Ball Nose Stepover Calculator

Inputs

Solve for

Choose whether you know the stepover (and want the scallop height) or the target scallop (and want the stepover that produces it).

Tool diameter (D)

Diameter of the ball-nose end mill. The ball radius is r = D/2.

Stepover (s)

Sideways distance between parallel passes (the radial step). Smaller stepover → smaller scallop.

Default result

Scallop height(h)

0.01043mm

Peak-to-valley cusp left between passes.

Also computed

Stepover(s)0.5mm

The radial step used / required.

Method notes 4 notes

Ideal geometry: with ball radius r = D/2 = 3 (mm internal), the scallop is h = r − √(r² − (s/2)²); inverted, s = 2·√(r² − (r − h)²).
Halving the stepover roughly quarters the scallop height — the cusp grows with the square of the stepover.
This is the theoretical finish on a flat, horizontal surface. On a slope the effective cusp is larger; tool deflection, runout and wear all add to it.
Geometry only: it assumes a true ball nose and ignores the cutting-edge condition, deflection and the surface slope. Treat the result as a best-case starting point.