100 TOOLS FOR DRILLING. 



punch in the centre of the face of the axis, where the hole is to be 

 bored, the string of the bow is looped round the pulley, the pointed 

 end of the stock is inserted in the cavity of the breast-plate, into 

 which a drop of oil is poured, and the plate pressed against the chest, 

 while the point of the drill is placed in the mark or cavity made at 

 the other end with the punch. Care being taken that the axis oi 

 the drill and the drill- stock are in the same straight line, the bow is 

 moved with the right hand to and fro, while the stock is pressed 

 forward by the chest upon the drill, which -enters slowly into 

 the axis of the drill-stock. The chips of metal must be frequently 

 removed ; for this purpose the drill must be withdrawn from the 

 hole. When the hole is bored to the required depth, a square 

 notch is filed just at the inner extremity of it, down to half the 

 diameter of the drill- stock ; the drills are also filed away to one 

 half for a distance of about 6 or 8 mm from the end, so as to slide 

 into the drill-stock in the manner shown in fig. 70, B and C. 

 The drills are thus prevented from revolving, because the flat end 

 of the drill rests upon the flat surface of the notch in the axis oi 

 the stock. Work to be drilled is hereafter always fixed in the vice. 



The usual form of drills is shown in fig. 70, B to F. D is a view ol 

 the broad, E of the narrow face, F of the end. The greater portion 

 of the length should be narrower than the cutting extremity ; foi 

 the stronger kinds the wire is softened by heating and flattened al 

 the end by hammering, the remainder being left round ; the weakei 

 kinds are thinned by filing. It is best to make them rectangular 

 taking away on each side as much as would give them on the nar 

 rower side the appearance shown at (7, and then curving off th( 

 narrow side to the form at B. The point is formed by two facets filec 

 somewhat obliquely against the sides, so that if the broader side o 

 the drill, JD, be held before the eye, the point uppermost, the righ 

 facet must slope to the side seen by the eye, while the left mus 

 slope towards the opposite side ; if the narrow side, ^7, be held be 

 fore the eye, the facet seen must be inclined to the left side. Th 

 long narrow faces which run from the point of the drill to the slianl 

 should also be somewhat oblique, as shown in D and F. New drill 

 may be improved by being sharpened upon a hone, placing eacl 

 facet flat upon it and moving it in this position to and fro, so as no ' 

 to grind the cutting edges. Blunt drills should be made soft agai: 

 and prepared anew : this will require less time than that lost i: 

 using a bad tool. 



The holes for screws should first be made a little too small an 

 then widened until the taper-tap will just go in a little way. Fo 

 widening holes a tool called a rimer, fig. 71 (page 102), is used ; thi 



