Types of Drilling Tools
Braces guide auger bits and drills. Attaching a screwdriver bit converts them into powerful screwdrivers. Drilling is done by turning the handle or center section in a circular motion. Pressure for drilling is given by bearing down on the head of the bit brace with the heel and palm of the hand. The head on the best bit braces is mounted on ball bearings so that it will turn freely from the rest of the brace. Most braces incorporate a ratchet control that permits the user to make half circles when there is no room for a full circle.
A push drill, similar in appearance to a push-pull screwdriver, operates by a pushpull movement using a spirally headed shaft and chuck to hold the bit. Push drills are best for light jobs. Most have space in the handle for storing extra drill points.
Bits (drill points) have a variety of uses with braces and drills. Each bit and drill is designed for a particular use and should be used for its intended job. Bit diameters are usually marked by a single number—the numerator of a fraction. For example, an auger bit, which is marked by 16ths of an inch, with a number 8 would stand for 8/16" or 1/2". Twist bits are usually marked in the same manner by 64ths of an inch. Thus a No. 8 bit would stand for 8/64" or 1/8".
Countersink bits widen holes so flathead screws may be flush mounted below the surface for a finished appearance.
Expansion bits take the place of many larger bits. They are adjusted by moving the cutting blade in or out by a geared dial or by a lockscrew to vary the size of the hole. They are mounted below the surface for a finished appearance.
Carbide-tipped bits are used for drilling into masonry surfaces. They feature two machined-in spiral threads, one for each cutting edge, to provide passageways for all dust and cuttings from the bottom of the hole. Diameters of carbide tips are the same as the full diameter of the body. A carbidetipped bit can be used in electric drills, drill presses or hand drills for drilling holes in brick, tile, cement, marble and other soft masonry materials.
Twist-drill bits are used in both wood and unhardened metals to make clearance holes for bolts, screws, etc., and to make holes for tapping. Only bits marked HS or HSS are suitable for drilling in metals. Common sizes run from 1/16" to 1/2" diameter by 64ths.
Auger bits are most commonly used with a brace for drilling holes in wood. Their length varies from 7" to 10". Dowel bits are short auger bits from 5" long. Long (ship) auger bits range from 12" to 30".
Spade bits are used in electric drills and drill presses for fast drilling of holes in wood. Electricians use them for drilling clearance holes for wire in floor beams. Bits have a forged, flat paddle with a point and cutting edges on one end and fit a 1/4" drill on the other. Bits are heat treated and cutting angles finish ground. Common sizes run from 3/8" to 1-1/2" in diameter, in 1/16" progression, and are about 6" long.
Power bore bits have a working end similar to auger bits and, like spade bits, are used in conjunction with power drills. Power bore bits produce a smoother hole than spade bits and are used for fine work, such as cabinet making.
Step bits have a graduated design so that variously sized holes can be cut without changing bits. Bits are designed for use with power drills and have self-starting tips eliminating the need for center punching. They can be used on all materials, but are especially designed for use on metals.
Circle cutters cut circular holes in sheets of metal, wood, plastic, hardboard, brass, copper, mild steel, aluminum or composition materials. The cutter features a regular center drill with a cutting tool mounted on an adjustable bar. Diameter of the circle is regulated by a set-screw adjustment on the cutting bar. Downward pressure is applied as the regular bit pulls into the material and forces the cutting tool down in a slowly lowering circle. Ground, hardened cutting tools assure clean, even cutting in a variety of materials. Cutting edges available on hole cutters include high-speed steel bi-metal, carbide grit and diamond grit. Each cutting edge is designed to work best on specific materials. Bi-metal for metal, wood, plastic, etc.; carbide for tile, brick, fibreglass and hard composites; diamond for glass, ceramics and other abrasive materials. Due to the unbalanced load inherent in the design of these tools, for safety’s sake, they must be used only in drill presses or drill stands and never with a handheld drill.
Awls are used to make screw-starting holes when lightly tapped by hand with hammer or soft-face mallet. Awls are also used for scribing along a straight edge to produce a sawing or layout line on wood or soft metal.