A light crank-brace for drilling small centre holes and enlarging conical holes in work to be lathe-turned is made of three principal pieces: one piece consists of the circular plate which is to be in contact with the operator's hand, breast, or thigh ; another piece is the crank part; and the other portion is the boss that will contain the end of the drill to be rotated with the brace. The boss portion is forged of a piece from the side of which an end is fullered and reduced until small enough to be welded to the crank piece. This crank is forged of straight iron, and the plate is riveted to a couple of small arms, or to a thin flange that belongs to the pivot-bearing, this bearing being that which sustains the pressure while the tool is in use.

The cone-driller shown in the brace denoted by Fig. 276 is provided with either a square taper end or with a conical end to fit the boss. The forging of such a coner is effected with a piece of round steel about as thick as the thickest part of the intended tool, and after being tapered for the hole in the brace, and reduced in the mid-part, the tool is lathe-turned and coned, and also lined to indicate the place for the cutting edge; at this stage the implement appears as in Fig. 476, and to produce the semi-conical form it is reduced until a cutting edge is formed at the centre of the tool's rotation; this edge is shown in the Figure by the dotted lines. The hardening and tempering of a cone-driller is somewhat similar to that for a dotting punch or a drill, and consists in heating the cone, and also nearly the whole of the other portion of the tool, to redness, and moving about in the water until cold that portion which is to be hard; when hard, the cutting end is cleaned to show the colours. For a cone-driller the tempering is effected with the heat in the tool until a dark brown is seen, at which moment the entire tool is cooled in the water to prevent the end becoming too hot, and thereby too soft.

Scriber-Blocks

Scriber-blocks, whether of wood or of iron, are made in a great variety of forms, the precise shape adopted depending on the taste and skill of the designer. To make one that consists of a circular or rectangular base plate, and a vertical standard to be fixed to the plate, it is usual to screw a hole in the plate, and to screw one end of the standard to fit the hole. A block of this class is shown by Fig. 477, the pillar or standard being shown distinct from its plate. In the upper part is seen a slot to hold the fixing bolt that tightens the scriber while being adjusted; this slot is made by drilling and filing, and the arrangement for causing the bolt to grip the scriber is shown in Fig. 478. A tall block, which is in the form of an el-square, is very firm on its base if the long blade is of wood and the pedestal of iron or other metal; a wood blade several feet in height may be thus used without causing the block to be unsteady. To avoid inconvenience through the wood blade getting loose in its joint gap, it is necessary to bore a hole through the pedestal and blade, and tighten them together with a small screw-bolt.

Vee-Blocks

The most durable vee-blocks are those of steel, the second quality being those of iron. A couple of vee-blocks that are not required to be very firm on their bases, and may need much handling, may be made fight by making them of cast iron or steel, and forming a hollow at each end at the time of casting. Blocks of this form are denoted by Fig. 479. The simplest mode of making vee-blocks consists in forging them to very near their finished dimensions. To do this, the vee-gaps are made while the work is hot on the anvil, and the cutting commences by first punching a hole at the intended bottom of the gap; after this the superfluous piece is cut out with chiselling. When roughly prepared, a paring chisel is required to shape the gap sides and other sides of the work, and the tool is completed by smoothing in a small planing-machine or shaper. Vee-blocks that are smoothly forged or cast need no planing for many sorts of work, the small amount of finishing which is necessary being effected with chipping and filing. When a couple of vee-blocks are required to be very smooth and similar to each other, both are planed together on the table of the machine.