Stepover
Is stepover the same as stepdown?
No. Stepover is the sideways or radial spacing between passes; stepdown is the axial depth increment into the material.
What range is common for finishing stepover?
Sources commonly describe finishing stepovers as low single-digit to low-teens percentages for high-quality surfaces, especially with ball-nose tools.
Why does stepover affect finish so much?
Because it controls the overlap between adjacent cutter paths, which determines scallop height, visible tool marks, and how much post-processing is needed.
Stepover is the lateral distance a CNC cutting tool shifts between adjacent passes, usually expressed as a percentage of cutter diameter. In CAM, it is effectively the overlap between toolpaths in the XY plane. On the shop floor, it is also called radial depth of cut (RDOC) or cut width, and it directly controls material removal and surface finish.
On the shop floor, stepover is a critical parameter for balancing material removal rate and surface quality. During roughing, a larger stepover (e.g., 40–60% of tool diameter) boosts metal removal and reduces cycle time but leaves more visible scallop patterns and increases cutter load. For finishing, stepover is dropped to the single-digit or low-teens percentage range to minimize scallop height and achieve a smoother finish, especially on curved surfaces and with ball-nose tools. In 3D surfacing, lateral spacing between passes directly dictates surface texture; a low stepover is essential but extends machining time. In CAM, stepover is typically entered as a percentage of tool diameter—for a 10 mm cutter at 20% stepover, each pass shifts 2 mm. On CNC routers, this parameter determines whether a carved panel or moulding requires secondary sanding, as larger stepovers telegraph tool marks through coatings.
Pronounced scallops on finishing passes: The cutter leaves visible ridges, especially on curved surfaces, because passes do not overlap enough to erase the previous tool mark.
Diminishing returns from tiny stepover: Surface quality improves only marginally while cycle time skyrockets, making the job inefficient without functional benefit.
Excessive tool deflection and wear: Aggressive stepover on small cutters or hard materials increases radial load, causing deflection, distortion, and accelerated tool wear.