Leadscrew

Because of the large area of sliding contact between their male and female members, screw threads have larger frictional energy losses compared to other linkages.

[3] Leadscrews are a common component in electric linear actuators.

Leadscrews are manufactured in the same way as other thread forms: they may be rolled, cut, or ground.

A hydrostatic leadscrew overcomes many of the disadvantages of a normal leadscrew, having high positional accuracy, very low friction, and very low wear, but requires continuous supply of high-pressure fluid and high-precision manufacture, leading to significantly greater cost than most other linear motion linkages.

V-threads are less suitable for leadscrews than others such as Acme because they have more friction between the threads.

Their threads are designed to induce this friction to keep the fastener from loosening.

They are the most efficient, having the least friction, so they are often used for screws that carry high power; however, they are also the most difficult to machine, and are thus the most expensive.

[7] They are as efficient as square threads in these applications, but are easier to manufacture.

Due to this low efficiency, they cannot be used in continuous power transmission applications.

[5] Alternatives to actuation by leadscrew include: The torque required to lift or lower a load can be calculated by "unwrapping" one revolution of a thread.

The unwrapped thread forms a right angle triangle where the base is

Using this free-body diagram the torque required to lift or lower a load can be calculated:[8][9] where Based on the

equation, it can be found that the screw is self-locking when the coefficient of friction is greater than the tangent of the lead angle.

[11] When this is not true, the screw will back-drive, or lower under the weight of the load.

If the leadscrew has a collar which the load rides on, then the frictional forces between the interface must be accounted for in the torque calculations as well.

For the following equation the load is assumed to be concentrated at the mean collar diameter (

For collars that use thrust bearings, the frictional loss is negligible and the above equation can be ignored.