In brief
A linear guide is a machine element that guides moving assemblies precisely along a straight axis while absorbing forces and moments.
Contents
What is Linear guide?
Linear guides enable straight-line movements with low friction and high repeatability. The most widespread are profile rail guides: a carriage runs on a hardened rail, with balls or rollers circulating in its recirculation channels. There are also shaft guides with linear ball bushings, plain slideways, and roller and track roller guides for long travel and harsh environments. They largely determine the accuracy of a machine.
Recirculating roller guides are stiffer and have a higher load capacity than recirculating ball guides and are preferred in machine tools. Important parameters are size, rail length, carriage type (flanged or narrow, short or long), load ratings, preload class and accuracy class. Preload determines stiffness, and the accuracy class the tolerances of height and parallelism. Wipers and seals protect the recirculation channels from chips and coolant.
Linear guides are found in machine tools, handling equipment, packaging machines and measuring systems. Causes of failure are inadequate lubrication, contamination, damaged wipers, installation errors on the rail mounting surface and overload due to collisions. Repair is usually limited to replacing carriages, wipers or lubrication units; damaged rails, by contrast, must be replaced and realigned.
In practice: maintenance and procurement
To replace a carriage, the size, carriage type, preload, accuracy class and the associated rail must be known. Not every carriage fits every rail of the same system, so it should be checked whether carriage and rail are marked as interchangeable.
Synonyms and abbreviations: profile rail guide · linear motion guide · linear guideway · linear rail · linear bearing system
Frequently asked questions
What is the difference between recirculating ball and recirculating roller guides?
In a recirculating ball guide, balls carry the load via point contact; in a recirculating roller guide, cylindrical rollers do so via line contact. Roller guides are stiffer, carry more and damp vibration better; they are common in metal-cutting machines. Ball guides run with less friction and more easily and are suited to fast, less heavily loaded axes, for example in handling and assembly.
Can just the carriage be replaced?
Yes, if the system is designed for this and the rail is undamaged. Many manufacturers offer interchangeable carriages and rails in certain accuracy and preload classes. For high-precision or matched systems, however, carriage and rail are intended to be replaced together. Running marks or pitting on the rail require it to be replaced.
What information is needed to replace a linear guide?
Needed are the complete type designation of carriage and rail, that is, size, carriage type, preload and accuracy class, rail length, hole spacing and type of fastening. Special features such as additional wipers, lubrication connections or corrosion protection are added. Without a designation, rail width, carriage height, flange dimensions and photos help.
How often does a linear guide need to be lubricated?
The interval depends on load, speed, stroke and environment and is specified by the manufacturer as a travel distance or time period. Short-stroke applications and environments with coolant often require more frequent lubrication. Many machines have a central lubrication system whose function should be checked regularly, as inadequate lubrication is a common cause of failure.