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In machining, the rake angle is a parameter used in various cutting processes, describing the angle of the cutting face relative to the workpiece. 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 the 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 the 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 the outer side.
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:
- Increase 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.
