Positive Rake Angle vs Negative Rake Angle: Difference and Comparison

Key Takeaways

1. Positive rake angles have the cutting edge set higher than the major cutting edge, leading to sharper cutting. Negative rake angles have the cutting edge lower, leading to more blunt cutting.
2. Positive rakes produce lower cutting forces and temperatures. They are ideal for machining soft or ductile materials. Negative rakes generate higher forces and temps better for hard/brittle materials.
3. Positive rakes exert an upward curling force that improves chip control and breaking. Negative rakes exert a downward force causing chips to adhere to the tool.

What is Positive Rake Angle?

A positive rake angle is a cutting edge above the positive angle (reference plane). The cutting action of a positive rake angle is most suitable for bringing forth smooth finishes and cutting soft materials. In a positive rake angle, the tool life is shorter because of the continuous wear on the cutting edge.

A positive rake angle is best for high-speed machining of soft materials such as – aluminium. The cutting force of the positive rake angle is relatively low, which helps reduce power consumption. The surface finish in positive rake angle is relatively smooth.

What is Negative Rake Angle?

A negative rake angle is a cutting edge below the negative angle (reference plane). The cutting force of the negative rake angle is high, leading to more power consumption. The cutting action of a negative rake angle is efficient for cutting hard and tough materials.

In a negative rake angle, the temperature produced is high. Also, the temperature produced is high. The surface finish for the negative rake angle could be smoother.

Difference Between Positive Rake Angle and Negative Rake Angle

1. The definition of positive rake angle is the cutting edge present above the positive angle (reference plane). On the other hand, the definition of a negative rake angle is the cutting edge below the negative angle (reference plane).
2. The cutting action of a positive rake angle is most suitable for bringing forth smooth finishes and cutting soft materials. In contrast, on the other hand, the cutting action of a negative rake angle is efficient for cutting hard and tough materials. 
3. The cutting force of the positive rake angle is relatively low, which helps reduce power consumption. On the contrary, on the other side, the cutting force of the negative rake angle is high, leading to more power consumption. 
4. In a positive rake angle, the tool life is shorter because of the continuous wear on the cutting edge. In comparison, on the other hand, in a negative rake angle, the tool life is more prominent, and there is less possibility of wear.
5. In a positive rake angle, the exhibiting temperature is low, whereas, on the other hand, in a negative rake angle, the temperature produced is high.
6. A positive rake angle can form continuous chips (longer chips). While on the other hand, a negative rake angle can form segmented or discontinuous chips (shorter chips).
7. The surface finish in positive rake angle is relatively smooth. On the contradictory side, the surface finish for the negative rake angle could be smoother. 
8. The cutting stability in the positive rake angle is less because of the reduced strength due to interrupted cutting. At the same time, the cutting stability in the negative rake angle is more because of the improved strength occurring due to interrupted cutting. 
9. A positive rake angle is best for high-speed machining of soft materials such as – aluminium. Comparatively, on the other hand, the negative rake angle is best for machining tough materials such as – hardened steel and stainless steel.

Comparison Between Positive Rake Angle and Negative Rake Angle

Parameter of Comparison	Positive Rake Angle	Negative Rake Angle
Definition	The cutting edge is present above the positive angle (reference plane)	The cutting edge is present below the negative angle (reference plane)
Cutting Action	They are suitable for bringing forth smooth finishes and cutting the soft materials	They are efficient for cutting hard and tough materials
Cutting Force	Low	Higher
Tool Life	Shorter	Longer
Cutting Temperature	It generates low-cutting temperature	It generates high-cutting temperature
Chip Formation	They are able to form continuous chips (longer chips)	They are able to form segmented or discontinuous chips (shorter chips)
Surface Finish	Smooth finish	Moderate smooth finish
Cutting Stability	It is less stable in nature	It is more stable in nature
Application	Best for high-speed machining of soft materials such as – aluminium	Best for machining tough materials such as – hardened steel and stainless steel

References

1. https://www.sciencedirect.com/science/article/abs/pii/S0890695504000197
2. https://www.sciencedirect.com/science/article/abs/pii/S0043164804003333