Scallop Height Calculator: Ball Nose Stepover

Published September 22, 2026 · MfgWorkbench editorial reference

Compare finishing stepovers for a spherical ball-nose cutter moving across a flat surface. Choose whether the known value is stepover or target scallop height.

The flat-surface ball-nose model

For ball radius R and parallel-path stepover s, h = R − √(R² − (s/2)²). Solving for stepover gives s = 2√(2Rh − h²). All inputs and the principal output are in millimeters; height is also shown in micrometers.

The cutter is modeled as an ideal sphere tangent to a flat plane, with neighboring passes in the same plane. The allowable stepover is no greater than the ball diameter. The inverse calculation accepts a height no larger than the radius. These bounds describe the geometry, not a recommended finishing window.

Example: 6 mm ball end mill

With a 6 mm ball diameter and 0.5 mm stepover, the calculated height is 0.0104348 mm, or 10.4348 µm. For a target of 0.005 mm, the inverse calculation gives approximately 0.346266 mm stepover. A tighter height requirement creates more toolpath passes and generally more machining time.

For small stepovers, h ≈ s²/(8R). Halving stepover therefore reduces ideal cusp height to roughly one quarter. The tool uses the exact square-root expression rather than that approximation.

Do not confuse cusp height with Ra

This output is a geometric peak left between paths. Actual roughness also includes feed marks, vibration, runout and material effects. A curved workpiece changes the effective contact geometry; a tilted tool or a barrel tool cannot be represented merely by entering its nominal diameter.

Use CAM scallop control and verify the contact model for freeform finishing. Inspect the resulting surface, including areas where slope changes or the cutter passes close to its tip. The calculator helps choose a comparison value for testing, not certify a finish specification.