Top or Back Rake Angle 

The rake angle ground on a tool controls the geometry of chip formation for any given material. It controls the mechanics of the cutting action of the tool. The top or back rake angle of the tool is ground on the top of the tool, and it is a slope formed between the front of the cutting edge and the top face. If the slope is from the front towards the back of the tool, it is known as a positive top rake angle, and if the slope is from the back of the tool towards the front of the cutting edge, it is known as the negative back rake angle. The top rake angle may be ground positive, negative or zero according to the maternal to be machined. When turning soft, ductile materials which form curly chips the positive top rake angle ground will be comparatively more than for turning the hard brittle metals. When turning hard metals with a carbide tool it is the usual practice to give a negative top rake. Negative top rake angle tools have more strength than the positive top rake angle tools.