Stretching

Stretching refers to the deliberate axial preloading of a ball screw or trapezoidal screw by mechanically stretching the spindle shaft. It creates a permanent tensile stress in the spindle and complements the preload of the nut.

Purpose

• Compensation for thermal expansion: When the spindle heats up during operation, it expands. Thanks to the pre-applied tensile stress, a small residual tensile force remains even at the maximum expected operating temperature, preventing harmful compressive forces or buckling of the spindle.
• Enables a fixed-fixed bearing arrangement on both sides instead of a fixed-loose arrangement, thereby increasing the spindle’s axial stiffness and critical speed.

Technical Implementation

The required calculation is derived mathematically from

$Temperature change × coefficient of thermal expansion × spindle length$.

This is achieved through a fixed bearing arrangement on both sides with axial force transmission via bearing clamping elements, supplemented in some cases by negative pitch compensation to prevent undesirable pitch deviations. The frictional forces that arise in this process require a correspondingly careful bearing design.

Practical relevance

Stretching is primarily used in machine tools and precision drives, where thermal stability and positioning accuracy are critical across the entire operating temperature range.