Linear Bearing Guides

A linear guide leaves travel along one axis

A linear bearing guides sliding motion just as a rotary bearing guides turning. Let x point along the travel. The guide supports transverse loads and, where its geometry allows, resists moments that would tilt or twist the carriage. A screw, belt or other actuator supplies travel force; the guide does not drive itself.

In the ideal model, translation along x is free. The desired constraints depend on whether rotation about x is acceptable. Real guide selection also checks load, moment capacity, stiffness, clearance, lubrication and alignment.

A round shaft does not provide an anti-rotation key

A plain round sleeve or linear ball bushing guides motion along a cylindrical shaft. In the ideal geometry it leaves two freedoms: T_x and R_x. The four other motions are restrained by the support's length or spaced bearings. A second parallel guide can stop the carriage rotating.

Geometric freedom is not a rotary service rating. A recirculating ball bushing may resist or wear under rotation even though its round shaft provides no positive anti-rotation feature. Use a product explicitly rated for combined linear and rotary motion when both are required.

LMU is a common catalog family label associated with round-shaft linear ball bushings. Treat it as a catalog name, not a universal standard or proof of rotary capability. Check the supplier's construction, dimensions and limits.

A profile rail constrains twist as well as sideways motion

A shaped rail and matching carriage have separated contact paths that resist twisting and tipping. Within their moment ratings, they leave one degree of freedom: T_x. Mounting surfaces must keep the rail aligned; adding constraints can also make an assembly sensitive to misalignment.

MGN commonly identifies a miniature, narrow-block profile-guide family. For example, HIWIN uses MGN within its miniature MG series, with recirculating balls. The label does not make every supplier's product interchangeable, and does not describe every plain or roller guide.

Opposed V-wheels guide a carriage; one wheel does not

A V-groove wheel runs on a matching edge or rail. A stable carriage commonly uses three or more wheels with contacts opposed across the rail and spaced along it. A triangular three-wheel arrangement can use an adjustable wheel to take up clearance.

The assembled carriage should leave only travel along the rail. Three wheels placed arbitrarily do not guarantee that result: orientation, spacing, contact retention and adjustment determine which loads and moments it can resist. A carriage that can lift away from its track has not constrained that motion.

Compare rotary support on Bearing Types and Loads. Practice counting freedoms