Twist drill bits are among the most common types of bits. Commonly used for drilling wood, plastic or metal, twist drill bits typically range in size from 1/16 of an inch to an inch in diameter (or even larger in commercial applications). Twist drill bits are used at high speed for woodworking, but are turned much more slowly when drilling in metal to keep them from heating excessively.
The shank of a twist bit is the portion that locks into the drill chuck. On bits of up to 1/2 inch in diameter, the shank is typically smooth, and the same thickness as the bit size. On bits larger than 1/2 inch, the shank may be tapered or narrower than the bit width.
The point of a twist drill bit is typically ground so there are two chisel-like cutting edges extending out from the point at the centre of the tip. For wood cutting bits, the point is usually at a steeper angle than on metal cutting bits. This allows the bit to cut more aggressively through the wood.
Twist drill bits typically have two or more flutes, deeply-cut grooves that spiral upwards from the bit point. These flutes take the cut material and lift it out of the hole being drilled. Without the flutes, the drill bit wouldn't be able to eject the cut material.
Drilling Wood and Plastic
When drilling wood and soft plastic, the drill bit can be turned at a high rate of speed, allowing the bit to drill through the material quickly. Softer materials don't heat the bit much, so no lubrication is needed.
When drilling into metal, the point of the twist drill needs to be a little less flat and the drill should spin much slower than when cutting wood or plastic. This allows the bit to make thin cuts through the metal, and helps keep the bit from binding. Applying a light utility or three-in-one oil to the hole as it's being drilled will help the drilling process, and keep the bit from overheating.