In brief
A ball screw converts rotary motion into precise linear motion with low friction by means of recirculating balls between the screw shaft and nut.
Contents
What is Ball screw?
A ball screw consists of a threaded screw shaft, a nut and balls that roll in the thread grooves and recirculate via a return system in the nut. Compared with a trapezoidal lead screw with sliding friction, efficiency is considerably higher, wear is lower and positioning accuracy is better. Ball screws are not self-locking; on vertical axes, a brake on the drive is therefore usually required.
Key ratings are nominal diameter, lead, length, accuracy class, load ratings and preload. Rolled screws are economical, while ground screws achieve higher accuracy. The nut is available as a single nut, preloaded single nut or double nut; preload eliminates axial play. Tolerance classes and terms are described in the ISO 3408 series of standards. The system includes the fixed and floating bearing supports of the screw and the coupling to the motor.
Ball screws drive the axes of machine tools, presses, handling equipment and electromechanical cylinders. Wear shows up as increasing backlash, noise or positioning deviations; causes include contamination, insufficient lubrication, collisions and misalignment.
In practice: maintenance and procurement
For a replacement, nominal diameter, lead, total length, end machining according to drawing, nut type, preload and accuracy class are needed. It is often worth checking whether a repair by regrinding and fitting new balls is possible instead of manufacturing a completely new screw.
Synonyms and abbreviations: ball screw drive · ball screw spindle · recirculating ball screw · ball screw assembly
Frequently asked questions
What is the difference between a ball screw and a trapezoidal lead screw?
The trapezoidal lead screw works with sliding friction between thread and nut, has lower efficiency and, depending on the lead, is self-locking. The ball screw uses rolling friction, achieves high efficiency, low heat generation and high accuracy, but is not self-locking and is more expensive. Trapezoidal screws are suitable for simple adjustments, ball screws for dynamic and precise axes.
What does the lead of a ball screw mean?
The lead indicates how far the nut moves axially for one revolution of the screw, for example 5 or 10 millimetres. Small leads offer high resolution and force, large leads high traverse speed. When replacing, the lead must match exactly, otherwise the position measurement and controller parameters will no longer be correct.
What information is needed to replace a ball screw?
Nominal diameter, lead, thread direction, total length and thread length, machining of the screw ends, nut type with flange dimensions, preload and accuracy class are required. The safest basis is a drawing or the machine manufacturer’s part number. Photos of the nut and screw ends help with identification.
Can a ball screw be repaired?
Often, yes. Specialist workshops inspect the screw and nut, regrind worn raceways, fit new oversize balls and reset the preload. Whether this is worthwhile depends on the wear pattern, the accuracy requirement and a comparison with the price and lead time of a new part.