Ball end mill speeds and feeds (effective diameter, RPM, scallop height)
At shallow depths a ball end mill cuts on a diameter smaller than the tool diameter (effective diameter). This calculates RPM from the effective diameter and the scallop (cusp) height from the stepover.
◠Ball end mill calculator
Effective diameter De—mm
Spindle speed n—rpm
Feed rate Vf—mm/min
Scallop height h—µm
Surface speed at full D (reference)—m/min
De = 2 × √(ap × (D − ap)) (if ap ≥ D/2, De = D) n = 1000 × Vc ÷ (π × De) Vf = fz × z × n h = R − √(R² − (Pf/2)²) (R = D/2)
Notes
- When a flat surface is cut without tilting the tool, the surface speed at the tip center is zero. Tilting the tool or the workpiece moves the cut away from the center and gives a steadier finish (one reason for tilting the tool on 5-axis machines).
All values are guides. Start from the tool maker’s recommended cutting data and adjust for your machine, workholding and coolant. Calculations run in your browser; nothing you enter is sent anywhere.