Spindle torque is the rotational force that the machine’s spindle can apply to the cutting tool during operations like milling, turning, and drilling. The spindle torque plays a role in machining performance, especially when cutting hard materials or when removing large amounts of material. Torque is the twisting force applied to an object, causing it to rotate. It’s the force that keeps the spindle rotating under load.
Factors Affecting Spindle Torque
Spindle Speed - Higher spindle speeds generally reduce the available torque since motors have maximum torque at lower RPMs.
Power of the Machine - The machine’s power limits the maximum torque the spindle can deliver.
Material Hardness - Harder materials require higher torque to maintain cutting without tool deflection or breakage.
Cutting Tool Size - Larger tools require more torque to maintain effective cutting force.
Surface Finish - With sufficient torque, the spindle can maintain a consistent cutting action, leading to a smoother finish.
Tool Life - Adequate torque reduces stress on the tool, helping to prevent chipping or breaking.
Spindle Torque Formula |
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\( \tau_s \;=\; \dfrac{ HP_s }{ s }\) (Spindle Torque) \( HP_s \;=\; t_s \cdot s\) \( s \;=\; \dfrac{ HP_s }{ \tau_s }\) |
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| Symbol | English | Metric |
| \( \tau_s \) (Greek symbol tau) = Spindle Torque | \(lbf-in\) | \(N-mm\) |
| \( HP_s \) = Spindle Horsepower (HP) | \(lbf-ft\;/\;sec\) | \(J\;/\;s\) |
| \( s_s \) = Spindle Speed (RPM) | \(rev\;/\;min\) | \(rev\;/\;min\) |
