Cutting power is the force required for the tool to machine a workpiece, in other words the resistance from the workpiece. This resistance is called cutting resistance, and is divided into three forces as shown in the image to the right.
Principal force
Force generated in the opposite direction to the rotation of the cutter. Determines the power required to rotate the main spindle. Affects heat generation.
Back force
Force acting towards the spindle. Causes the workpiece and tool to flex. Therefore, a larger back force has negative influence on dimensional accuracy.
Feed force
Force that is generated in the opposite direction to the feed. As the feed force increases it tends to bend the main spindle and if the feed force is too high the surface finish can deteriorate.