The Self-Adjustment Capability of the DF Configuration: Two-Point Contact That Absorbs Mounting Error

No matter how accurate an LM Guide may be, installing it on an actual piece of equipment may introduce some degree of error or tilt. This is where the DF (face-to-face) configuration of the balls comes into play. In a DF configuration, four rows of balls are split into two pairs such that the rows in each pair face each other and their lines of action from applied load converge toward the center of the system.

In a DB (back-to-back) configuration, however, the lines of action from loads applied to rows of balls facing each other converge away from the center of the system.

The self-adjustment capability (the ability of an LM Guide to absorb mounting error inwardly) is the most valuable outcome of combining circular arc grooves with a DF ball configuration. The orientation of the balls inside an LM block makes it possible to absorb error or tilting* on the surface to which the LM rail is mounted without generating an internal load. This limits any increase in rolling resistance, makes it easier to maintain stable motion, and helps prevent diminished service life.

Combining Circular Arc Grooves with a DF Ball Configuration Using circular arc grooves together with a DF ball configuration provides three benefits that are critical for equipment design: 

 Smooth kinetic performance 

Long service life 

Mounting error absorption

Using a Deeper Understanding of Groove Shapes to Select the Optimal LM Guide While this article took a closer look at the features of circular arc grooves used in some types of LM Guide, there are also many instances where the application or design conditions favor the compactness of miniature LM Guide models made possible by Gothic-arch grooves instead. Both groove shapes have a proven record of being useful in different situations. While groove shape may seem like a minor factor, as a design consideration, it has a major impact on equipment performance. Understanding the pros and cons of each groove shape is key to picking the right LM Guide for a given application.