HOME CLINIC; Drills, Bits and Their Many Uses

A DRILL, either electric or hand, and an assortment of drill bits are a necessary part of any tool kit. For general tasks, it's best to acquire a number of twist drills (sometimes called Morse drills). These bits are essentially steel rods with two helical grooves or flutes running about two-thirds of the length. The remaining one-third, called the shank, is the part that is chucked into the drill..

Twist drills are sold singly or in sets. The sets usually have 10 bits ranging in diameters from 1/16 inch to 1/4 inch in increments of 1/64 inch. Smaller bits are available, but their diameters are designated in whole numbers representing wire gauge sizes.

The length of a bit varies with its diameter. Smaller bits are about 1 1/2 inches long, while the larger diameter bits are about 4 inches. It is possible to buy even longer lengths, up to 12 inches. These drill bits are called electrician's, or aircraft, drills and are designed to drill holes in hard to reach places.

In most cases, the size of the drill is limited by the chuck capacity; so a 1/4-inch drill cannot accept any bit larger than 1/4 inch. There are reduced shank bits that have a shank diameter smaller than the cutting diameter. With these it is possible to chuck a 1/2 drill bit into a 1/4-inch drill.
Twist drills are designed for boring holes in metal and other hard materials. Always use bits made of high speed steel, not carbon steel, for drilling these materials. The workpiece should be secured in a vise or clamped down on the workbench. Mark the center of the hole with a punch. This will create a small dimple or recess that will guide the drill and keep it from wandering off the mark. Cutting large holes can be difficult because the drill has to remove a lot of metal. It's easier to drill a pilot hole first, then enlarge it with a larger drill bit. Ease up on the drill pressure just before the bit breaks through the work or it may bind and damage the workpiece.
It is important to control the speed of the drill when boring into hard materials. Drill speed will vary with the size of the drill and material. As a general rule, use slower speeds for hard metals (steel) and/or large diameter drills, and faster speeds for softer metals (brass, copper) and small drills.

Drilling through metals produces friction that can cause the bit to overheat; for this reason it's important to lubricate the drill bit. Use light machine oil when drilling through steel or wrought iron. Use kerosene or turpentine when drilling aluminum. Cast iron can be drilled dry. Brass, copper and bronze can also be drilled dry, although some machinists like to lubricate the bit with paraffin.

Boring holes into wood is a lot easier than drilling into metal. Still, the standard twist drill has a tendency to chew up the surface somewhat as it penetrates into the wood. Some wood workers avoid this problem by regrinding the cutting angle from 59 degrees to 45 degrees, but most cabinet makers prefer to use special drill bits called dowel, or brad-point, bits. At the outside edge of the bit are two spurs that literally slice through the wood fibers to produce a clean hole. These bits are available in diameters from 1/8 to 1/2 inch.
For boring larger holes, the classic woodworker's tool has always been the brace and bit. The brace is a simple hand tool that has a shaft with a chuck at one end and a head at the other. The handle is in the center of the shaft. Turning the handle rotates the chuck so the bit bores into the work. Feed is controlled by applying pressure.