POWER TRANSMISSION REFERENCE GUIDE
The straight story on
ball screw standards
B
all screws are a mainstay of many motion systems. They differ from other types of screws by using balls that roll between a nut, the screw, and helical grooves in the screw, with the balls in effect carrying the load. Ball screws commonly have higher load capacities than comparable lead screws. They’re also a better choice for uses requiring high accuracy. And because ball screws operate on point contact to transmit load, versus sliding elements that are line contact, they inherently have less friction and thus are more efficient, typically to 90% or better. There are several different standards that govern various aspects of ball screw design, from lead accuracy and load capacity to ball nut tolerances and rigidity. However, in many cases these standards are in harmony and provide the same (or virtually equivalent) specifications.
But in the areas where the standards diverge and the specifications differ, it can be difficult for engineers and designers to compare products and choose the ball screw that meets their design and application requirements. So until the industry comes together and adopts a single, international standard, here’s a guide to the similarities and differences between the most commonly used ball screw standards: DIN, ISO, and JIS. DIN (German Institute for Standardization) ISO (International Organization for Standardization) Originally two separate standards, DIN 69051 and ISO 3408, the DIN and ISO ball screw standards have been mostly combined and harmonized. The harmonized standard is referred to as “DIN ISO 3408,” which means the ISO standard has been adopted directly as the DIN standard. The DIN ISO 3408 standard consists of four sections: DIN ISO 3408-1: Ball screws – Part 1: Vocabulary and designation DIN ISO 3408-3: Ball screws – Part 3: Acceptance conditions and acceptance tests DIN ISO 3408-4: Ball screws – Part 4: Static axial rigidity DIN ISO 3408-5: Ball screws – Part 5: Static and dynamic axial load ratings and operational life
Ball screws with nut cooling, shown here from NSK, help machine tool systems run faster and more precise. Piping is attached to the outer periphery of the nut flange, which eliminates the need for sliding seals and rotary joints. This design achieves a cooling capacity greater or equal to existing hollow-shaft ball screws.
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DESIGN WORLD — MOTION
Ball Screws — Power Transmission HB 05.19_v2.indd 10
5 • 2019
motioncontroltips.com | designworldonline.com
5/14/19 7:59 AM
