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Bore bits are cutting tools to produce holes in wood. Normally the bore bit is rotated around its axis. During such rotation it advances in axial direction. The wood to be removed must not be squeezed off or torn off but be removed by a clean cut. A bore bit consists of various parts (see Fig. 1).
Figure 1 Bit
1 square tang, 2 shang, 3 chip-removing screw, 4 pre-cutters, 5 brad point, 6 cutting edge
- The chip-removing screw presses the cut chips out of the bore hole.
- The parallel shank carries the cutting edges and the drill screw.
- The square tang is chucked in the jaw chuck of the bit brace.
- The brad point serves for exact location of the bit in the centre point. Bits intended for boring of holes vertically to the board plane have a very small brad point. Brad points of bits for boring of holes parallel to the wood grain have a draw-in thread.
Figure 2 Bore bit head
1 brad point, 2 draw-in thread
- The cutting edges (also called cutters) cut the chip between the brad point and the pre-cut circumference of the bore hole.- Compared to the cutting edges, the pre-cutters (also called pre-cutting edges) are in advanced cutting position and cut the wood grains already before the chip is removed by the cutting edges.
Most bore bits are held in and rotated by means of a boring appliance, i.e. an electric hand gun drill or a mechanical bit brace.
Figure 3 Bit brace
1 steel sweep handle with chuck, 2 ratchet, 3 supporting handle
The bit brace consists of a steel sweep handle with chuck, a supporting handle and a ratchet.
The ratchet is used for holes which are accessible from one side only and where a full rotation of the steel sweep handle is not possible. It is provided with idle gear for clockwise or counterclockwise rotation, which can be set.
The chuck serves for holding the bore bit.
What are the parts of a bore bit?
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What is the advantage of a bit brace with ratchet?
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