T e c h n i c a l i n f o r m at i o n The following chapters only show a small portion of the wide field of applications for ball screws. In order to meet all the technical and commercial demands for such a wide variety of different tasks, a deep understanding of the technology of ball screws is absolutely necessary. We have collected extensive information about ball screws in this section of this catalogue and hope that you will find it useful. Please be aware that although we edited this information as carefully as possible, we cannot be held responsible for missing or incorrect information....

Precision (Lead Error, Friction Torque, Critical Tolerances) Under the headline „precision" DIN / ISO standards are explained as they apply to ball screws, how accuracies are defined, and the acceptance or specification criteria derived from these standards. Lead accuracy Friction torque Roundness, concentricity and squareness of relevant surfaces In general, all acceptance criteria should be reviewed and agreed upon between Steinmeyer and our customer. This is especially relevant for those applications where special demands are required, for example a lead accuracy of class 5 but friction torque...

Positioning ball screws P Transport ball screws T The DIN standard differentiates between positioning ball screws and transport ball screws. Positioning ball screws are normally used in high-precision applications (like machine tool) and are usually equipped with a ground ball thread. Transport ball screws are predominantly used for travelling and moving applications. Typical applications are axes for handling systems. Ball thread of such screws is usually rolled or whirled. Per DIN standard the tolerance classes for positioning ball screws are described as "P" while the transport ball screws...

Lead error fluctuation over entire travel Accuracy class [¹ n/a for rolled and whirled ball screws] Technical Tip The fluctuation of the lead error is defined by two lines parallel to the line representing the average lead error, which include the entire lead error graph. The lead error fluctuation is applicable to precision ground positioning screws in accuracy classes 0 - 5 only. It does not apply to general purpose screws which are typically either rolled or whirled in classes 5 - 10. Lead error fluctuation per 300 mm The variation over 300 mm is the most common definition. However it is also...

Lead error fluctuation over one revolution (lead wobble) The variation of the lead within one revolution, the so-called wobble-error usually is sinusoidal. Here the DIN standard allows relatively coarse tolerances. If needed, this tolerance can be restricted. Limit v2πp for the lead error v2πa [µm] [¹ n/a to rolled or whirled ball screws] Accuracy class Ball screws are globally defined by the ISO standard 3408, which is compatible to DIN 69051 to a large extent. In Japan the JIS 1902 standard is valid while in the USA the ANSI standard B92.1 is still occasionally used. Concerning nut dimensions,...

The friction torque tolerance is solely defined for preloaded ball screws with double nuts and is mainly affected by the accuracy class, preload value and diameter/length ratio of a ball screw. The permissible torque fluctuation is given in % based on the nominal idling torque of a preloaded ball screw. Variation of friction torque Friction torque (nominal) Friction torque variation in [%] Accuracy class For short screws (L ≤ 40 · dN) For longer screws see table below! Friction torque (nominal) Friction torque variation in [%] Accuracy class The values of the interclasses can be determined by...

GENERAL GEOMETRIC TOLERANCES The values listed below represent general rules for run-out tolerances of ball screws. (ACCEPTANCE CRITERIA) 1 ' For specific applications tolerances may vary. Tolerances of run-out Steinmeyer recommends supporting the screw using the outside diameter for all ins- pection of geometric tolerances. This will ensure optimum repeatability of the measu- rement. In some cases the center holes are used as reference. Accuracy class

Accuracy class Accuracy class Run-out of pilot diameter t6 [µm] Nominal-∅ Accuracy class Steinmeyer‘s specified parameters for concentricity and perpendicularity are considerably lower compared to the DIN val

Run-out Tolerance t5p of the shaft outside diameter for the length l5 (the shaft straight- Run-out tolerances ness with reference to AA') - according to DIN 69051 part 3 or ISO 3408-3. Run-out tolerance t 5 p for the length l5 [µm] dN Accuracy class l1 Run-out tolerance t 5 max for the length l1 ≥ 4l5 [µm] l5 Accuracy class Technical Tip Steinmeyer recommends supporting the screw by using V-blocks for all inspection of geometric tolerances. This will ensure optimum repeatability of the measurement. If necessary, dual gages can be used to measure the concentricity of two surfaces with respect...

Mounting Tolerances Technical Tip Steinmeyer recommends maintaining the mounting tolerances shown on this page. Optimum alignment of the screw with the guideways and square and concentric mounting of the nut will ensure proper operation of the drive system and long life of the ball screw. After installation, check that the screw spins freely and without excessive friction over its entire travel. If there is any binding or considerable increase in effort necessary to turn the screw, especially near the support bearings, this indicates the alignment of the screw and the guideways should be improved....

This section deals with the various nut types and their preload. We also explain the different rigidity (stiffness) values. 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...