Combined needle roller/axial deep groove ball bearings from Schaeffler are playing a key role in ensuring the smooth, quiet motion of kinetic wind-powered sculptures developed by popular UK sculptor David Watkinson.

“I’ve been a full time sculptor for the last 18 years, working from my home studio in Leeds. Although most of my pieces are static, over the last four years I’ve developed three kinetic sculptures that are powered by the wind and small currents of warm air. All of these rely on combined axial and needle roller bearings, precision manufactured by Schaeffler,” says David Watkinson.

Inspired by the great American artist and kinetic sculptor George Rickey (1907-2002), David’s work is sold either to private individuals as garden displays, or to organisations and charities for display to the general public. David has sold sculptures to customers all around the world, from New York to Switzerland.

“Kinetic sculptures are about form and movement,” explains David. “The natural world inspires the form of my work and the unseen forces of nature [such as the wind] dictate its movement. Humans expect movements to be linear, whereas my pieces appear to defy gravity and have very unusual patterns of rotation.

“My pieces are delicately balanced on precision bearings, where small air currents cause large forms such as leaves and seed pods to tip and move in reaction, carving a path through the air before returning to a balanced position. These sculptures represent a perfect combination of art and engineering, with the bearings supplied by Schaeffler being a vital component in the motion system.”

“Four years ago, when I first started developing kinetic sculptures, finding suitable bearings that could provide the appropriate degrees of freedom, as well as enabling smooth, low friction, quiet movements, proved very difficult,” he explains. “However, I suppose my Eureka moment came after I purchased an old George Rickey catalogue from an art gallery in California. This book contained some detailed photographs and handwritten letters to component suppliers, which together helped to explain the complex bearings and counterweight arrangements at the heart of George Rickey’s kinetic sculptures. I therefore began looking for suitable bearings that would enable me to bring my own designs to life.”

For his first kinetic piece, the ‘Kinetic Seed Sculpture’, David spent 18 months experimenting with different types of bearings. Eventually, due to the complex angles of motion needed for the sculpture, he selected a combined roller/axial bearing that would meet his design requirements and so searched on Google for a suitable supplier. “I came across a bearing on Schaeffler’s website that I thought was suitable and started to examine the bearing drawings in more detail. My sculptures are high quality precision-engineered art pieces that sell for between £8,000 and £12,000 each. I therefore needed precision-made, high quality, reliable bearings that would also provide longevity.”

After speaking to Schaeffler UK, David was put in touch with a local distributor of Schaeffler bearings based in Bradford, which provided David with additional technical data and drawings of the bearings. “The first bearings that I fitted to the sculpture worked perfectly. All I needed to do was make some minor adjustments to the Y-piece of the sculpture. I’ve never had a single problem with any of the Schaeffler bearings since,” states David.

The Kinetic Seed Sculpture revolves gently in warm air currents and moves more dramatically in strong winds. The sculpture feathers in the wind and constantly moves smoothly and silently to ‘avoid’ the wind. These movements are possible through the laws of physics that govern pendulums and compound pendulums and by using precision housed ball bearings. Within each of the seed pods and the vertical shaft is a double race bearing, which allows each of the seed pods to rotate 360 degrees in an angled plane, whilst simultaneously allowing 360 degree rotation about the central column. The plinths of the Kinetic Seed Sculpture are made from corten steel, the shaft from cold drawn mild steel and the seed pods from cold cast bronze.

“All my pieces use cold cast bronze. Inside is a matrix of marine resin and fibre glass, which provides a very high strength-to-weight ratio, similar to a canoe or racing yacht.”

In order to bring his kinetic sculptures to life, David requires help from local engineering firms. “I’ve managed to find a couple of local engineering companies in Leeds who help produce other parts of my sculptures. John Fletcher Engineering Ltd, for example, manufactures all the shafts and provides any machining or boring out work. My brother-in-law is a CAD engineer and so I send hand drawn sketches of my sculptures to him for modelling. Some of the more complex shapes of seed pods and leaves require laser cutting or water jet cutting and so I subcontract this type of work to local firms too.”

David’s latest kinetic piece, Orbit, is currently on display near the Visitor Centre at the Royal Horticultural Society’s Hyde Hall in Essex. The sculpture, which stands 4m tall by 3m across, took six months of development effort, prototyping and planning. Orbit consists of two seed-like pods, which gently dip and weave around one another in a slow, graceful dance. The structure of the pods is exposed and the aluminium fins are angled to catch the breeze. Precision manufactured lead counterweights are also provided for perfect balance, as well as three sets of combined needle roller/axial ball bearings from Schaeffler. These bearings are positioned at the junction inside the Y-piece and in each of the arms near to the aluminium plinths.

The bearings supplied to David Watkinson for all three of his kinetic pieces are NKX35Z (35mm inside diameter) and NKX25Z (25mm ID) combined needle roller/axial deep groove ball bearings. The bearings are supplied with separate inner rings and are manufactured to Schaeffler’s premium quality X-life grade. These bearings have optimised raceway surfaces that provide higher load carrying capacity and longer rating life.

Combined needle roller/axial deep groove ball bearings do not have an inner ring and so are extremely compact in the radial direction. However, the bearings require a shaft raceway that is hardened and ground. NKX..-Z bearings have an axial bearing component comprising a ball and cage assembly with a sheet steel cage and end cap on the axial bearing component.

For lubrication, the outer ring has a lubrication groove and holes. The axial bearing component is lubricated with grease using a lithium complex soap grease to GA08.

“As well as supplying the bearings and providing technical support and guidance, Schaeffler has also been extremely supportive in other ways. For example, Schaeffler is now an official sponsor of my kinetic sculpture work.”

For more information on combined axial ball and needle roller bearings from Schaeffler, please call the Marketing Department on 0121 313 5870. Alternatively, email info.uk@schaeffler.com.

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