3D Contour Finishing Strategy

Theoretical Background of Z-Level (Contour) Milling

The 3D Contour strategy (traditionally referred to as Constant Z or Z-Level Finishing in the CNC programming industry) is one of the most reliable and fundamental finishing operations in 3-axis computer-aided manufacturing (CAM). The core logic of the algorithm relies on slicing the 3D CAD model horizontally at fixed vertical coordinates (Z-heights). The toolpath generator calculates the intersection between these horizontal planes and the part's surface geometry, producing a series of closed or open horizontal loops (contours) at descending depths.

                  [Tool Axis / Z-Axis]
                           |
                           v
              ___________     ___________  <- Z-Level 1 (dz)
             /           \   /           \
            /             \_/             \ <- Z-Level 2 (dz)
           /                               \
          /                                 \ <- Z-Level 3 (dz)
         /                                   \
        /                                     \ <- Z-Level 4 (dz)

Steep vs. Shallow Slopes

The effectiveness of a Constant Z toolpath is highly directional. Its performance is directly tied to the surface slope angle ($\alpha$) relative to the XY horizontal plane: