Thread Whirling Head Tilt & Feed Calculator

Principles of CNC Thread Whirling for Precision Components

Thread whirling is an eccentric high-speed cutting process used on Swiss-type automatic lathes to manufacture high-precision, high-aspect-ratio threads in a single pass. Primarily used for medical bone screws, dental implants, miniature leadscrews, and worm gears, whirling eliminates thread deflection by supporting the raw stock directly inside the guide bushing right up to the cutting zone.

Kinematics & Helix Tilt Angle Calculation

The whirling ring contains multiple radially mounted indexable carbide inserts (typically 6 to 12) rotating about an eccentric axis. To prevent the trailing edge of the cutting inserts from gouging or dragging against the thread flank, the entire live whirling spindle must be physically tilted to match the thread's helix lead angle $\beta$:

Workpiece Peripheral Speed and Axial Feed

Unlike conventional single-point threading where the workpiece rotates at high speed over multiple passes, thread whirling finishes the complete thread profile in one single pass. The cutter spindle spins at high velocity ($n_c$), while the workpiece spindle rotates slowly ($n_w$):

• Cutter RPM ($n_c$): $n_c = \frac{1000 \cdot V_c}{\pi \cdot D_c}$
• Workpiece Peripheral Feed Speed ($v_{fw}$): $v_{fw} = f_z \cdot z \cdot n_c \cdot \frac{1}{\cos \beta}$ (mm/min along the thread helix).
• Workpiece RPM ($n_w$): $n_w = \frac{v_{fw}}{\pi \cdot d_p}$
• Z-Axis Axial Feed ($F_z$): $F_z = n_w \cdot \text{Lead}$ (mm/min).