Introduction:
In the field of machining, cutting tools play a crucial role in shaping and forming the workpiece. The design and geometry of cutting tools significantly impact the cutting process. One of the important factors to consider in cutting tool design is the rake angle. The rake angle refers to the angle between the cutting edge of the tool and a perpendicular line to the workpiece surface.

Explanation:
1. Definition of positive rake angle:
- Positive rake angle is when the cutting edge is inclined in the direction of tool movement.
- It is measured in degrees and can be designated as a positive value.

2. Purpose of large positive rake angle in cutting tools:
The main reason for providing cutting tools with a large positive rake angle is to reduce the magnitude of cutting forces. This is achieved through the following mechanisms:

2.1. Reduced friction and rubbing:
- A large positive rake angle helps in reducing friction and rubbing between the tool and the workpiece.
- When the rake angle is positive, the cutting edge is presented to the workpiece at an inclined angle.
- This results in a slicing or shearing action rather than a rubbing or scraping action.
- As a result, the cutting forces are reduced, leading to improved machining efficiency and reduced tool wear.

2.2. Improved chip formation:
- The large positive rake angle promotes the formation of thin, continuous chips during the cutting process.
- The inclined cutting edge allows the chip to flow smoothly and evacuate from the cutting zone.
- This prevents the chip from interfering with the cutting action and reduces the chances of chip jamming or workpiece damage.

2.3. Better heat dissipation:
- Another advantage of a large positive rake angle is improved heat dissipation.
- The inclined cutting edge allows for better chip flow and chip evacuation, which helps in removing heat generated during the cutting process.
- This reduces the chances of heat buildup at the cutting edge, which can cause tool failure or workpiece damage.

Conclusion:
In summary, cutting tools are provided with a large positive rake angle mainly to reduce the magnitude of cutting forces. This is achieved by reducing friction and rubbing, promoting improved chip formation, and enhancing heat dissipation. The use of a large positive rake angle improves machining efficiency, reduces tool wear, and ensures better surface finish on the workpiece.