each motion be bold and 

 resolute, as though it were intended that something 

 must go. 



The student will do well to practise the art of filing on 

 odd pieces of metal, placed in a vice or other convenient 

 means for keeping them stt ady. 



New files should first be used en brass. A little u;e in 

 this way will biing them into good condition for iron and 

 other harder metals, but, when once so used, they are spoiled 

 so far as .softer work is concerned. A file, that is, which 

 has been used for cutting iron, will not work satisfactorily 

 on brass or copper-. 



It is often necessary, or rather one is often ccmpelkd, to 

 file with one hand. In such cases, there is an increased 

 tendency to produce anjthing but a horizontal surface. 

 Here, again, practice must be resorted to to obtain the 

 proper or requisite degree of efticiency. The material to 

 be filed may be laid on a piece of cork or wood, jilaced in 

 a vice, and worked with a small-size file held in the right 

 hand. Every effort must be made to | lace the file in a 

 horizontal position at each forward stroke, the pressuiti 

 applied being light. A sort of instirctive feelii g will, 

 after a little practice, indicate when '.he file is not workiig 

 right, and so enable the worker to adjust the pressure ai;d 

 force needed to maintain horizontal working. It frequently 

 happens that small articles may be held aganst the fore- 

 finger of the left hand while the filing i? performed with 

 the right. Success in this method of tiling is not difficult 

 to atta'n — less so, in fact, than when the material is laid on 

 the piece of cork or wood. 



Ex. XL. — Files are divisible into three classes, according 

 to the relative fineness of the teeth or cutting edges. They 

 are 



(a) Smooth, in which case the teeth are very fine indeed, 



(/j) Second-cut, a little coarser. 



(c) Bastard, or coarse-cut. 



Ex. XLI. — Files are made in six shapes, f ach of which 

 is obviously adapted to a particular speeii s of work. These 

 shapes are 



((/) Flar, in which there are two more or less wide cuttirig 

 faces parallel one to the other. One of the narrow faces or 

 edges is also provided with teeth. 



(i) Three-square (>hown in section in Fig. 5, page 10.3), 

 in which there are three flat cutting faces, each making eh 

 angle of 60^ with the others. 



(c) Square, in which there are four flat cutting faces at 

 angles of 90^. 



[(1) Half-round (shown in Fig. 4, page 103), in which 



