Before going into the forces of tool cutting, it is important to briefly discuss the difference between orthogonal and oblique cutting. Orthogonal cutting occurs when the knife edge is perpendicular to the direction of travel. Oblique cutting occurs when the knife edge is not perpendicular (i.e. at an angle) to the direction of travel. (3)
In pure orthogonal cutting, there is a force normal to the cutting plane, force parallel to cutting plane, and the resulting force [see figure(c) above]. In oblique cutting there are also lateral forces determined by the shear angle (λ) [see figure(d) above]. We will talk more about shear angles in the next section. Also, if the tool is moving sideways or vibrating during the cut, there will be lateral forces as well [see figure(e) above]. (3)