Screw Jacks
For Any Industrial Application.

A Screw Jack (often referred to as a Jack Screw) is a device used to lift or position heavy objects, components, or platforms by exploiting the mechanical advantage of a lead screw.

They are a popular tool in industry that allows us to leverage an energy-efficient geared lead screw to amplify axial force. Loads of greater magnitude can be moved by converting motion from rotational to linear. The linear motion they provide is achieved via a lead screw which runs through a worm wheel, mated to an input worm shaft. As the attached input drive shaft rotates (either manually by a hand crank or electric motor), it forces the worm gear set inside to rotate. As the wheel turns it translates a lead screw along its internal thread - thus delivering the desired linear movement.

Screw jacks are used around the world for many different industrial applications. They are often more cost effective to manufacture than alternative pneumatic or hydraulic solutions and their simplicity allows for a reduced footprint. They are easy to maintain and, without the need for harmful fluids, there is no risk of hazardous spillages or leaks. They can also easily be synchronised with multiple other units, through the use of driveshafts and gearboxes, to provide a single, modular system. 

Lead Screw Variations

There are three main variations, that we can offer, when choosing a suitable method of translation. Each lead screw and paired 'nut' will have specific advantages and disadvantages which must be analysed to ensure proper operation and performance. Your choice depends on your objective and the nature of your actuation needs.

Trapezoidal Screw

A trapezoidal lead screw allows for translation of motion from rotational to linear. This is achived through continuous contact of two mating threads. The friction between these threads is usually sufficient to provide self-locking properties and prevent back driving. This is dependent on the lead angle, number of starts, and any external conditions the set-up is subjected to, such as vibration.

Ball Screw

In this design, continous contact of two threads is replaced with a ciruit (or several) of ball bearings inside of a ball-nut. Ball screw jacks offer strong operational efficiency, higher travel speeds and increased durability under load due to the lower friction coefficients. Rolled or ground variations are available depending on your precison requirements. The high precision machining involved in their construction means they are expensive to manufacture. Their high efficieny means they are not inherently self-locking and may require an additional locking mechanism or brake to prevent back-drive.

Roller Screw

Roller screws operate in a similar fashion to ball screws but rather than using ball bearings, high precision ground satellite rollers orbit the lead screw. These rollers provide a large number of contact points compared to other lead screw designs, enabling heavier loading whilst maintaing a very high efficiency.

Their smooth translation allows them to provide superior positioning accuracy and enable very high running speeds. The complexity of their construction increases the cost of these units but they will provide the optimal solution in a scenario where high load, travel speed, and precision are paramount.

Motion Variations

All models of Screw Jack and Actuator employ one of the following three motion types.These variations define the way that the lead screw reacts upon connection with the rotational input. Each method of translation will have its benefits over the others in any given scenario.

Translating

In a standard translating screw jack, the rotational input from a worm wheel acts directly on the lead screw, causing the screw to spin if not restricted. If the end of the lead screw , and the jack/actuator body is then fixed in position, the initial rotational input is translated into linear motion as the screw will travel along the thread and through the worm wheel.

Translating Keyed

The dynamics of a keyed setup are similar to a standard translating arrangment but the lead screw itself is instead ‘keyed’ so that it cannot rotate. This restriced motion ensures that all motion is linear, regardless of the mounting arrangement. Keying can be achieved in a number of ways such as using guide rails, linear keyways, or  keying blocks. This type of motion is important if the lead screw end is not to be fixed to the load being lifted.

Rotating

With a rotating arrangement, the lead screw is fixed to the worm wheel and hence only rotation can occur. Linear travel is then achieved using a travelling nut. If this nut has a fixed rotation, it will travel along the lead screw thread,however if not restricted, it will rotate with the worm wheel. 

To build a modular lifting mechanism, the jacks themselves need to be connected to an electric motor or manual input. The motor or hand-crank provides the initial rotational energy which is translated and then converted into linear motion by the connected units.

Most systems are comprised of several jacks linked together by drive shafts, couplings and bevel gearboxes. This modular style of connection is extremely flexible as design engineers can customise a system to suit their needs – including different lifting actions, travel speeds, and load capacity.