Positive Rake

Positive rake referes to a rake angle greater than 90 degrees.  Rake is the angle from the workpiece wall to the cutting tool at the cutting edge. The back rake angle affects the ability of the tool to shear the work material and form the chip.  Positive rake angles reduce the cutting forces resulting in smaller deflections of the workpiece, tool holder, and machine. If the back rake angle is too large, the strength of the tool is reduced as well as its capacity to conduct heat. In machining hard work materials, the back rake angle must be small, even negative for carbide and diamond tools. The higher the hardness, the smaller the back rake angle. For high-speed steels, back rake angle is normally chosen in the positive range.