Screw jacks are the solution for achieving linear motion with medium to high forces at low to medium speeds. They are ready-
Machine designers are attracted to the self-
Screw jacks are made with two design concepts: travelling screw and travelling nut. Both are based around a worm gearbox with cast housings in iron or alumin-
Screw jacks can be connected directly to an electric motor creating a compact linear drive. Standard 3 phase motors are most common. For lower powers DC motors can be used, or servo motors can achieve high performance.
There are many variables to be taken into account when specifying a screw jack. The stroke can be up to 6m and is usually defined in 100mm increments. The orientation of the stroke can be in any direction and forces can be push, pull or both. Pull loads have the advantage that there is no tendency for the screw to buckle. Each size of jack will have 3 or 4 different ratios for the worm gear, and the linear speed range can be extended by choosing between threads with 1, 2 or 3 starts. Increasing the number of starts increases the linear speed and the power required.
Screw jacks selection is heavily influenced by the duty cycle, defined as the op-
There are other performance limits that can come into play and advice may be needed from an experienced Engineer. Ambient temperatures above 25ºC re-
Modular screw jacks with a wide range of options allow designers to specify a close-
Travelling screw and travelling nut designs of screw jack