Twist drills are the most widely used of all drill bit types; they can cut anything, from wood and plastic to steel and concrete. They are most commonly used for metal cutting, so they are usually made of M2 high-speed steel. Twist drills up to about 1/2" in diameter are not only the cheapest of all drill bits that can be used by woodworkers, but also provide the widest selection of sizes. Although they are designed for cutting metal, they can also work well on wood. Work well, if sharp. This usually means that they are not used to cut hard materials such as steel.
A twist drill is a metal rod with a specific diameter, and most of its length has two, three, or four spiral grooves. Two-blade drills are used for primary drilling, while three-blade and four-blade drills are only used for enlarging or punching holes in production situations.
The part between the two grooves is called the web, and a point is formed by embossing the web to an angle of 59° (including 118°) to the axis of the drill bit. This creates a slanted cutting edge on the edge of the flute, called the lip. Twist drills are very inefficient at this point because the web leaves little exit space for debris (called chips), and the surface velocity at this point is low compared to the periphery. For this reason, a good solution for drilling large holes is to drill 1/4" or smaller first, and then use a drill of the desired diameter.
