A Linear Rail and Carriage assembly consists of two main parts. The first part is the Linear Rail, which is machined to a high precision. The rail can have various profiles, with the most common being either round (a linear shaft) or an “I” shape (the more typical for a rail). The second part is the carriage, of which there may be more than one on a rail. The carriage is designed to fit snugly onto the rail profile, and whilst there are various designs available, it is common for the carriage to have a flat top with mounting holes. For a linear shaft, the carriage is cylindrical and is more commonly referred to as a Linear Bearing or Linear Bush. If a flat top is required, then the bush can be fitted into a housing providing a mounting surface.
There are two basic design concepts that are common in both the Linear Carriage and the Linear Bush. The first is known as the “recirculating ball” type, where there are multiple tracks of steel balls (usually two tracks in a carriage, one either side, and at least four tracks in a Linear Bush at 90 degree intervals around the bore). The second type is a “dry” type, where instead of moving parts (such as the balls) within the Linear Carriage or Bush, a low-friction lining such as PTFE (Teflon®) is used instead.
Regardless of which type of carriage is used, the purpose is to allow the carriage to move smoothly and precisely along the rail with minimum resistance. The applications for Linear assemblies are numerous, especially in automated manufacturing where precise placement of a product is required for assembly or inspection, such as the manufacture of electronic products. An example of a Linear Assembly being used in the home would be in an ink-jet printer, where the print-head move back and forth on a Linear Rail assembly (usually driven by a Timing Belt) allowing for the precise positioning of the print-head.