FHS-OCT23-PG36+37_Layout 1 13/10/2023 12:03 Page 36
machine building
perform the same task, converting rotational motion into linear movement. however, assuming they are interchangeable because of this would be a mistake, and a potentially costly one at that. Their design and subsequent operation differ, providing each with its own set of advantages and disadvantages; weighing these up against the application at hand is essential to ensure your linear motion system performs to the specified criteria.
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DeSign anD operation CoMpareD both lead and ball screws feature a threaded shaft which acts as the screw element of the unit. a lead screw - the simpler of the two options
when it comes to design – 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, thereby converting the motion from rotary to linear. lead screws come in different formats with one of the most popular for industrial applications being trapezoidal lead screws. The screws are manufactured from steel and the nuts are available in a variety of materials from steel through to bronze, brass and plastic. in the case of ball screws, a threaded shaft is
also used, but it features a helical path around which ball bearings move. The ball assembly behaves as the nut. ball screws are available in different formats, with rolled and ground types mostly favoured by manufacturers.
LeaD SCrewS: proS anD ConS as mentioned previously, lead screws are the more basic design of the two and that is reflected in the cost. lead screws have a lower capital outlay than ball screws; ball screws can be two to three times the price of a comparable lead screw. They also do not require a braking system as they are self-locking, which is a further plus point when it comes to total cost. This price differential often makes lead
screws the first port of call, but this could be a false economy as it may not operate well in your specific application; it is horses for courses, as the saying goes! apart from a lower purchase cost, lead screws
have the advantage of generally being self- lubricating and they tend to be quieter in operation than ball screws. They are compact with minimal parts, and are easy to design into a system. where they do not score so well is efficiency,
which runs between 20 per cent to 25 per cent, as lead screws require greater torque and a larger motor and drive. They also have higher friction and therefore run at a hotter temperature.
BaLL SCrewS: proS anD ConS with ball screws relying on point contact to support a load, as opposed to line contact, less friction is produced during use. This means that
36 ocTober 2023 | facTorY&handlingsoluTions
hen it comes to linear motion systems, one question that gets repeatedly asked is ‘which should i use – ball screw or lead screw?’ They both
ball screws vs lead screws:
horses for courses By Japh Humphries, UK Sales & Commercial manager, Matara UK
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