The term positive and negative rake inserts refers to the angle between the cutting edge relative to the machined surface.
The illustrations show an insert with flat top. If the cutting edge is equipped wiht a chip braker, positive cutting can be obtained even though the tool's angle is negative.
1. Negative rake inserts
Angled according to the first picture. These inserts can handle higher cutting forces permitting higher removal rates, it also places higher demands on the machine and the tool holder stability to avoid vibrations.
The chips are also more brittle, which means that you rarely need to use a chip breaker.
These inserts are usually double sided resulting in cutting edges on both sides of the insert.
2. Neutral rake inserts
3. Positive rake inserts
Angled according to the second picture. These inserts result in lower cutting forces, which reduces the risk of vibration and gives a better surface smoothness. The low force enables the machining slender parts.