Small (sometimes called “mini”) hacksaws, Figure 2-32, are used for working in very confined areas or for flush-cutting. These small hacksaws are indispensable to the technician. 2.7 Drill Bits Various types of drill bits are used for cutting holes. Each is designed for use on a specific type of material: drill bits designed for wood cannot be used on metal or concrete bits for metal can be used on wood, but not concrete bits for concrete cannot be used on metal or wood. 2.7.1 Twist Drill Bits Twist drill bits are used to cut small-diameter holes in metal or wood. Bits made of high-speed steel are most common and are sometimes carbide-tipped. A twist drill bit has three prin- cipal parts: a shank that is clamped into the drill chuck, a body with two spiral grooves called flutes, and a cone-shaped cutting end called the point. See Figure 2-33. The flutes act as channels for the escape of metal chips from the hole being • Always wear safety goggles when using a hammer to drive nails or strike objects. • Never strike one hammer with another hammer. • Never use a hammer that has a loose or damaged handle. • Never use the side or “cheek” of a hammer for striking any object, except in the case of the setting hammer. • Never grind or redress the face of a hammer. If the hammer head is damaged, discard and replace it. 2.5.7 Repair or Replace? Discard hammers that have damaged heads they are dangerous to use. Damage is indicated by dents, chips, excessive wear, or a broken claw. Damaged wood or fiberglass handles can usually be replaced. 2.6 Hacksaws Hacksaws are used to cut all types of metal objects, Figure 2-31. Hacksaw blades are selected according to the number of teeth per inch: 18 (coarse), 24 (medium), and 32 (fine). The blade should be fastened tightly in the frame, with the blade teeth pointed away from the handle. At least two teeth should contact the metal being cut, or the saw will catch and bind. You can use one or two hands on the saw to make cuts. Press down lightly on the forward stroke and release pressure on the backstroke. Avoid rapid strokes, else the blade will overheat and become dull. Use 50 to 60 strokes per minute. Goodheart-Willcox Publisher Figure 2-31. The hacksaw is an important tool for cutting metal. Blade teeth should face away from the handle so the saw cuts on the forward stroke. B A Vermont American Figure 2-32. For flush-cutting metal or working in close quarters, the mini-hacksaw is the ideal tool. A—A frame- type mini-hacksaw. B—A model with a contour grip. 28 Heating and Cooling Essentials Copyright Goodheart-Willcox Co., Inc.