30 n MACHINE BUILDING October 2023 www.drivesncontrols.com Ballscrews or leadscrews: which are best? One question that gets asked repeatedly about linear motion systems is: is it better to use ballscrews or leadscrews?’ Both perform the same task – converting rotational motion into linear movement. However, assuming that they are interchangeable is a mistake, and a potentially costly one. Their design and operation differ, providing each with its own set of advantages and disadvantages. Weighing these up for the application at hand is essential to ensure that your linear motion system performs to the specified criteria. Both leadscrews and ballscrews use threaded shafts which act as the screw elements. A leadscrew – the simpler of the two options – has a threaded mating nut which is in direct contact with the screw. Rotational motion turns the screw, causing the nut to move along in a linear motion, thus converting the motion from rotary to linear. Leadscrews come in a variety of formats with one of the most popular being trapezoidal versions. The screws are manufactured from steel, and the nuts are available in a choice of materials including steel, bronze, brass and plastic. Ballscrews also use a threaded shaft, but incorporate a helical path around which ball bearings move. The ball assembly behaves like the nut. Ballscrews are available in different formats, with rolled and ground types being the most common. Leadscrews: pros and cons As mentioned above, leadscrews are more basic and that is reflected in their cost. Ballscrews can be two to three times the price of a comparable leadscrew. They also do not need a braking system because they are self-locking, which is a further plus point when it comes to cost. This price differential often makes leadscrews the first port of call, but this can be a false economy because the device may not operate well in your application. It’s horses for courses! Apart from a lower purchase cost, leadscrews have the advantage of usually being self-lubricating and they tend to be quieter in operation than ballscrews. They are compact with fewer parts, and are easy to design into systems. Where they don’t score so well is efficiency, which runs at 20–25%, because leadscrews require more torque and a larger motor and drive. They also have higher friction and therefore run hotter. With ballscrews relying on point contact It can be confusing to decide whether a leadscrew or a ballscrew would be a better option for an application you are designing. Japh Humphries, sales and commercial manager at Matara UK, outlines the key characteristics of each technology and the factors that you need to consider when choosing between the two. Leadscrews are more basic and less efficient than ballscrews but cost much less and don’t need brakes
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