CNC machine contouring motion is controlled using line (G1) and arc (G2/G3) commands. To accommodate this, CAM approximates spline and surface toolpaths by linearizing them –creating many short line segments to approximate the desired shape. How accurately the toolpath matches the desired shape depends largely on the number of lines used. More lines result in a toolpath that closer approximates the nominal shape of the spline or surface, as illustrated in Figure 1.
Figure 1: Tolerances (Toolpath Centerline)