A Practical Look at Load, Preload, Installation, Rigidity, and Long-Term Accuracy A linear guide block rarely gets much attention when a new CNC machine is being designed. The ball screw gets discussed. The servo motor gets sized. The controller and encoder are carefully specified. The guide block? It is often selected by rail width and load rating, then forgotten. That usually works—until it doesn't. A guide that feels perfectly smooth during commissioning can develop higher running resistance, vibration, or positioning errors after thousands of operating hours. In some cases, the guide itself isn't even defective. The problem started with the original selection or installation. After working with linear motion systems, I've found that most guide problems come down to a handful of decisions made before the machine ever runs. Here are seven of the most common ones.