Explain the Back Rake Angle

It measured the downwards slope of the top surface of the tool from the nose to the rear along the longitudinal axis. Its purpose is to guide the direction of chip flow. It also serves to protect the point of the cutting tool. The size of angle depend upon the material to be machined, the softer the material the greater should be positive rake angle. Aluminum requires more back rake angle than cast iron or steel. Back rake angle may be positive neutral or negative. Figure 1 Shows tool with positive back rake angle, figure 2 Show with neutral back rake angle, figure 3 Shows negative back rake angle.

Figure 1: Positive rake angle.

Positive rakes are used when cutting low tensile strength and non ferrous material, material which work harden while being machined. 

    Figure 2: Neutral back rake angle.

Negative rack angle used for machining high tensile strength material, and also for carbide tool cutting material such as grey, cast steels, cast iron, tool steels etc.

  Figure 3: Negative rake angle