EngineerBenchConverting lead-screw torque and thrust
A screw converts rotational work into axial movement. Required torque depends on axial force, screw lead, and efficiency. Lead is the axial distance traveled in one revolution; on a multi-start screw it is larger than pitch. Using pitch in place of lead can substantially understate the required torque.
Use an efficiency appropriate to the screw
Efficiency depends on the screw type, friction, lubrication, and operating conditions. The calculation uses the value you enter rather than determining it from thread geometry. Screw RPM and lead give linear travel speed, but motor torque must be available at that speed.
Check compression and unsupported length
The Euler buckling check uses root diameter, unsupported length, elastic modulus, and an effective-length factor. It applies to the represented compression case. Critical speed, bearing support, wear, acceleration, and whether the mechanism can back-drive are separate checks.
Comparing lead, speed, and motor torque
A screw with 5 mm lead advances 5 mm per revolution. At 600 RPM, its ideal linear speed is 3,000 mm/min. With a larger lead, the same RPM produces faster travel, but a given axial force requires more torque at the same efficiency. This tradeoff should be checked against the motor's torque available at operating speed, not only its holding torque.
The load-to-torque relationship estimates steady conversion of rotational work to axial work. Acceleration, seals, guides, and other friction sources can add demand outside that simple balance. When the screw carries compression, unsupported length and end restraint affect buckling strongly. The effective-length factor is a modeling choice about the supports; it is not merely the number of bearings installed. Root diameter, rather than nominal thread diameter, represents the reduced section in the buckling check. A screw may meet torque and buckling requirements yet fail a critical-speed, wear, accuracy, or support-bearing requirement. Keep those checks separate when choosing the complete actuator.
Formula
T = F × lead / (2πη); Euler load = π²EI/(KL)².