How is ball screw torque calculated?

T = F*lead/(2*pi*eta), eta about 0.90 for ball screws.

What efficiency for ball screws?

0.85-0.95, typically 0.90. ACME lead screws: 0.25-0.50.

How to avoid critical speed?

Operate below 80% of Ncrit. Use larger dia, shorter length, better end fixity.

L10 = (Ca/F)^3 x 10^6 rev. Load cubed inverse relationship.

Fixed-fixed: 4.73. Fixed-supported: 3.93. Supported-supported: 3.14.

Free Engineering Tool #077

Ball Screw Calculator — ISO 3408

ISO 3408 ball screw design. Enter lead, nominal diameter, axial load, and speed to calculate drive torque, efficiency, critical speed, and rated life.

ISO 3408Critical SpeedLife L10

Results

Drive Torque

—

Efficiency

—

Critical Speed

—

Rated Life L10

—

Linear Speed

—

Drive Torque

Critical Speed

Life

Apply 0.8 safety factor to critical speed. Use fixed-fixed supports where possible.

Ball Screw Calculator ISO 3408 | Free Tool #077

Published by admin on February 15, 2026 February 15, 2026

Results

Drive Torque

Critical Speed

Life