Drill bit

Drill bits are the cutters of drill tools. Bits are interchangeable, meaning that they can be removed from the end of the drill, either to replace a worn part or to change the size of the part.

Brace drill

The brace drill bit is optimised for drilling in wood with a hand brace. Many different designs have been produced.

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The centre of the bit is a tapered screw thread. This screws into the wood as the drill is turned, and pulls the bit into the wood. There is no need for any force to push the bit into the workpiece, only the torque to turn the bit. This is ideal for a bit for a hand tool. To pull the bit from the hole, either the female thread in the wood workpiece must be stripped, or the rotation of the bit must be reversed.

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The edge of the bit has a sharpened spur to cut the fibres of the wood, as in the lip and spur drill. A radial cutting edge planes the wood from the base of the hole. In this version, there is no helix to remove chips from the hole. The drill must be periodically withdrawn to clear the chips.

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Some versions have two spurs. Some have two radial cutting edges.

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Brace drill bits are made of relatively soft steel, and can be sharpened with a file.

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The drill bit shown was made sometime before 1950, and still works to drill holes in 2005. It drills a hole of diameter 3/4 inch.

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Image:drill brace.jpg|3/4 inch brace drill bit

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Image:drill tip brace.jpg|3/4 inch brace drill bit tip detail

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