BITS are of various kinds, depending on their use : Shell BITS are used for boring wood, and have an interior cylindric concavity for containing the core.
Centre BITS, are those which run upon a centre in the middle of the breadth ; one extremity is formed into a cutting edge, which cuts the wood across the grain around the cir cumference, and the radius on the other side of the centre contains a cutting edge, the whole length of this radius, and projects forward from the face of the bit, so as to take out the core, which in the act of boring forms a spiral.
The use of the centre-bit, is to form a large cylindric hole or excavation, having the upper point of the axis of the cylinder given on the surface of the wood. The centre of the bit is fixed into this point, then placing the axis of the stock and bit in the intended direction, the head being placed against the breast, turn it swiftly round by the handle. and the core will be discharged by rising upwards. Centre bits are of different diameters.
Countersinks, are bits for widening the upper part of a hole, in wood or iron, to take in the head of a screw or pin, so as not to appear above the surface of the wood. Counter
sinks have from two to twelve cutters around the surface of a cone, which contains a vertical angle of ninety degrees. Countersinks for iron have two cutting edges, and those for wood and brass, the greatest number.
Rimers, are bits for widening holes, and for this purpose are of a pyramidal structure, having their vertical angle about 3:1 degrees. In the use of rimers, the hole must be first pierced by means of a drill or punch. The operation of a rimer is rather scraping than boring. Rimers for boring brass, have their horizontal sections of a semicircular figure, and those for iron, polygonal.
Taper Shell Mrs, are conical within and without, with their horizontal sections crescent-lonned. The use of shell bits is to widen holes in wood.
Besides the above bits, some stocks are provided with a screwdriver, for sinking small screws into wood with greater rapidity that could be done by hand.