Choosing Stepover for 3D Milling

In 3D milling with ball-nose tools, stepover directly controls surface texture and cycle time. Smaller stepovers improve finish but increase machining time.

Stepover, tool radius and scallop height

When finishing with a ball-nose endmill, each pass leaves a small cusp or "scallop" between adjacent toolpaths. A simple geometric approximation is:

h ≈ s² / (8 × R)
    

where h is scallop height, s is stepover and R is tool radius. You can explore this relation with the Scallop Height Calculator.

Working backwards: stepover from target scallop height

If you know the maximum scallop height you can accept, you can estimate a suitable stepover with:

s ≈ √(8 × R × h)
    

Use the Stepover From Scallop Height Calculator to quickly try different tool radii and target surface qualities.

Practical guidelines

• Roughing: larger stepovers, scallop height is less critical
• Semi-finishing: use a stepover that leaves a consistent stock for finishing
• Finishing: stepover is often driven by required Ra/Rz or polishing strategy

In practice, the "best" stepover is a compromise between required surface quality, allowed polishing time and available machine hours. Use the geometric formulas as a starting point, then tune based on real parts, materials and customer expectations.