Forces in Orthogonal Cutting

A dynamometer capable of measuring forces in 3 directions (only 2 are needed in orthogonal cutting) can be used to measure cutting forces. In the diagram below the reactions to these forces, which are acting on the tool, are shown:

F_c acting in the direction of cutting

F_t thrust force needed to keep the tool in the workpiece (direction perpendicular to the workpiece surface). At high positive rake angles the thrust force is negative and the tool is pulled into the workpiece.

The resultant force on the tool, P_r, is made up of a normal force, P_n acting perpendicular to the tool face and F the friction force acting along the face.

Knowledge of the shear angle, phi, will allow the deformed chip thickness to be estimated.