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A saw, when cutting safely, must be sharp. In order to make a cut, a material must be fed into the moving blade. Each moving blade, whether it is a circular saw, band saw or a reciprocating saw, cuts based on this common feature. Another important feature of a saw blade is the geometry of the individual tooth. Whether hollow ground, spring-set, swage or hardened tooth, the geometry of the teeth will dramatically affect the efficiency and performance of a cut.

ANGLES

The geometry of a saw tooth is viewed as several different angles. The measurable angles viewed on the profile side of the saw are called hook angles (positive or negative), clearance angles and sharpness angles. They all are measured using an imaginary line drawn to the center of the arbor hole (center of the saw). For example, the hook angle is measured from the imaginary line from the saw center to the tooth tip and the face of the tooth (gullet side). The hook angle may be either a positive angle or a negative angle. The larger the hook angle (positive), the easier it is for the saw to rip through material. If the tooth cuts more efficiently, the operator will feel less resistance and have less fatigue overall. In general, ripsawing requires larger positive hook angles.

RIP SAWING

Rip sawing may take place with the saw above or below the table. In general, the hook angles will be positive. When ripping lumber with the saw above the lumber, the positive hook angles tend to pull the lumber up. This tendency is counteracted by a series of spring-loaded rollers to securely hold the lumber down onto the feed mat. When the saw is located below the table, the tendency is to pull the lumber safely down to the table while providing minimal resistance to the operator. Generally, ripping saws have fewer teeth, allowing for larger gullets. The common number of teeth on ripping saws are 24 to 30 teeth. Compared to other saws, ripsaws will give minimal resistance to the operator.