TOOLS FOR DRILLING. 99 



is seen to be precisely in the centre, the punch is placed again upon 

 it and the cavity made deeper by a harder blow ; if the centre has 

 been missed, the small mark will not be in the way of placing the 

 punch now upon the exact spot by the side of it, where the mark is 

 to be made. The axis, when thus prepared, is placed into the 

 hands of a turner, in order to have a piece of wood firmly fixed upon 

 it, which is to be turned into the short cylinder with fillets at both 

 ends, which forms the pulley. One end is now made into a conical 

 point, not so sharp as that of the punch ; in using the drill- stock 

 this point rests in the cavity v of the breastplate. This is a plate of 

 iron about 2 or 3 mm thick, and a few centimetres square, fixed with 

 a few nails to a small wooden board, 2 cm thick, 8 cm broad, and 10 em 

 long. The drill-stock is turned by means of a drill-bow ; this is 

 made of a piece of cane, about 12 mm thick and from 60 to 80 cm 

 long, and a strong piece of catgut, which is attached to the piece of 

 cane by boring a small hole at each end of it, passing the extremity 

 of the string through the hole and fastening it with a knot, much 

 in the same way as in an archery bow. The string must be rather 

 loose ; when the bow is to be used, one end of it is placed against 

 the table while the other is held by the hand, and the string 

 is passed round the pulley of the drill-stock in a single loop, or 

 with a ' round turn.' The cylindrical hole at the other end of the 

 axis, for the reception of the drills, is pierced by the double-cutting 

 irill, shown in fig. 70 at G and H in two positions, while / gives a 

 view of the point if the drill is held horizontal in a line with the eye. 

 The hole must be about 10 or 12 mm deep, and of the same diameter 

 is the shank of the drill, 3 or 4 mm . A piece of steel wire of this 

 liameter, and 5 or 6 cm long, is well straightened in the vice, bend- 

 ng it with the help of the tail- vice and using the hammer where 

 lecessary. This is filed away for a length of about 2 cm at one end to 

 ; i very little less than half its thickness, as shown at H : if the drill 

 s filed away only just to the middle, it will make a larger hole than 

 s intended. At a the angle should be shaped by filing with a rat- 

 ail into the curve shown in the figure ; if left angular, the drill is 

 iable in the process of hardening to crack at that place, and breaks 

 'asily. Two small facets are then formed at the end, as shown in 

 he figure ; the facets must be perfectly equal, or the hole will 

 >e larger than required. The drill, after being hardened, is clamped 

 torizontally in the vice, and about 3 cm of the cutting end are allowed 

 o project. 1 A small cavity having been made previously with the 



1 If the position of the vice is inconvenient, the drill may be fixed in a 

 ail-vice, and this in a proper vice ; it will thus be always possible to direct 

 he drill towards the operator. 



H 2 



