What should you consider when mounting linear guides?

Linear guides are designed for applications that require precise motion with high load bearing capacity.However,improper mounting can add unnecessary load,shorten service life,and destroy the inherent travel accuracy of a linear guide system.Understanding and following the three mounting specifications described below will help ensure that your installation achieves the required accuracy and does not fail prematurely.

●Rail parallelism

Parallelism between rails,P1

The most common linear guide installation is a two-rail,four-carriage arrangement.However,regardless of the number of carriages,when two guideways are used in parallel,additional lateral loads can occur if they are not installed within the manufacturer's specified parallelism tolerance,usually denoted as P1.There are several options for securing the rails and ensuring their straightness,from the most accurate method of using machined reference edges for each rail,to the least accurate(and least expensive)method of mounting one rail using straight edges or gauges,to"floating" the second rail into proper alignment using a connecting plate.

Be sure to note that the allowable side forces may be reduced if the rail is not mounted on a reference edge or retaining strip.This is because when there is no lateral retention,the shear strength of the rail mounting screws becomes the limiting factor for the allowable side load.

●Vertical offset between rails

Vertical offset between rails,S1

Guideways used in parallel should also observe the maximum permissible offset in the vertical direction.This is usually specified as S1 and is a function of the distance between the rails and the preload of the carriages-the higher preload level of the carriages,the lower the permissible vertical offset.If this value is exceeded,a rolling moment will be introduced into the carriages,which may result in shorter bearing life.

When calculating the vertical offset,the height tolerance,H,of the carriages must be taken into account.If the inclusion of the height tolerance results in an offset greater than the permissible offset,a carriage with a lower preload or a higher accuracy should be used.

●Vertical offset between carriages

Vertical offset between carriages,S2

When multiple carriages are used on the same rail,the vertical offset between the carriages(usually denoted as S2)becomes an important factor and can create pitch moments on the carriages.The allowable vertical offset is a function of the carriages length(standard,short or long)and the distance between the carriages.

Similar to the offset between rails,the calculation of the vertical offset between carriages should take into account the height difference between carriages,ΔH.if the actual vertical offset is greater than the calculated permissible offset S2,a shorter version of the carriages or a higher precision version must be used.

Of course,proper mounting involves other factors,many of which are not directly related to the components used,such as base preparation,reference edge geometry,and even the procedure for tightening mounting screws.Less demanding applications can often be performed satisfactorily with less stringent mounting procedures.However,for the most critical and highest precision installations,strict adherence to the manufacturer's mounting and installation specifications will ensure the highest possible accuracy and avoid shortening the life of the system.

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