A linear guide is a machine element that guides a component along a straight path while carrying forces and moments. It consists of a guide rail and a guide carriage running on it. Between the two, rolling elements, running rollers or sliding surfaces ensure that the carriage moves with low friction and high accuracy. Linear guides are the central component of linear technology and are found wherever axes travel, loads are positioned or tools are guided.
This page gives an overview of the types of linear guides, the criteria for selection and the designs that Franke develops and manufactures.
Design of a linear guide
Every linear guide consists of two main parts: the guide rail, which is bolted firmly to the machine, and the guide carriage, which carries the moving load. Depending on the manufacturer, the carriage is also called a slide or cassette. The carriage contains the elements that roll or slide on the rail: recirculating balls, running rollers or sliding pads. Seals and wipers keep dirt away from the running surfaces.
How rail and carriage interact determines the properties of the linear guide: load capacity, stiffness, speed, smooth running and maintenance effort.
Types of linear guides
Linear guides can be classified according to the functional principle between rail and carriage. The four most important types are:
Recirculating ball guides
In a profile rail guide with ball recirculation, balls roll between rail and carriage and are continuously returned inside the carriage. Recirculating ball guides are usually made of steel, achieve high guiding accuracy and stiffness and are therefore widespread in machine tool construction. They are supplied lubricated and relubricated at intervals depending on design and application.
Roller guides
In a roller guide, running rollers roll on the raceways of the rail. The rollers contain rolling bearings. Roller guides run smoothly, are suitable for high speeds and are comparatively insensitive to dirt. Because rails and carriages are often made of aluminium, they are also light.
Plain linear guides
Plain linear guides work without rolling elements: carriage and rail slide on each other via plastic or metal surfaces. They are simple, robust and insensitive to dirt, and versions with plastic sliding elements often work without lubrication. In return, friction is higher than with rolling elements. Lubricated plain guides can also tend towards stick slip, which impairs positioning accuracy.
Shaft guides
In a shaft guide, a linear ball bearing runs on a round, hardened shaft. Shaft guides are inexpensive and easy to install. Because a shaft can bend under transverse load, stiffness is lower than with profile rail guides. For longer strokes, supported shafts are therefore used, usually two parallel shafts to prevent twisting.
Linear guides compared
| Type | Functional principle | Strengths | Limits |
|---|---|---|---|
| Recirculating ball guide | balls recirculate in the carriage | high accuracy, high stiffness | lubrication required, higher weight |
| Roller guide | running rollers roll on the rail | high speed, low weight, insensitive to dirt | larger sizes needed for very high loads |
| Plain linear guide | sliding surfaces made of plastic or metal | robust, insensitive to dirt, often lubricant free | higher friction, stick slip possible |
| Shaft guide | linear ball bearing on round shaft | easy installation, inexpensive | shaft deflection, lower stiffness |
Selecting the right linear guide
Which linear guide suits an application depends on these factors:
- Load: magnitude and direction of the forces and moments about all three axes.
- Speed and acceleration: with high dynamics, low moving mass and smooth running rolling elements count.
- Accuracy and stiffness: required positioning accuracy and permissible deformation under load.
- Stroke and installation space: rail length, installation height and available width.
- Environment: dirt, moisture, clean room, food sector, vacuum or magnetic fields. Here, material, seal and lubrication are decisive.
- Material and weight: an aluminium guide suits aluminium structures and saves weight.
- Maintenance: whether relubrication is required or the linear guide works maintenance free.
The Franke principle for linear guides
Franke transfers the principle of the wire race bearing to linear movements: raceways made of wire are inserted into the aluminium profiles, and large running rollers roll on them. The inserted raceways provide the load capacity, while the rest of the structure can be made of lightweight aluminium. More on the page The Franke principle for linear guides.
- Maintenance free: the needle bearings or ball bearings in the running rollers are lifetime lubricated.
- Quiet: Franke linear guides run with a quiet, even hum and are suitable for noise sensitive applications.
- Homogeneous with aluminium: rails and carriages are made of aluminium. In aluminium structures, temperature related distortions are therefore ruled out.
- Patented guidance: the running rollers have a groove adapted to the wire raceways. It prevents the rollers from shifting on their pins and rubbing against the housing.
Designs
- Profile rail with carriage: consists of only two assemblies, the profile rail and the guide carriage running on it. A wider profile stabilises the base.
- Pair of profile rails with pair of roller shoes: the guide width can be selected freely via the distance between the two rails. The roller shoes are bolted directly to the adjacent structure, so no carriage plate is needed.
Types for different operating conditions
- Type FDA with carriage: standard, quiet and smooth running, made of aluminium with maintenance free, sealed needle bearing running rollers
- Type FDB with carriage: low cost with ball bearing running rollers, inexpensive and suitable for almost all industries
- Type FDC with carriage: corrosion resistant, quiet and smooth running for demanding environments
- Type FDD with carriage: non magnetic, for example for medical technology and electronics manufacturing
- Type FDE with carriage: lubricant free, for food production and clean rooms
- Type FDG with carriage: stainless steel raceways and ball bearing running rollers, robust and economical
- Type FDH with carriage: highly dynamic with angular contact ball bearings for maximum acceleration and speed, for example in pick and place
- Type FDI with carriage: vacuum compatible, with lubricants and materials against outgassing in high vacuum
Suitable accessories include cassettes with clamping. All products at a glance: product overview linear guides
Standard guide or customised linear guide?
For many applications, the right linear guide can be found in the standard range. If installation space, weight, profile shape or material place special demands, Franke adapts rail profiles and carriages individually. Examples are shown on the pages Individual linear guides and Linear guides in lightweight construction.
Applications of linear guides
Franke linear guides are used in mechanical engineering, medical technology, packaging, apparatus and device engineering, robotics and handling, research and development, vehicle construction, power generation and automation technology, among others. Examples are shown in the overview applications for linear guides.
Frequently asked questions about linear guides
What is a linear guide?
A linear guide is a machine element that guides a component along a straight path. It consists of a guide rail and a guide carriage, between which balls, running rollers or sliding surfaces ensure low friction and accurate movement.
What types of linear guides are there?
The most important types are recirculating ball guides, roller guides, plain linear guides and shaft guides. They differ in the functional principle between rail and carriage and thus in load capacity, speed, smooth running and maintenance effort.
What is the difference between a roller guide and a recirculating ball guide?
In a recirculating ball guide, balls recirculate in the carriage, which results in high accuracy and stiffness but requires lubrication. In a roller guide, running rollers roll on the rail. Roller guides run smoothly, are light and are suitable for high speeds.
Are linear guides maintenance free?
That depends on the design. Recirculating ball guides are relubricated at intervals depending on design and application. In Franke linear guides, the rolling bearings in the running rollers are lifetime lubricated, so they work maintenance free.
How do I choose the right linear guide?
The decisive factors are load and moments, speed and acceleration, required accuracy, stroke and installation space as well as ambient conditions such as dirt, clean room or vacuum. For special requirements, Franke provides advice.
Further terms in the Franke glossary: Roller guide | Linear technology | Aluminium guide
Franke also manufactures linear guides individually to your specifications: Individual linear guides