Influence of Various Angles on Tool Design

Back Rake Angle

The rake angle of any single point cutting tool is useful in estimating the direction of chip flow across the face of the tool.

1. A positive back rake angle is responsible to move the chip away through the machined workpiece surface.

2. The tool penetrates the workpiece simply and tends to shear the material off rather than compressing. Thus the cutting efficiency is best with positive back rake angle.

3. Forces and power consumption decrease with increase in positive back rake angle.

4. If positive back rake angle raise, resisting area of tool decreases.

 In general, for softer workpiece, back rake angle of 25° to 30° is preferable and for harder workpiece back rake angle of 7° to 10° is preferable. Negative back rake angle is preferable for carbide tool. Carbide tools are extremely brittle in nature, so deformation takes place if we provide positive back rake angle. To ignore deformation, negative back rake angle is provided. Positive back rake angle is utilized for machining low tensile strength and non ferrous materials. They are also utilized during machining of long/small diameter shafts or material that is work hardened during machining. Negative back rake angles are utilized for machining high tensile strength material, interrupted cuts and heavy feed.