To ensure self-sharpening of the knives, it is important for the upper blade to be inclined by at least: 30'±1° max; in order to be able to eliminate any particles of material which escape during cutting.
Inclinations over these levels can damage the knife, because the knife's material surpasses its yielding load, causing splintering and breakage on the cutting edge.

By increasing the penetration, the material is forcefully pushed by the upper blade to the inside of the sharp blade knife; so, even before starting to cut, the material is pushed and not cut as it will tend to bend, passing between the cutters without being cut at the outlet.