The virtues of using a screw as a machine, essentially an inclined plane wound round a cylinder, was first demonstrated by Archimedes in 200BC with his device used for pumping water.
There is evidence of the use of screws in the Ancient Roman world but it was the great Leonardo da Vinci, in the late 1400s, who first demonstrated the use of a screw jack for lifting loads.
Leonardo’s design used a threaded worm gear, supported on bearings, that rotated by the turning of a worm shaft to drive a lifting screw to move the load - instantly recognisable as the principle we use today.
We can’t be sure of the intended application of his invention, but it seems to have been relegated to the history books, along with the helicopter and tank, for almost four centuries. It is not until the late 1800s that we have evidence of the product being developed further.
With the industrial revolution of the late 18th and 19th centuries came the first use of screws in machine tools, via English inventors such as John Wilkinson and Henry Maudsley The most notable inventor in mechanical engineering from the early 1800s was undoubtedly the mechanical genius Joseph Whitworth, who recognised the need for precision had become as important in industry as the provision of power.
While he would eventually have over 50 British patents with titles ranging from knitting machines to rifles, it was Whitworth’s work on screw cutting machines, accurate measuring instruments and standards covering the angle and pitch of screw threads that would most influence our industry today.
Whitworth’s tools had become internationally famous for their precision and quality and dominated the market from the 1850s. Inspired young engineers began to put Whitworth’s machine tools to new uses. During the early 1880s in Coaticook, a small town near Quebec, a 24-year-old inventor named Frank Henry Sleeper designed a lifting jack. Like da Vinci’s jack, it was a technological innovation because it was based on the principle of the ball bearing for supporting a load and transferred rotary motion, through gearing and a screw, into linear motion for moving the load. The device was efficient, reliable and easy to operate. It was used in the construction of bridges, but mostly by the railroad industry, where it was able to lift locomotives and railway cars.
Local Coaticook industrialist, Arthur Osmore Norton, spotted the potential for Sleeper’s design and in 1886 hired the young man and purchased the patent. The ‘Norton’ jack was born. Over the coming years the famous ‘Norton’ jacks were manufactured at plants in Boston, Coaticook and Moline, Illinois.
Meanwhile, in Alleghany County near Pittsburgh in 1883, an enterprising Mississippi river boat captain named Josiah Barrett had an idea for a ratchet jack that would pull barges together to form a ‘tow’. The idea was based on the familiar lever and fulcrum principle and he needed someone to manufacture it. That person was Samuel Duff, proprietor of a local machine shop. Together, they created the Duff Manufacturing Company, which by 1890 had developed new applications for the original ‘Barrett Jack’ and extended the product line to seven models in varying capacities.
Over the next 30 years the Duff Manufacturing Company became the largest manufacturer of lifting jacks in the world, developing many new types of jack for various applications including its own version of the ball bearing screw jack. It was only natural that in 1928, The Duff Manufacturing Company Inc. merged with A.O. Norton to create the Duff-Norton Manufacturing Company.
Both companies had offered manually operated screw jacks but the first new product manufactured under the joint venture was the air motor-operated power jack that appeared in 1929. With the aid of the relatively new portable compressor technology, users now could move and position loads without manual effort. The jack, used predominantly in the railway industry, incorporated an air motor manufactured by The Chicago Pneumatic Tool Company.
There was clearly potential for using this technology for other applications and only 10 years later, in 1940, the first worm gear screw jack, that is instantly recognisable today, was offered by Duff-Norton, for adjusting the heights of truck loading platforms and mill tables. With the ability to be used individually or linked mechanically and driven by either air or electric motors or even manually, the first model had a lifting capacity of 10 tons with raises of 2” or 4”.
Since then the product has evolved to push, pull, lift, lower and position loads of anything from a few kilos to hundreds of tonnes. One of the biggest single screw jacks made to date is a special Power Jacks E-Series unit that is rated for 350 tonnes –even in earthquake conditions for the nuclear industry.
Most features now offered by our competitors were actually designed and patented by Power Jacks and Duff-Norton over the years. The anti-backlash mechanism, for instance, was first designed and introduced in 1967.
More recent developments have concentrated on improved efficiency and durability, resulting in changes in both lead screw and gearbox design options for screw jacks.
As an example, the use of a ball screw instead of the more common machine screw as the lead screw in a screw jack will increase the efficiency of a unit. A ball screw typically has a 90%-95% efficiency rating as the nut runs up and down the screw on a race of ball bearings – significantly higher than the typical 35%-55% efficiency seen in a machine screw that relies on sliding friction between the flanks of the nut and screws threads. These improvements in efficiencies have allowed screw jacks either to use less power and save energy, or to run at faster speeds
However, the use of the ball screw has been limited by its large physical size (for a given rated load) when compared to a machine screw, and by the ball screw’s higher sensitivity to damage in arduous environments. These limitations led to the introduction of roller screw technology to screw jacks, yielding designs such as the Spiracon 2 which is used in variants of Power Jacks’ E-Series screw jack. The roller screw offers high durability, high accuracy and high efficiency in a scalable technology that can cope with the very high loads operated by screw jacks.
Further, screw jack performance is not just about the gear and screw geometry: gearbox design is also a key factor. That is why high thermal efficiency screw jacks, such as the Power Jacks S-Series, have evolved. These units are designed to deliver improved thermal efficiency by optimising the surface area and mass of a screw jack’s gearbox, with oil used as the lubricant instead of the conventional grease-filled gearbox. The result is that units, such as the S-Series, can achieve 50% higher duty cycles than conventional worm gear screw jacks.
Since the 1990s there has also been a visually noticeable change in some screw jack designs, with moves towards a cubic-shaped gearbox. These cubic screw jacks generally offer improved flexibility for mounting, as they are symmetrical and can be mounted on two faces. There is no need for the upright and inverted style options required for single face screw jacks. They also represent an aesthetic alternative to the more common single face design, such as Power Jacks’ E-Series screw jack.
A screw jack that has a built-in motor is now referred to as a linear actuator but is essentially still a screw jack. Today, screw jacks can be linked mechanically or electronically and with the advances in motion-control, loads can be positioned to within microns. Improvements in gear technology together with the addition of precision ball screws and roller screws mean the applications for screw jacks today are endless and a real alternative to hydraulics in terms of duty cycles and speed at a time when industry demands cleaner, quieter and more reliable solutions.
You may be surprised at the extent to which screw jacks are used all around us today. Although normally hidden away, they are an integral part of many machines that impact our daily lives.
Bread, beer, hospital beds, crisps, dentist chairs, crockery, roller-coasters, football stadiums, theatres, aircraft air bridges, mars bars, jumbo jets, paper, steel, glass, aluminium, clean water, plastic, trains, cars, electricity generation, satellite dishes, milk cartons, carpet, coins. These, and many more, all have one thing in common...