Leadscrews roll over ball screws

Leadscrew technology has made vast strides. Now, leadscrews offer higher performance at lower cost. Leadscrews were once considered a cheap substitute for ball screws to be used mostly in less demanding applications. They were often assembled using low-quality ball-screw or fastener designs, where a simple, one-piece nut provided basic power transmission and rotary-to-linear motion conversion. Today, leadscrews offer many distinct advantages for motion control. For instance, precision thread rolling yields lead accuracy of 0.0001 mm/mm at approximately one-tenth the cost of ground screws in lengths to 4 m. Polymer composite nut materials provide high strength, capable of supporting dynamic loads to 250 kg, long life (over 750 million cm of travel), and can be molded to custom shapes. In addition, antibacklash nuts automatically compensate for wear. Among some of the other benefits are high helix, fast leads (greater than 100 mm/rev) with threads as small as 0.5 mm/rev. Plus, nonbackdriving, self-locking leads and multifunction nuts are easily customized, and can offer zero backlash with light preload and low drag. Leadscrews differ from ball screws in that they use sliding rather than rolling friction between the nut and screw. This leads to quieter operation because of no recirculating ball noise. And modern materials keep friction low, with dynamic coefficients ranging from 0.07 to 0.09, eliminating the need for external lubrication and cutting maintenance costs. Another major concern is the amount of particulates generated and their impact on operation. Metal-on-metal contact with rolling elements has no sliding friction. But imperfections in feature sizes can lead to localized stress concentrations that, over time, create surface imperfections. These imperfections have the cumulative effect of increasing friction stress. This leads to sliding and later brinnelling, which generates significant debris and eventually catastrophic failure. Ground ball screws and bearings start out better. But lower-cost rolled ball screws