Rake angle

Rake angle is a parameter used in various cutting and machining processes, describing the angle of the cutting face relative to the work. There are three types of rake angles: positive, zero or neutral, and negative.

• Positive rake: A tool has a positive rake when the face of the cutting tool slopes away from the cutting edge at inner side.
• Zero rake: A tool has a zero (or neutral) rake when the face of the cutting tool is perpendicular to the cutting edge at inner side.
• Negative rake: A tool has a negative rake angle when the face of the cutting tool slopes away from the cutting edge at outer side.

A schematic showing positive (left) and negative (right) rake angles.

Positive rake angles generally:

• Make the tool more sharp and pointed. This reduces the strength of the tool, as the small included angle in the tip may cause it to chip away.
• Reduce cutting forces and power requirements.
• Helps in the formation of continuous chips in ductile materials.
• Can help avoid the formation of a built-up edge.

Negative rake angles generally:

• Increasing the strength of the cutting edge. The tool is more blunt.
• Increases the cutting force.
• Increases the power required for a cut.
• Can increase friction, resulting in higher temperatures.
• Can improve surface finish.

Zero rake angles:

• Easier to manufacture.
• Easier to resharpen.
• Less power and cutting forces than a negative raked tool.
• Chip will wear and 'crater' the rake face.[1]