2.7.3 Hole Saws High-speed hole saws are designed for cutting steel, aluminum, copper, brass, sheet metal, stain- less steel, wood, or plastics. See Figure 2-36. The high-speed cutting edges are welded to steel bodies to produce clean, accurate holes. Shatter- resistant construction makes them safe and durable. Hole saw sets, Figure 2-37, are available and include sizes ranging from 9⁄16″ (14 mm) to as much as 5″ (127 mm). Individual hole saws are quickly attached to an arbor (spindle or axle) that has a twist drill for starting the pilot hole. drilled. Twist drills can be purchased separately or in sets, with drill sizes ranging from 1⁄16″ to ½″. See Figure 2-34. 2.7.2 Wood Bits The spade-type wood bit is designed to cut straight or angled holes in wood, plastic laminate, plaster, foam insulation, and similar materials. Like twist drills, they are available as individual bits or in sets, in sizes ranging from ¼″ to 1½″ (6 mm to 38 mm). As shown in Figure 2-35, sizes are stamped on each bit. Spade-type bits can be resharpened with a file or grinder. Extension bars are available for extended reach. Auger-type wood bits are generally used for drilling large holes and are available in sizes up to 2½″ (63.5 mm). The pilot screw tip draws the bit into the wood. Cutting blades can be sharpened with a file. Lips Flutes Point Body Shank Goodheart-Willcox Publisher Figure 2-33. Parts of a typical twist drill bit. Goodheart-Willcox Publisher Figure 2-34. Twist drill bits are available individually or in sets. Most often, a technician starts with a set, then replaces bits individually as necessary. Goodheart-Willcox Publisher Figure 2-35. Spade-type bits are used to bore medium to large holes in wood and similar nonmetal materials. Sizes are stamped on each bit. Twist drill Hole saw teeth Malco Products, Inc. Figure 2-36. Hole saws are attached to an arbor that includes a twist drill for boring a pilot hole. Chapter 2 Hand Tools 29 Copyright Goodheart-Willcox Co., Inc.