Rake angle

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

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, negative, and neutral.

POSITIVE RAKE:-A tool has a positive rake when the face of the cutting tool slopes away from 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.

Generally, positive rake angles:

• 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, by contrast:

• Make the tool more blunt, increasing the strength of the cutting edge.
• Increase the cutting forces.
• Can increase friction, resulting in higher temperatures.
• Can improve surface finish.

A zero rake angle is the easiest to manufacture, but has a larger crater wear when compared to positive rake angle as the chip slides over the rake face.^[1]

Recommended rake angles can vary depending on the material being cut, tool material, depth of cut, cutting speed, machine, and setup. This table summarizes recommended rake angles for single-point turning on a lathe; rake angles for drilling, milling, or sawing are often different.

References