Single or Double Nut, Preload, Rigidity

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This section deals with the various nut types and their preload. We also explain the different rigidity (stiffness) values and why they often cannot be directly compared.

Single or double nut, lead offset, pitch-shift, ball oversize preload
How much preload is needed and recommended
Rigidity

Technical Tip

Preload primarily serves to eliminate play. But at the same time preload increases rigidity, which means the displacement of the nut under load is reduced.

Another reason why preload may be necessary is to prevent balls from skidding during high acceleration, or to ensure better load distribution if side loads on the ball nut cannot be avoided.

There are a number of ways to preload a ball nut. For a discussion of preload and its effects we have to first distinguish between preload with two contact points per ball (one in the nut, one in the shaft), and preload with 4-point contact (two contact points in the nut and two in the shaft), which requires the use of a "gothic arch" profile.

Steinmeyer always uses a gothic arch profile, so both kinds of preload are possible.

FAQ - Preload & Rigidity

What is preload in ball screws?

Preload refers to a controlled axial force applied between the shaft and nut of a ball screw assembly. This preload force ensures continuous contact between the balls and the raceways, eliminating axial backlash and establishing stable, predictable motion control.

Why is preload applied?

Preload significantly enhances critical performance characteristics of ball screws. It increases axial stiffness, improving precision and responsiveness during motion. By eliminating backlash, preload ensures higher repeatability, which is essential for positioning accuracy. In dynamic applications, preload prevents ball skidding during rapid directional changes and reduces system vibrations.

How does preload affect stiffness?

Higher preload levels directly increase ball screw stiffness. Preload minimizes elastic deformation between the nut and shaft under load, resulting in more precise force transmission and positioning behavior. The required friction torque increases proportionally with preload level.

How does preload impact friction, heat generation, and efficiency?

As preload increases, contact between balls and raceways intensifies, leading to higher friction torque and increased heat generation. While some heat dissipation occurs naturally, the optimal preload setting balances maximum precision with high energy efficiency and extended service life.

How do I determine the correct preload for my application?

Preload selection depends on your specific operating parameters: load profile, desired stiffness, travel speed, and operating temperature range. The goal is to achieve preload that minimizes backlash without causing excessive friction or heat buildup.

Steinmeyer provides comprehensive technical consultation, precise service life calculations, and expert support for optimal ball screw dimensioning – ensuring maximum performance and longevity.

What are the differences between single nuts, double nuts, and ETA+ technology?

Single nuts use ball oversize preload to create 4-point contact between balls and raceways. They offer cost-effectiveness and compact design. However, preload is only limitedly adjustable.

Double nuts feature all nut versions where preload is generated through 2-point contact between balls and raceways (e.g., UNILOCK systems or pitch-shift versions). Preload is precisely adjustable, enabling maximum stiffness.

Steinmeyer's exclusive ETA+ technology achieves measurably superior performance across all parameters through specialized ball screw design. Benefits include 50% higher stiffness (compared to conventional double nuts), significantly reduced friction, minimal heat generation, and elimination of backlash.

How does preload influence ball screw service life and load capacity?

Properly dimensioned preload stabilizes load distribution, prevents ball loading through side forces, and protects raceways. Excessive preload increases abrasive wear and can thereby reduce service life.

The influence on load capacity and service life depends heavily on the balance between preload force and external loads. Our application engineers support you with expert consultation, precise calculations, and customized solutions for your specific requirements.