Drill Bits for Different Jobs

An electric drill without bits is like a bow without arrows. And the better the bit (or arrow, I suppose), the better the result.

Like sawblades, drill bits come in lots of flavors, suited to drill through just about anything. Depending upon your needs, you'll probably want to have several different types on hand, but a good starter set of drill bits should include at least a small index (perhaps ten drills) of twist drills and a set of spade bits (perhaps six pieces).

Twist Drills. Twist drills were invented by a fellow named Morse, and some machine shop types refer to a twist drill as a Morse drill. A twist drill has a cylindrical steel shank and a pointed tip. A pair of helical flutes (sometimes called chip channels) run along two-thirds of its length, twisted around the shank like the stripes on a barber's pole.

The cutting edge (called the lip) is at the tip where the mouths of the flutes meet the workpiece. the flutes themselves do no drilling, but clear the debris from the hole to prevent the drill from binding or being slowed by the waste.

The tips on most twist drills are ground at a 59-degree angle to the shaft so that they will cut metal efficiently; naturally, they'll cut wood, too. Carbon steel bits are ground specifically for drilling wood and should not be used to cut metal. Twist drills are commonly sold in sizes ranging from a sixteenth of an inch up to half-inch diameters. Most twist drills larger than a quarter inch have reduced shanks of a quarter inch.

Spade Bits. These bits look like their name suggests: Each steel shaft terminates in a spade-shaped blade. The spade is flat, with a sharp point at the center. The point acts as a guide, centering the hole and leading the way, but the bulk of the drilling is actually done by the honed cutting edge at the shoulder of the spade.

Don't try to cut metal with this one. Spade bits are for wood, plywood, and some plastics, and cut quickly with surprising precision. Use them only at high speeds, to prevent the bit from catching in the workpiece and the drill from trying to wrench itself from your grasp. Spade bits are found in the range between quarter inch in diameter to one and a half inches.