Training Program - The high-speed cutter

Knife angle

Two forces are acting upon the knife:

Vertical force: A large knife angle can bear a higher resistance of the material than an acute one. This plays an important role when dealing with overcuts.
Lateral force: Especially when dealing with fluffy voluminous material the force acting upon the blade is lower with an acute knife angle. This can be noticed on the undercut.

The following rule applies:

Hard material to be cut – large knife angle
Soft material to be cut – acute knife angle

Commercially available knives have angles from 17 to 28°. Some cutting machine producers recommend 19 degrees for book printing paper and 24 degrees for art paper, for example. For paper processing an average knife angle of 22 degrees is sometimes recommended, when you work with different types of paper. Polar-Mohr generally recommends a knife angle of 24 degrees.

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Fig. 10: Knife with double bevel

Another way to adjust to hardness variations of the material being cut is the double bevel. It is obtained by grinding a second knife angle at the tip of the blade. In this way the tip is enabled to cushion the resistance of hard material being cut. On soft materials being cut the fluffy material exerts a lower pressure on the sharp total angle of the knife.