Portable Power Drills and Screwdrivers Unit 16 Portable Power Drills and Screwdrivers Portable Power Drills • Power Screwdrivers • Power Drill, Impact Wrench, and Screwdriver Safety

Power drills are available in a variety of sizes and grip configurations and for a variety of power sources. Select the appropriate tool for the operation being performed. Portable power drills are either cordless (battery-operated) or corded (AC-powered) and are available in D-handle or pistol-grip handle designs. See Figure 16-1. Cordless drills receive their power from a removable battery, which is commonly located in the handle. Batteries must be recharged at intervals which depend on the amount and type of usage. Cordless drills can be used for most of the same operations as corded drills. However, cordless drills are most effective for low-torque operations such as drilling thinner wood and driving narrower screws. Corded drills are attached to an AC power source through an electrical cord, which is plugged into an electrical outlet, extension cord, or generator outlet. Corded drills are popular for high-torque operations such as drilling into concrete or drilling large holes in lumber.

Bit shanks are straight or reduced in diameter Bit shanks are straight or reduced in diameter. Reduced-shank bits allow a bit that is larger in diameter than the drill capacity to fit a chuck. The cutting devices that fit into the jaws of a power drill are referred to as bits or drills. The most frequently used bit for drilling small holes is the twist drill. Twist drills may have a straight shank or a reduced shank. See Figure 16-2. Straight-shank bits are available in 1/64″ to 1/2″ diameters. Reduced-shank bits are available in diame-ters up to 1 1/2″. The reduced shank allows a bit that is larger in diameter than the drill capacity to fit a chuck. For example, a 1/2″ diameter bit will fit a 1/4″ diameter chuck if the drill has a 1/4″ diameter reduced shank.

A variety of bits, including twist drills, masonry bits, and hole saws, are commonly used to bore holes in wood and nonwood materials. Various other types of bits are also used for boring into wood, metal, plastics, masonry, and other materials. See Figure 16-3. A feeler bit is used to bore deep holes in wood, and is available in 3/16″ to 3/8″ diameters and 12″, 18″, and 24″ lengths.

A hammer-drill is typically used to drill holes in concrete A hammer-drill is typically used to drill holes in concrete. Carbide-tipped percussion masonry bits are used to drill concrete. Hammer-drills and rotary hammers rotate and drive si-multaneously, causing the bit to spin and hammer at the same time. A hammer-drill is used to drill holes in concrete using masonry bits or twist drills. See Figure 16-4. Hammer-drills should be used when drilling up to 5/8″ holes in concrete. A hammer-drill drills concrete more efficiently than a variable-speed drill because of the rotating and percussive action, which results in faster and cleaner holes. Two factors affect the drilling rate with a hammer-drill—speed and pressure. Speed of bit rotation is affected by the pull of the trigger. The hammering action of a hammer-drill is affected by the pressure applied by an operator. Greater pressure results in better hammering action. The clutches of some hammer-drills can be disengaged so the tool can be used as a conventional drill.

A rotary hammer may be used to chip concrete with a cold chisel bit. A rotary hammer is used to drill holes larger than 5/8″ diameter in concrete or masonry. A heavy-duty rotary hammer drills holes in concrete up to 1 1/8″ diameter with solid drill bits and holes up to 4″ diameter with core drill bits. Rotary hammers operate at a lower rpm than hammer-drills and should not be used to drill wood or metal. Rotary hammers require slotted drive system or slotted drive shank (SDS) chucks and bits. Pressure applied to a rotary hammer does not affect the hammering action; the weight of the tool properly engages the bit. Some models of rotary hammers also accommodate a cold chisel bit for chipping and edging concrete as shown in Figure 16-5.

Impact wrenches are used to install and remove nuts, bolts, and screws. Impact wrenches may be fitted with various size sockets for installing nuts and bolts or a hex adapter for use with hex-shank auger bits or self-feeding bits. See Figure 16-6. Socket sizes range from 1/2″ to 13/16″ in 1/16″ increments. Impact wrenches used for carpentry typically have a 1/2″ or 3/4″ square drive shank. Some impact wrenches may also be fitted with SDS bits.

A drywall screwdriver is specifically designed for fastening gypsum board to support members. A drywall screwdriver, or “screw-shooter,” is specifically designed for fastening gypsum board to wall studs and ceiling joists. See Figure 16-7. A drywall screwdriver is adjustable so a screw head is driven just below the surface of the gypsum board without cutting through the outside layer of paper.