A Unique Development
I. The Patent
On June 19, 1982, Hans Ley and Manfred Schmidt filed a patent application at the German Patent Office for a process enabling the manufacture of polygonal profiles through superimposed rotary movements. On June 18, 1983, the European application followed; European Patent EP 0097 346 B1 was granted in May 1988. Further patents followed for the manufacturing process and specific applications, including form-turned cages for rolling bearings.
The process is based on three superimposed rotary movements with nine parameters — a transfer of the epicyclic motions of celestial mechanics to manufacturing technology. It enabled, for the first time, the production of not only straight but also concave and convex window flanks in bearing cages.
II. The Application
At SKF GmbH in Schweinfurt, the German subsidiary of Svenska Kullagerfabriken headquartered in Gothenburg, engineer Alfred Weidinger recognized the process's potential for cage manufacturing. Weidinger joined SKF in 1982 in the department for further development of cylindrical roller bearings. From 1985, he worked in central manufacturing technology for full complement bearings as well as sheet steel and brass cages. From 1990 to 1992, he worked on the "development of form-turned cages" — as formulated in the later laudation by the German Institute for Standardization.
Weidinger advocated for the introduction of the process at the corporate headquarters in Gothenburg. SKF acquired three machines: two manufactured by Heckler & Koch and one by J.G. Weisser Söhne GmbH. The process was operated under the company's highest level of confidentiality.
III. The Numbers
When the machines were first used, the following data applied for a profitability comparison: the investment costs were approximately 30 percent compared to a conventional rotary transfer machine on which the rings were previously produced. The production time was 10 to 20 percent compared to conventional production, with considerably lower tooling costs.
In the conventional broaching process, the flanks of the windows for the rollers could only be produced straight. The new process enabled both straight and concave or convex forms for the first time. The curved shape offers significant advantages: in combination with the high precision that is inherent to the process, the window openings can be made slightly smaller than the diameter of the rollers. The difference lies in the elastic range of the material, so that the rollers can be clipped into the ring without any problems and no longer fall out.
Previously, an additional machine was necessary on which the rollers were caulked by hammer blows on the window edges to prevent them from falling out. This machine became superfluous. Furthermore, the free shaping of the window edges enabled an optimal design of the lubrication zone, resulting in a longer service life of the bearings.
IV. The Catalog
In an SKF product catalog, the one-piece solid brass cage is described as follows:
"The form-turned, one-piece solid brass window cage is a unique SKF development and represents the new generation of solid brass cages for SKF cylindrical roller bearings."
The essential characteristics and advantages listed are: very high strength, particularly good suitability for very high speeds and accelerations, suitability for high temperatures, excellent vibration resistance, particularly lightweight construction, and outstanding lubrication properties through special surface topography.
The inventor of the form-turning process is not mentioned in the catalog.
V. The Honor
On March 30, 2017, on the occasion of the 100th anniversary of the DIN Standards Committee for Rolling Bearings and Plain Bearings, Alfred Weidinger was awarded the Beuth Memorial Medal by the German Institute for Standardization — "for his years of commitment to standardization in the field of rolling bearings."
The laudation traces Weidinger's career at SKF: from 1982 in the further development of cylindrical roller bearings, from 1985 in central manufacturing technology, from 1990 to 1992 the "development of form-turned cages," followed by leadership of manufacturing technology for EXPLORER bearings, from 1998 leadership of product development, from 2007 leadership of product specification, from 2012 leadership of Technical Standards. One of his greatest achievements is cited as the publication of the book on the "development history of the cylindrical roller bearing" (SKF, 2009).
The laudation mentions no external inventor. The name Hans Ley does not appear. European Patent EP 0097 346 B1 is not cited.
VI. The Letter
On July 2, 2025, Hans Ley wrote an email to Annika Ölme, Chief Technology Officer of the SKF Group in Gothenburg. In the letter, he introduced himself as the inventor and first mover of the polygon turning technology used at the Schweinfurt facility. He referenced the three machines operated there and his European patent. He offered to re-establish the business relationship and reported on discussions with Swedish machine builder Modig Machine Tool about a potential partnership. In light of the insolvency of machine manufacturer Weisser, he offered a European solution.
The letter received no response.
VII. The Chronology
1982: Patent application by Hans Ley and Manfred Schmidt. 1983: European patent application (granted as EP 0097 346 B1). From 1985: Alfred Weidinger works at SKF on manufacturing technology for cages. 1990–1992: According to the DIN laudation, Weidinger works on the "development of form-turned cages" at SKF. The following years: SKF operates the technology under highest confidentiality. 2009: Weidinger publishes the book on the development history of the cylindrical roller bearing at SKF. 2017: Weidinger receives the Beuth Memorial Medal from DIN. 2025: Hans Ley writes to the CTO of SKF. SKF does not respond.
The Svenska Kullagerfabriken were founded in Gothenburg in 1907. The company today employs approximately 40,000 people in over 130 countries and generated revenues of around 100 billion Swedish kronor in 2024. Sweden, the home of SKF, is regularly ranked in international studies as one of the most innovative countries in the world — in part because of its culture of collaboration, trust, and fairness.