Linear Guide Rail Preload Level

- May 21, 2020-

Linear guide rail preload level

Preload of linear guide: The so-called preload is to give the steel ball load in advance, and use the negative gap between the steel ball and the bead to give preload, which can improve the rigidity of the linear guide and eliminate the gap.

When the working parts of the machine tool move, the steel balls circulate in the groove of the slider, and the load of the slider is distributed to each steel ball, thereby extending the service life of the linear guide. In order to eliminate the gap between the slider and the guide rail, pre-loading can improve the stability of the guide rail system. The pre-loading is obtained by installing an oversized steel ball between the guide rail and the slider. The tolerance of the steel ball diameter is ± 20 microns. In 0.5 micron increments, the steel balls are sorted and sorted and installed on the guide rails respectively. The size of the preload depends on the force acting on the steel balls.

[Guide Slider] Preload level of linear guide slider

According to the size of the preload, it can be divided into different preload levels. The pre-pressure varies from a gap to 0.13c. The C value is the dynamic rated load. In the selection process, you can return to the previous step at any time according to the calculation results to re-select and set. When calculating the maximum load of the slider, it should be confirmed that the static safety factor of the selected linear guide should exceed the value listed in the recommended table. The preload levels of the linear guide slider are: light preload, medium preload, medium preload, and overweight preload.

Overweight preload: high rigidity is required, and the shock force is large, such as the z axis of the working machine and the applicable machinery for heavy preload.

Heavy preload: high rigidity, high vibration and impact equipment, high load and heavy cutting machine tools. For example, machining center, NC lathe, grinding wheel feed shaft, milling machine, vertical or horizontal bed, tool guide.

Intermediate preload: a device with cantilever load or torque, a device for single-axis use, a device with light load and high precision. For example, the feed axis of the grinding machine table, automatic coating machine, industrial robot, NC lathe, EDM machine, measuring instrument, precision XY stage.

[Guide Slider] Preload level of linear guide slider

Light preload: It is suitable for devices with a certain load direction, small vibration and impact force, and two axes used in parallel. The precision requirement is not high, and the equipment with low sliding resistance is only required. For example, beam welding machine, binding machine, automatic packaging machine, XY axis of general industrial machinery, automatic door and window processing machine, welding machine, fuse machine, tool exchange device, various material supply device, CNC engraving and milling machine, light milling machine

If the selected linear guide has insufficient rigidity, you can increase the preload, increase the size or increase the number of sliders to increase the rigidity. The static safety factor is defined as the ratio of the static rated load to the working load. It is worth mentioning that the two-row Goethe-style linear guide pair can withstand the forces and moments in all directions, and it is often used in light or medium load applications, especially when the lateral force load is large. The linear guides with four-row circular arc structure are often used in heavy or super-heavy applications, and the circular arc type has the ability to absorb assembly surface errors. However, if there is an impact load, the linear guide pair of Goethe type structure should be used.