Single-Point Cutting:
Let us analyse the forces acting on the chip in orthogonal cutting. These are illustrated in Figure 1(a) and are as follows: Force Fs is the resistance to shear of the metal in making the chip. Fs acts along with the shear plane. Force Fn is normal to the shear plane and it is a backup force on the chip given by the workpiece. Force N acting upon the chip is normal to the cutting face of the tool and it is provided by the tool. Force F is frictional resistance provided by the tool to the chip flow. The latter force acts like downwards against the motion of the chip as it slides upwards along with the tool face.
Figure illustrated the free body diagram of the forces performing on the chip. Forces Fs and Fn are defined by the resultant R, & F & N are replaced from the resultant R'. It means that only two combined forces are acting on the chip, that means R and R'. There are external couples on the chip that curl it, and they might be negated in this approximate analysis. If equilibrium is to present when a body is acted upon by two forces, they might be equal in magnitude, and be collinear. Therefore, R and R' are equal in magnitude, opposite in direction & collinear.