Linear roller carriages for profile rail guides with high load capacity

What are linear roller carriages and what are they used for?

A linear roller carriage is the part of a profile rail guide that travels along a hardened rail and transfers the load of a machine assembly to it. The table, bracket, working head or other moving part of the machine is mounted on the carriage, while the rail is screwed to the supporting structure.
Roller carriages are used wherever a linear axis has to carry high forces while maintaining precise, repeatable motion with low friction. Typical examples are machine tool axes, heavy gantries, presses, measuring machines and automated equipment with high moment loads.
The carriage itself does not generate motion. The drive is provided by other elements, such as ball screws, racks, belts or linear motors. The task of the carriage is to guide the assembly precisely along the axis and to take up loads in all directions perpendicular to the direction of travel as well as moments about all three axes.
This category contains carriages only. The matching rails are in the roller guide rails category, and the complete system in the parent category profile rail guides.

How does a linear roller carriage work?

The carriage body contains raceways on which cylindrical rollers roll. As the carriage moves, the rollers travel through the loaded zone between the carriage and the rail and then return to the start of the raceway through a return channel. Thanks to this recirculation, the carriage can perform a stroke of any length, limited only by the length of the rail.
The key difference compared with a ball carriage is the type of contact. A ball touches the raceway over a small area which, in an unloaded bearing, is almost a point. A roller touches the raceway along its length, so the contact area is larger.
The consequences of line contact are:

• higher load capacity for the same external dimensions,
• higher rigidity, i.e. smaller deflection under load,
• better vibration damping in the machine structure,
• greater sensitivity to installation errors, for example to unevenness of the mounting surfaces.

Roller carriages are usually preloaded. Preload eliminates the clearance between the carriage and the rail and increases rigidity, but it also slightly increases friction and the force needed to move the carriage.

Main properties of linear roller carriages

The properties of roller carriages depend on the manufacturer, series, size, body shape, preload and accuracy class. In general, the following applies:

• high static and dynamic load capacity,
• high rigidity in all load directions,
• absorption of moment loads about the longitudinal, transverse and vertical axes,
• precise and repeatable guidance over long strokes,
• low friction compared with plain (sliding) guides,
• choice between flanged and narrow body versions,
• standard, long and, in some series, extra-long versions,
• various preload and accuracy classes,
• seals on the end faces and along the carriage,
• lubrication connections for grease or oil.

The decisive data for the final selection come from the manufacturer's catalogue for the specific series and size, above all the dynamic and static load ratings, permissible moments and recommended tolerances of the mounting surfaces.

Types of linear roller carriages available from M&M Intercom

At M&M Intercom this category contains 450+ roller carriages. They are classified by manufacturer and series, and within a series by size, body shape, preload and accuracy.

Manufacturer	Series available	Sizes
Bosch Rexroth	RWD, RWA	25–65; 65, 100, 125
Hiwin	RGH, RGW, QRH, QRW	15–65; 25–45
FAG INA	RWU	25–65

The largest part of the range consists of Bosch Rexroth RWD series carriages, followed by Hiwin carriages, with a smaller share of FAG INA.

Bosch Rexroth RWD and RWA roller carriages

Bosch Rexroth RWD series carriages are available in sizes 25, 35, 45, 55 and 65. The size is written in the designation with three digits, for example RWD-045 for size 45.
The designation continues with the carriage type. The range includes types FNS, FLS, SNS, SLS, SNH and SLH. According to the manufacturer's nomenclature, the first letter indicates the body shape (F flanged, S slimline/narrow), the second the length (N normal, L long) and the third the height (S standard, H high). FNS is thus a flanged carriage of normal length and standard height, while SLH is a narrow, long, high carriage.
The RWA series extends the range to larger sizes. It includes carriages in sizes 65, 100 and 125 in types FNS, FLS and FXS. These carriages are intended for the heaviest axes where smaller sizes are not sufficient.
Bosch Rexroth carriages are available mainly in preload classes C2 and C3, and individually also C1. A higher number means higher preload and therefore higher rigidity. Accuracy classes are designated by the letters H, P, SP and UP, from high to ultra-high accuracy. Some versions have the DS seal in their designation, which the manufacturer uses for more demanding conditions with contamination present.
The exact meaning of all parts of the designation and the part number (e.g. R185…) should always be checked in the Bosch Rexroth catalogue for the selected series.

Hiwin RGH, RGW, QRH and QRW roller carriages

Hiwin is represented in this category by the RG and QR series. RGH and RGW carriages are available in sizes 15, 20, 25, 30, 35, 45, 55 and 65, and QRH and QRW carriages in sizes 25, 30, 35 and 45.
The letter H in the series designation stands for a carriage without a flange (square body), and the letter W for a flanged carriage. The codes CA and HA for H versions and CC and HC for W versions indicate the length or load class of the carriage; the HA and HC versions are longer and have a higher load capacity.
The preload of the Hiwin carriages in the range is designated ZA or ZB, where ZB means higher preload. All Hiwin carriages in this category are in accuracy class H.
Hiwin describes the QR series as a version in which the rollers are guided in a separating chain that reduces contact between the rollers. Details and differences in load capacity compared with the RG series should be checked in the manufacturer's catalogue.

FAG INA RWU

FAG INA RWU series carriages are available in sizes 25, 35, 45, 55 and 65, in several body and length versions.
These carriages are mainly suitable as replacements in existing machines where a system from the same manufacturer is already installed. Because each manufacturer has its own rail profile, carriages from different systems must not be combined without checking compatibility.

Flanged and narrow roller carriages – what is the difference?

A flanged carriage has a body with a side flange through which it can be screwed from above or from below. The wider support surface makes it easier to mount the table and transfer moments.
A narrow carriage has no flange and is fastened from above. It is suitable for designs with limited space in width.
High versions have a greater overall height from the rail to the mounting surface of the carriage. This is important for replacement, as the new version must match the existing installation height.
When choosing between versions, check:

• the available space in width and height,
• how the assembly is fastened to the carriage,
• the arrangement of the mounting holes,
• the overall height including the rail,
• the length of the carriage and thus its load capacity.

Preload and accuracy classes of roller carriages

Preload determines how tightly the carriage sits on the rail. Higher preload increases rigidity and reduces deflection under load, but also increases friction and sensitivity to errors in the mounting surfaces.
Higher preload is often used on machine tools with high forces and vibrations. For less demanding axes, or for two parallel rails installed with lower accuracy, a lower preload may be more appropriate.
The accuracy class describes the permissible deviations in the height and lateral position of the carriage relative to the rail, as well as the differences between carriages on the same rail. A higher class is required for precision machines, but it also requires more precisely machined mounting surfaces.
Preload and accuracy designations are not uniform across manufacturers. Class C3 from Bosch Rexroth is therefore not directly equivalent to class ZB from Hiwin. When replacing a carriage, always compare the catalogue data.

Applications of linear roller carriages in industry

Roller carriages are the first choice for axes that must carry high loads with high rigidity.
Examples of applications include:

• axes of CNC machining centres, lathes and grinding machines,
• gantry machines and heavy-duty manipulators,
• presses and forming equipment,
• measuring and inspection machines,
• machines for processing wood, stone and plastics,
• welding and cutting lines,
• robot cells with additional linear axes,
• special machine designs with high moments.

For lighter applications and higher speeds, linear ball carriages, which are available in a wider range of sizes, are often sufficient.

Roller or ball carriage – which to choose?

The choice depends on the loads, the required rigidity and the operating conditions.

Criterion	Roller carriage	Ball carriage
Type of contact	line	point
Load capacity for the same size	higher	lower
Rigidity	higher	lower
Mounting surface requirements	higher	lower
Typical use	heavy and rigid axes	general automation

A roller carriage is chosen when loads are high, when vibrations are present or when small deflections under load are required. A ball carriage is often more suitable for lower loads, smaller sizes and where the mounting surfaces are machined less precisely.

Compatibility of carriages with rails

A roller carriage only works with a rail of the same system and the same size. The raceway profile is specific to the manufacturer and series, so a carriage from one manufacturer generally cannot be used on another manufacturer's rail.
When ordering, therefore, check:

• the manufacturer and series of the existing rail,
• the rail size,
• the accuracy class of the rail and carriage,
• how the rail is fastened,
• the overall height of the system.

Rails for roller carriages are in the roller guide rails category, while additional seals, plugs and other elements are among the accessories for rail guides.

Installation, lubrication and maintenance

Because of their high rigidity, roller carriages are sensitive to installation errors. The mounting surfaces must be flat and parallel within the tolerances specified by the manufacturer. Unevenness increases internal loads, friction and wear.
During installation, take into account:

• the reference edge of the rail and carriage,
• the specified tightening torques,
• the parallelism of two rails,
• the cleanliness of the mounting surfaces,
• that the carriage must not be removed from the rail without a mounting rail (arbor) if the manufacturer requires one.

Roller carriages require regular lubrication with grease or oil. The type of lubricant, the quantity and the interval are determined according to the manufacturer's instructions and the speed, stroke, load and environment. Suitable greases and industrial pastes are available in our lubricants range.
In environments with chips, dust or coolant, the condition of the seals is also important. Damaged seals allow contaminants to reach the raceways, which shortens the service life of the carriage.

How to choose the right linear roller carriage?

The selection is based on the requirements of the axis and the existing design. For a replacement, the most important item is the exact designation of the existing carriage; for a new design, it is the load calculation.
When selecting, check:

• the manufacturer and rail system,
• the carriage size,
• the body shape (flanged or narrow),
• the length and height of the carriage,
• static and dynamic loads and moments,
• the required service life,
• the preload class,
• the accuracy class,
• the seal version for the environment,
• the lubrication method.

If the designation on the carriage is illegible, the dimensions of the carriage and rail, the hole pattern and the overall height can help. Based on these data, a suitable version can be found.

Linear roller carriages available from M&M Intercom

At M&M Intercom we offer 450+ linear roller carriages from Bosch Rexroth, Hiwin, FAG INA and others.
Carriages are available in sizes from 15 to 125, in flanged and narrow versions, with different lengths, heights, preload and accuracy classes.
In addition to carriages, our range also includes rails for roller guides, ball rail guides and carriages, linear guide sets of rails and carriages and accessories.
We can help you find a replacement carriage by its designation or choose a version for a new axis. Browse the range or send us the designation and details of your application.

 

Frequently asked questions about linear roller carriages

1. What is a linear roller carriage?
A linear roller carriage is the load-bearing part of a profile rail guide that travels along the rail on recirculating cylindrical rollers. The moving assembly of the machine is mounted on it, and the carriage transfers the load to the rail.
Thanks to the line contact between the rollers and the raceways, the carriage has a high load capacity and rigidity. It is used mainly on heavier and precision linear axes.
2. What is the difference between a roller carriage and a ball carriage?
A roller carriage uses rollers with line contact, a ball carriage uses balls with point contact. A roller carriage therefore has a higher load capacity and rigidity for the same size.
A ball carriage is less sensitive to errors in the mounting surfaces and is also available in very small sizes. The choice depends on the loads, the required rigidity and the accuracy of installation.
3. Can I use one manufacturer's roller carriage on another manufacturer's rail?
As a rule, no. The raceway profile, dimensions and tolerances are specific to the manufacturer and series.
The carriage must match the system and size of the rail. Combining different systems is only possible if the manufacturer explicitly confirms compatibility.
4. What do the designations FNS, SNS or SLH mean on Bosch Rexroth carriages?
The designations describe the shape of the carriage. The first letter indicates whether the carriage is flanged (F) or narrow (S), the second the length (N normal, L long) and the third the height (S standard, H high).
When replacing a carriage, the type must be the same as the existing one, otherwise the installation dimensions and hole pattern may differ. Always check the full designation in the manufacturer's catalogue.
5. What does carriage preload mean?
Preload means that the carriage is fitted on the rail without clearance and with a defined internal load. This increases rigidity and reduces deflection under external load.
Higher preload also increases friction and the requirements for installation accuracy. The range includes classes C1, C2 and C3 for Bosch Rexroth and ZA and ZB for Hiwin. The designations of different manufacturers are not directly comparable.
6. Which accuracy class do I need?
The accuracy class is selected according to the required accuracy of the machine. Higher classes such as SP or UP are suitable for precision machine tools and measuring machines.
A higher class also requires more precise mounting surfaces. If these are not adequate, a higher class will not deliver the expected accuracy.
7. Which roller carriage should I choose for a CNC machine?
For a CNC machine, the carriage is selected according to the cutting forces, the mass of the table, the accelerations and the required rigidity. Preloaded roller carriages in higher accuracy classes are often used.
The size and length of the carriage are determined by calculating loads and service life according to the manufacturer's catalogue. For a replacement, use the same version as the one installed.
8. How often do roller carriages need to be lubricated?
The lubrication interval depends on the speed, stroke, load, temperature and environment. Exact data are specified by the carriage manufacturer.
With central lubrication, the correct quantity of lubricant per pulse is important. With manual lubrication, the carriages are greased via the grease nipple at regular intervals.
9. Are roller carriages suitable for dirty environments?
Yes, provided that suitable seals are selected and lubrication is maintained. Some carriages in the range have the DS seal version, which the manufacturer intends for more demanding conditions.
In environments with chips and coolant, additional protection of the rail, for example with a cover strip or covers, and regular inspection of the seals are advisable.
10. How do I find a replacement roller carriage?
Most reliably by the full designation on the carriage, which includes the series, size, type, preload and accuracy class. For Bosch Rexroth, the part number also helps.
If the designation is illegible, we need the rail manufacturer, the size, the carriage dimensions and the overall height. At M&M Intercom we will help you find the right version among 450+ roller carriages.