Ball Screw Torque Calculator

Driving Torque (Ta): 0.000 Nm
Back-driving Torque (Tb): 0.000 Nm
Total Motor Torque (Required): 0.000 Nm

What is Ball Screw Torque?

Ball screw torque calculation is a critical step in sizing motors for linear motion systems. A ball screw converts rotary motion into linear motion with high precision and efficiency. The amount of torque required to move a specific load depends on the axial force applied, the screw's lead (distance moved per revolution), and the efficiency of the assembly.

The Formula for Driving Torque

The standard formula to calculate the torque required to move a load axially is:

T = (F × L) / (2 π × η)

  • T: Torque (Nm)
  • F: Axial Load (Newtons)
  • L: Screw Lead (meters)
  • η: Efficiency (typically 0.90 for ball screws)

In addition to the driving torque, engineers must also account for friction torque (preload) and acceleration torque to ensure the selected motor has sufficient overhead.

How to Use This Calculator

To use the Ball Screw Torque Calculator, follow these steps:

  • Axial Load: Enter the total force acting against the screw in Newtons. This includes the weight of the load and any external resisting forces.
  • Screw Lead: Input the lead of the screw in millimeters. This is the linear distance the nut travels in one full 360-degree rotation.
  • Efficiency: Enter the decimal efficiency. Most ball screws operate between 85% and 95% efficiency.
  • Friction Torque: If your ball screw is preloaded or has significant seal friction, enter that value here to be added to the total driving torque.

Frequently Asked Questions

Why is ball screw efficiency so high?

Unlike lead screws (acme screws) that rely on sliding friction, ball screws use recirculating ball bearings to create rolling friction. Rolling friction is significantly lower than sliding friction, allowing ball screws to reach efficiencies over 90%.

What is back-driving torque?

Back-driving torque is the torque generated at the screw shaft when an axial load is applied to the nut. Because of their high efficiency, ball screws can easily back-drive, meaning they may require a brake or holding torque to prevent the load from falling when power is removed.

Does lead affect torque?

Yes. A larger lead (e.g., 20mm vs 5mm) requires more torque to move the same axial load, but results in faster linear travel speeds for the same RPM.