Joke Technology Lapping convex surfaces not a mission impossible

Editor: Barbara Schulz

Germany – Lapping reaches its limits when processing convex or concave surfaces. A special pendulum device retrofitted to conventional surface lapping machines eliminates this drawback. By Hardy Möckl, lapping product manager at Joke Technology.

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Joke's EL 300 lapping machine.
Joke's EL 300 lapping machine.
(Source: Joke)

There is no way to avoid lapping when one hundred percent flatness of a workpiece surface is required. This age-old machining method reaches its limits, however, when surfaces are convex. Manual surface finishing is time-consuming and error-prone – many users modify the contour of the workpiece by uneven contact pressure, thereby jeopardising error-free function.


An alternative to manual surface finishing is the use of special machines. Joke Technology has developed a system for its surface-lapping machines in order to be able to process concave or convex surfaces.

Customer demand drives in-house developments

The impetus to develop a special lapping device came - as often is the case in the field of mould and toolmaking – from the customers themselves. Concave and convex surfaces are called for in injection moulding, for producing reflectors, mirrors, decorative trays, food storage containers or packaging units. Polished curved surfaces are also required in the optical industry and laser technology as well as to measurement and control technology. They are used, for example, to deflect laser beams so that production workflows can be controlled. Other fields to be mentioned include the sectors of medical engineering and prosthetics, such as artificial joint components. Even in the case of apparently flat products, such as coins, the tools need to be slightly concave in order to achieve an optimum result. It only takes a few micrometres before one can no longer speak of flat surfaces and no longer use standard machines.