34 n MACHINE-BUILDING October 2025 www.drivesncontrols.com How to optimise profile and round-rail speeds Depending on your application, high speed is sometimes considered “the name of the game.”When it comes to using profile or round rails as part of linear motion systems, many variables for each can affect your application’s speed. To optimise these rails to achieve your desired speeds, it is vital to be familiar with the design factors that impact the speed of each component. Profile rails, also known as square rails, have three main components: a profile rail, or inner race, which guides the load to the desired position; a bearing carriage, or outer race, which attaches to the load and the rolling elements that enable smooth motion across the rail; and end-caps, which are mounted on both sides of the bearing carriage, keeping the rolling elements contained and circulating (Fig 1). Designers often specify profile rails for their high load capacity and tight accuracy. Their speed potential depends primarily on whether the rolling elements are caged balls, non-caged balls or cylindrical rollers. Ball bearings or rollers? Ball bearings enable the fastest speeds. Designers specify them when they want smooth and quiet motion control. Their spherical geometry facilitates recirculation, enabling operation at speeds of up to 5m/s and acceleration up to 100m/s2. When higher loads are involved, designers might specify cylindrical rollers instead of spherical balls. These are more expensive, but because the rollers are designed to support loads up to 295kN. and not for speed, maximum speeds are reduced to 3m/s and acceleration to 50m/s2. Safety factors may also limit the speeds of roller bearings. They are heavier than balls, which contributes to their load-handling capability. However, if you push the speed beyond 3m/s, you could damage the endcaps or hamper recirculation, relegating them to operate only as plain bearings. Caged or non-caged? Profile rail can also be specified with either caged or non-caged bearings. In caged versions, each bearing is encased as a separate link in a self-lubricating polymer chain. This prevents them from rubbing against each other, enhancing smooth and quiet operation, but it does so at the cost of speed, which is limited by the reliance on the polymer chain. Top speeds are up to 3m/s, Choosing the best type of rail for a machine application can be confusing. Two experts from Thomson Industries – Ojesh Singh, product manager for ballscrews, leadscrews and linear bearings and guides, and Chris Diak, senior automation product sales manager for motion – look at the various options, and assess their pros and cons. Fig 1. Profile rail systems consist of a square (profile) guide rail, bearing carriage and end caps. Image: Thomson Industries The cutter head of this protective film application machine uses a square rail and bearing to index the cutter. Image: Motion.
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