Saw is a cutting tool that has a thin blade notched with pointed teeth. Material is cut with a saw by moving the blade across it in a slicing motion. Saws are manufactured for use in cutting wood, metal, plastics, fabrics, meat, concrete, or any material that is softer than the saw blade.
Sawteeth are bent slightly out of the plane of the blade, alternately to the left and to the right. The extent of bending is called the set of the teeth. The set determines the width of the kerf, or cut, made in the sawed material. Each sawtooth has two edges: the cutting edge, called the face, and the back edge. The angle of the tooth is the angle between the face and the back edge with the point as the vertex.
A wide variety of saws are made for different purposes. The saw blades vary in width and thickness and in the number of teeth per inch they contain. They usually are categorized as hand saws, stationary and portable power saws, and industrial power saws. Hand saws and power saws are used by craftsmen and laymen. Industrial saws are normally used in the logging, manufacturing, and construction industries.
Major Types of Saws
Hand Saws. Hand saws used for cutting wood include rip, crosscut, back, dovetail, compass, keyhole, coping, turning, pruning, veneer, flooring, miter-box, and docking saws. Hand saws used for cutting metal include the metal-cutting hand saw and the hacksaw. Meat and frozen foods are cut with a butcher's saw or a kitchen saw.
The most common handsaws are the ripsaw and the crosscut saw, which are carpenter's saws used for cutting wood. The ripsaw is used for cutting wood with the grain, and the crosscut saw, which has more points per inch than the ripsaw, for cutting across the grain. Less common and more specialized saws include the hacksaw, which has a very thin blade reinforced with a metal strip along its back, and is used for miter-box or dovetail cutting; the keyhole saw, which has a blade tapered to a point for use in curved cutting; the coping saw, which has a very narrow, fine-toothed blade held in a metal frame and is used for shaping; and the hacksaw, also held in a frame, which is used primarily for cutting metal.
Power Saws. Most power saws are powered by electricity. They may be portable or also installed as part of a bench or table fixture. The most common power saw is the circular saw. Its blade is a disc, with teeth around the periphery, that is mounted on a spindle and rotated at a high speed. Other important power saws are the band saw, which has a narrow cutting band mounted on two pulleys, and the scroll saw, which has a short reciprocating blade.
Stationary power saws include the table saw, the overarm (radial) saw, the band saw, and the jigsaw. Portable power saws include hand electric power saws, which have a circular blade, saber and bayonet saws, which have a narrow reciprocating blade; and chain saws, which have teeth anchored to a chain belt.
In power saws, only the blade needs to be changed to obtain the required variety of cutting. There are various kinds of blades, including crosscut, rip, combination, plywood, planer, concave, metal-cutting, and masonry blades.
How to distinguish a ripsaw from a crosscut. From a distance both saws resemble the one pictured at the left. However, their teeth differ. The crosscut saw is designed to cut across the grain of the wood and the ripsaw, to cut with the grain. The crosscut saw has beveled teeth shaped to cut like knives through wood fibers. There are from 7 to 12 points, or teeth, per inch (2.8-4.8 points per cm). Ripsaw teeth, shaped to cut like chisels, are unbeveled. They are larger and have a slightly wider set than crosscut teeth.
Glossary of Saw Terms
Angle of Cut
The angle between the blade and the material being cut; it is 45° for crosscut saws and 60° for ripsaws.
Pinching of the blade due to inadequate set.
The curved cutting edge of a hand saw.
The angle contained within a tooth.
The rear end of a hand saw.
Trimming the cutting edge of a blade to ensure uniform tooth length.
The width of a cut made by saw teeth.
A sharp bend in a blade, making it useless.
The angle at the back edge of a tooth to allow entry clearance into the material.
Points per Inch
The number of tooth points per inch of blade.
The face angle of a tooth as it enters material.
The alternate bending of teeth to allow cutting clearance.
The curved back edge of a handsaw to achieve lightness.
The front end of a hand saw.
Selection of Saws
The selection of a hand saw depends on the type of work to be done. A 26-inch (64-cm) crosscut usually has 8 tooth points per inch and is used for rough-sawing boards to length. A 20- to 24-inch (51-61 cm) crosscut usually has 10 to 12 points per inch and is used for fine cuts. Hacksaws, dovetail saws, and miter-box saws, which are primarily used for making joints, have 12 to 15 points per inch. Keyhole, compass, and coping saws are used for cutting irregular shapes. The less common ripsaw cuts parallel to the wood fiber. It is 26 inches long and most commonly has 5.5 points per inch.
Metal-cutting hand saws are available in the conventional hand-saw shape with 15 tooth points per inch or as a hacksaw, which has a 14- or 32-point blade held rigidly in a metal frame. Butcher saws are similar to hack saws but have longer blades. They contain about 11 tooth points per inch.
Power table saws usually have % to 3 h.p. motors and have circular blades 6 to 14 inches (15-36 cm) in diameter. The shaft speed should be 3,450 rpm. These saws are capable of cutting material to width and length, as well as cutting rabbet, dado, plow, miter, and tenon joints.
Band-saw blades have teeth shaped on narrow bands of metal tensioned between two pulley wheels, with the cutting action toward the table. Blades are specialized for cutting wood, metal, plastic, fabric, or foodstuffs in straight or irregular shapes.
Power jigsaw blades, which reciprocate vertically by means of a pulsating lower shaft and a spring-loaded upper shaft, are used for cutting irregular shapes.
Radial-arm saw blades are attached directly to the shaft of the motor, which is suspended over a table via a yoke and overarm to a rear column. Blade sizes range in diameter from 8 to 20 inches (20-50 cm), and industrial saw blades are as large as 44 inches (118 cm) in diameter. They are mainly used as cutoff saws but can be used for cuts similar to those of a table saw.
Power hand saws are patterned from the stationary machines, with sizes being designated by blade diameter or length.
Care of Saws
Hand saws and power-saw blades must be kept clean for efficient use. Wet or dry abrasive paper along with varsol or kerosene as a lubricant will polish the metal sufficiently. Any rubbing should be done parallel to the manufacturer's machining.
Usually, the teeth of saws are set alternately to allow cutting clearance. Hand saws can be set with a hand-operated saw set. Circular saw blades can be set with a punch and anvil or by a machine. Blades can be sharpened by hand filing or by special grinding wheels, but such tasks should be done by an experienced person.