Polylobe Turning

Shaft/collar connections with polylobes have many advantages, but producing these cross-sections has always been a highly demanding and fairly unproductive process. Polylobe turning changes this. With this innovative process, outer and inner polylobes with a widely differing number of vertices and various shapes can be produced easily, highly productively, and extremely precisely by turning, without the need for complex special fixtures. Even twisted polylobes are possible.

When using the innovative polylobe turning process, the tools are almost as large as the inner polylobe itself and are accordingly stable. Thanks to the continuous cut, polylobe turning is suitable for both soft and hard machining. The process can be used on all INDEX and TRAUB machines.

These types of polylobe have also been standardized since November 2021.

Process kinematics

In terms of shape, these polylobes are hypotrochoids. These are roulettes that are created when a circle rolls around an inner circle. A 3/4/5-sided polylobe is also called an H3/H4/H5 profile. Some of us may still be familiar with such curves from childhood: the flower-like patterns that are created when drawing with a spirograph are also hypotrochoids.

Polylobe turning makes use of the spirograph principle. Here, the tool and the workpiece rotate in the same direction (e.g., tool CW and workpiece CCW, or vice versa). The polylobe is ultimately created because the tool rotates faster than the workpiece and because the two axes are offset from each other by the eccentricity.


INDEX machine tool


This type of shaft/collar with polylobe connection has been standardized in DIN 3689-1 “Shaft to collar connection - Hypotrochoidal H-profiles - Part 1: Geometry and dimensions” since November 2021.

According to this standard, a polylobe profile with three sides and a minimum circumscribed/maximum inscribed circle diameter of
da = 22 mm and di = 18 mm
is designated as follows:

H3 – 22 x 18

“Polylobes are extremely reliable and very durable, especially for shaft/collar connections. With the INDEX polylobe turning technologies, we have created a tool that allows us to provide our customers with excellent support.”

Dr. Volker Sellmeier is Head of Technology Development at INDEX


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