Drills for different jobs
without a bit is like a bow without an arrow. The better the drill, the better the results. Like saw blades, drill bits come in many varieties and are suitable for drilling through almost anything. Depending on your needs, you may wish to have a few different types of drills on hand, but a good starter set should consist of at least a small index (maybe ten bits) twist drill and a set of spade bits (maybe six pieces ).
. These bits are exactly what their name suggests: each steel shaft terminates in a spade blade. The shovel is flat with a pointed point in the middle. This point acts as a guide, centering the hole and leading the way, but most of the drilling is actually done by the ground cutting edge at the shoulder. Don't try to cut metal with this. Spade bits work well with wood, plywood, and some plastics, and can cut quickly with amazing precision. Only use them at high speeds to prevent the bit from becoming lodged in the workpiece and from trying to get the bit out of your hand. Spade bits are between a quarter of an inch and an inch and a half in diameter.
twist drill. Twist drills were invented by a man named Morse, and some machine shop types refer to twist drills as Morse drills. Twist drills have a cylindrical steel shank and a pointed point. A pair of helical grooves (sometimes called chip channels) run along two-thirds of its length, wrapping around the handle like the stripes on a barber's pole.
The cutting edge (called the lip) is located at the tip of the notch where it meets the workpiece. The chip flutes do not drill the hole themselves, but clear debris from the hole to prevent the drill from jamming or being slowed down by waste material. The tip of most twist drills is at a 59-degree angle from the axis so that they can effectively cut through metal; of course, they will cut wood as well. Carbon steel bits are designed for drilling wood and should not be used for cutting metal. Twist drills typically range in size from one sixteenth of an inch to half an inch. Most twist drills larger than a quarter inch have a reduced quarter inch shank.
Brad drills. Angle drills are designed for cutting wood and are a cross between a spade drill and a twist drill. The shaft of the drill bit is similar to a twist drill, and the fluted chip channel spirals around the shaft. Most of the cutting is done at the edge of the channel, but the hole actually begins with a smaller diameter corner head (or spike) that introduces the shaft into the hole. Two additional spurs on the outer edge of the bit help keep the bit in line. Angle drills usually cut deeper channels than twist drills to remove wood chips.