The answer to this month’s trouble shooter is provided by Phil Nicholas, business development manager – Linear and Actuation Technology at SKF.

Published:  12 April, 2017

What should I look for when choosing between a ball screw and a roller screw?

Like a ball screw, a roller screw uses a rotating externally threaded shaft to control the linear position of an internally threaded ‘nut’. The difference is in the design of the elements used to transmit the loads and limit friction and backlash.

In a planetary roller screw, for example, a number of threaded rollers are arranged around the shaft and held in position by guide rings at both ends of the nut, whereas in a ball screw an arrangement of recirculating ball bearings within the nut maintain contact with the shaft thread.

While both designs offer low friction and precision, the primary advantage of the roller screw over the ball screw is the former’s superior load carrying capacity due to the greater number of contact points made possible by the roller configuration. A roller screw thus takes up less space than a ball screw to meet a specified load rating. And their superior load capability means roller screws have much longer service lives compared with ball screws.

Because of the interaction of the recirculating balls in a ball screw, rotational speed is necessarily limited. The planetary configuration of the roller screw, however, allows much higher rotational speeds, leading to faster linear travel of the nut.

Choosing between a ball screw and a roller screw will depend on a number of factors. Price is certainly a consideration, as roller screws are often an order of magnitude more expensive than common ball screws. Costs aside, a roller screw will always be the technology of choice for space-restricted applications that demand high speeds and high load capacities.

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