LM Guide Raceway Grooves: The Impact of Groove Shape on Performance

Wherever high accuracy and reliability are required, industrial machinery like machine tools, semiconductor manufacturing equipment, and industrial robots contain a critical component that provides smooth, precise linear motion. Known as the LM (Linear Motion) Guide, this component facilitates straight, smooth, and precise motion and contributes greatly to equipment performance and life. It was first developed by THK as a groundbreaking way of incorporating rolling motion in a linear motion part. THK now boasts a full lineup of LM Guide products with a variety of different features, but two things most of our mainstays have in common are circular arc grooves and balls arranged in a DF configuration. This time, we’ll highlight the rationale behind LM Guide groove shape and groove contact structure, explaining the benefits provided by the interplay of these two factors without getting overly technical.

LM Guide Raceway Grooves An LM Guide is composed of three basic elements: a mobile LM block, an LM rail that supports its motion, and balls that roll along what are called raceway grooves. The shape of these raceway grooves is a crucial design factor that impacts the kinematic performance and service life of an LM Guide.

Two-Point Contact vs. Four-Point Contact: Characteristics of Different Groove Shapes An LM Guide incorporates a large number of balls packed into the space between an LM block and the LM rail, and the way these balls make contact with the raceway grooves plays a large role in determining the characteristics of the LM Guide overall. Generally speaking, the grooves of an LM Guide will be one of two shapes. Circular arc grooves The shape of a circular arc groove is defined by a single curve. Balls make contact with these grooves at two different points. Gothic-arch grooves The shape of a Gothic-arch groove is formed by combining two different curves. Balls make contact with these grooves at four different points.

Different Uses for Circular Arc Grooves and Gothic-Arch Grooves In order for an LM Guide to bear both vertical and horizontal loads, its balls must make contact with its grooves at a total of eight different points. The examples below show the structures generally used to meet this requirement. Four circular arc grooves (with two points of contact each) Two Gothic-arch grooves (with four points of contact each)

Gothic-arch grooves are often used for things like miniature LM Guide models in cases where load capacity requirements would otherwise be more constrained by a limited cross-sectional area.