How does a screw jack work? What is an anti-rotation device? And what exactly is a block travel?

Anyone dealing with screw jacks – whether as a design engineer, purchaser or service technician – will quickly encounter a variety of technical details. In this article, we answer the most common questions – concisely, clearly, and from the perspective of an experienced manufacturer.

What is a screw jack?

A screw jack is a mechanical drive element that converts rotary motion into linear motion. A spindle is rotated via a gearbox (e.g. worm or bevel gear), generating lift – a movement upward, downward or sideways. Ideal for applications where force, precision and reliability are required.
[Further basics can be found in our article “What exactly is a screw jack?”]

How does a screw jack work?

The basic principle is a threaded drive: the spindle rotates, and a nut (or the spindle itself) moves axially. Depending on the spindle type, we differentiate between trapezoidal thread (with sliding friction) and ball screw (with rolling balls between spindle and nut).

What is the difference between translating screw and rotating nut versions?

In the translating screw version, the spindle rotates while the load is moved linearly via a fixed-position nut.
In the rotating nut version, the spindle remains stationary, and the nut moves along the spindle. This version is especially suitable when the spindle must remain fixed while still allowing motion.

What is the difference between trapezoidal and ball screw drives?

That depends on the application – see chart.

Tip: For simple, static applications, a trapezoidal thread is often sufficient. For frequent, fast or highly precise movement, a ball screw is usually the better choice.
Read our comparison: “Trapezoidal vs. Ball Screw”

When is an electromechanical system better than hydraulics or pneumatics?

Whenever high energy efficiency, low maintenance, and precision are required. Electromechanical systems are also cleaner, quieter, and much easier to integrate into digital control systems – ideal for Industry 4.0.
[Our article “Hydraulics, Pneumatics or Electromechanics?” explains the differences in detail.]

What does 'self-locking' mean and when is it important?

A self-locking system holds its position even in the event of power or motor failure, without the need for a brake. Trapezoidal screw spindles naturally offer this feature. This is especially important for safety-critical applications like lifting tables, stages, or protective devices.

What is a spindle brake?

A spindle brake is a mechanical or electromechanical device that prevents a spindle from unintentionally rotating or backdriving – especially after the drive motor is switched off. It is used to hold the load in position and prevent uncontrolled lowering.

This is particularly necessary for non-self-locking systems such as ball screws. While they offer high efficiency and dynamic performance, they cannot generate holding force when unpowered. Without a brake, the load would lower uncontrollably.

Typical types include:

• Motor-integrated brakes (e.g. spring-applied brakes on servo motors)
• External holding brakes acting directly on the spindle or gearbox
• Safety catch systems for vertical lifting applications

Good to know: Screw jacks with trapezoidal threads often do not require an additional brake – the self-locking effect of the thread pairing provides secure hold in any position.

Can a screw jack absorb side loads?

That depends on the design. Standard gearboxes are typically not designed for transverse forces. For applications with lateral loads – such as in material handling or lifting vehicles – we recommend specially supported or telescopic solutions with additional guidance.

What is block travel and how can it be avoided?

Block travel occurs when, in a multi-axis system, one actuator stops while others continue moving – for example, due to overload, malfunction or power loss. This leads to distortion and stress in the overall system. Solutions include torque monitoring, limit switches, standstill detection or the use of safety couplings.

Are screw jacks suitable for continuous duty?

Many standard screw jacks are designed for a duty cycle of 20%. For longer operating times, we offer Enzfelder models with special designs, higher efficiency (e.g. ball screws), and optimized thermal management.

What is an anti-rotation device and what is it used for?

An anti-rotation device prevents the spindle or nut from rotating during axial movement. It can be implemented via:

• Keyways or guide slots
• Square flanges
• External guiding systems

It is required whenever the overall construction does not inherently provide torsional guidance.

Can screw jacks be used outdoors?

Yes, screw jacks are suitable for both indoor and outdoor use. With appropriate seals, lubricants and materials, our gearboxes are designed for operation in environments with extreme heat, cold, moisture or dust. Stainless steel spindles or ATEX options are also available.

Can a screw jack be overloaded – and what happens then?

Yes. Overloading a screw jack can damage the spindle, nut or housing. That’s why we recommend:

• Including safety margins in the design
• Using overload couplings
• Employing electronic monitoring such as torque limiters

Are standardized sizes available?

Yes. Most manufacturers – including Enzfelder – offer standardized series with defined sizes and load ranges from 2.5 kN to over 1000 kN. At the same time, custom solutions are part of our daily business: from stainless steel versions to ATEX-certified designs.

Do you have more questions? We’re happy to help!

This article only covers some of the most frequently asked questions. If you have special requirements or need support with your system design, feel free to contact us. Our team will gladly assist you.

Contact us now