The do’s and don’ts of adjusting pillow blocks to optimise precision
Linear ball bushing bearings for high-load, high-speed applications allow for ultra-smooth travel along the shaft with exceptional precision linear motion, but only when the correct clearance is applied between the shaft and bearing. Correct pillow block adjustment is essential for achieving smooth operation, reducing wear, and maintaining linear bearing precision.
If your bearings are not travelling smoothly, you may need to adjust the clearance to reduce preload. Likewise, if they are not precise in their movement, it is likely that the lash needs adjusting.
Simple Steps for Pillow Block Adjustment
An adjustable pillow block has an adjustable inside diameter that allows engineers to reduce the lash, or play, which is the clearance between the shaft and the bearing.
Adjustments to the inside diameter could not be easier. Simply find the adjustment screw and use a hex (Allen) key to loosen it. Make sure the pillow block is mounted to the shaft (you can check this because it will rotate easily on the shaft) and tighten the adjusting screw gradually until the linear bearing just starts to grip the shaft. Correct pillow block alignment during this process is equally important to ensure consistent bearing performance.
Avoid Over-Tightening
Stop tightening the adjustment screw as soon as you feel a slight increase in force when rotating. This indicates zero play (near-frictionless movement) or slight preload (the force acting on the rolling elements), helping to minimise ball skidding and reduce axial play.
Ideally, you should be able to move the linear bearing along the shaft without roughness and rotate it without drag, using only light pressure. This approach helps achieve optimum linear bearing precision and reliable precision linear motion.
The Dangers of High Preload
If you find you cannot move the bearing using only light pressure, the preload is too high. Excessive preload can cause rough operation, shorten bearing life, and potentially damage both the linear bearing and shaft.
Proper linear ball bushing setup ensures the correct balance between preload and free movement, improving bearing life and system accuracy.
Twin Pillow Blocks
When using a twin pillow block, adjust one linear bearing while leaving the other loose. Note the position of the adjustment screw (for example, the 10 o’clock or 2 o’clock position) or record the torque wrench reading for the first bearing, then loosen it and adjust the second linear bearing. Once the clearance in the second bearing is correct, return the first bearing to its original setting.
Following this method ensures accurate pillow block adjustment, proper pillow block alignment, and smooth, repeatable linear motion.
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