How to Choose Guide Rail?

4 steps to select your linear guide rail ? You also call it guide, linear guide,  sliding rail or telescopic rail but you don’t know which one to choose? Morevover CHAMBRELAN offers you 30 references, 3 different materials and a huge choice of lengths, runners, and options depending on the use…
First of all, let’s define what a linear rail is:

A linear rail consists of a runner, with recirculation ball bearing or rollers, which slides inside a rail.

 

This 4 steps guide help you in selecting THE linear guide you need!

 

We also invite you to discover on our Youtube channel a video presentation of our different linear guide rails

Contents :

1. Rail Lengths and travel
2. Ball bearing or roller runners and load capacity
3. Materials
4. Options

1-  Rail length and stroke

First of all you need to determine the length of the guide rail you need for your installation.

• • You know the travel length; this is your first piece of information,
  • Depending on the size or mass of the device to be moved, you can guide it with 1, 2 or more runners per rail. The space used by all the runners must be taken into account,
  • The rails are equipped with end stops, so this dimension must also be taken into account.

Thus, the dimension of your linear guide rail will be:

    Dimension used by the linear bearing runners
+ Stroke Length
+ Dimensions of the end stops

= Minimum overall length of your guide rail

We offer several types of lengths:

Just ask us and we will provide you with the linear guide you need! CHAMBRELAN offers you:

• • Standard Linear Rails, to reduce manufacturing time:With lengths in steps of 50 to 100mm. We limit the maximum length to 2 meters for logistic reasons. These rails are delivered:
    • pre-equipped with end stops,
    • undrilled; you will only need to counter-drill them during assembly.
  • IN STOCK Guide Rails in 4 predefined lengths immediately available (stoppers included):
    • 500 mm
    • 1000 mm
    • 1500 mm
    • 2000 mm
  • Specific Guide Rails:

You wish to integrate a rail of a specific length into your project or to receive your rails pre-drilled or with an option? Once again, we have the solution! As a manufacturer, CHAMBRELAN designs for you the ideal sliding rail for your installation, to the millimetre! No more need to cut it in your workshop, we do it for you! A drilling, a lubrication or a specific treatment is necessary? We can do it for you! We invite you to discover our options at the end of this article!

Linear rail with ball bearing runner

2 – Ball bearing or roller runners and load

Once you have chosen the length of your linear guide rail, comes the question of the runner.

The available space and above all the mass of your device will be decisive in the choice of the ball bearing runner. The load we give is indicated PER RUNNER: thus mounting 2 sliders doubles the load capacity. And we have in our range recirculating ball bearing slides that can support 600 kilos per runner!

The load defines the runner which in turns defines the rail!

We manufacture our guides based on 2 technology: Ball bearing runner or roller runner  What are the differences between these two types?

• • Ball bearing runner :

It is the most popular of our range and is perfectly adapted to industrial environments. Strong and compact, these linear rails with recirculating ball bearing runner can support hundreds of kilos, like the E98/G12 ultra-heavy-duty steel linear rail.

Recirculating Ball Bearing Runner

• • Roller runners:

We propose two references of roller skid supporting medium to heavy loads: one full stainless steel guide rail, the other in steel with plastic coated rollers.

These two types of runner can be inserted in several linear guide rails (in steel, aluminium or stainless steel). They slide smoothly and quietly in the rail, more than the recirculating bearing runners. They are appreciated for installations on sliding doors, machine housings or protective hoods. They are adjustable, in so far as the middle runner is on an adjustable excentric screw. This allow to adjust the play and the movment smoothness.

Although a flat mounting is possible and less penalizing than for a telescopic slide, we always recommend an major axis mounting! Indeed, for the same reference, the load can be divided by two depending on the type of mounting:

• •  steel linear guide E46/G52: major axis mounting: 250 kg per runner
  •  steel Linear guide E46/G52: bottom mounted: 125 kg per runner

3-  Material

:

As for our range of telescopic slides, we offer three different materials depending on your project:

Although steel is the most common material, sometimes it is necessary to use stainless steel for outdoor environments or clean rooms. Although steel is the most common material, sometimes it is necessary to use stainless steel for outdoor environments or clean rooms.

5 –  Options :

By following these different steps, you have just determined the standard guide rail that you need to meet your needs! How about going a little further? Indeed, CHAMBRELAN offers several options to help you build your project!

• • Rail drilling:All of our standard linear rails are manufactured and delivered without drilling. Upon request, for an additional price, we can offer bespoke drilling scheme according to your drawing.
    Our runners are threaded. These drillings cannot be modified.
  •  Greasing:the runners are greased in the factory (high pressure bearing grease or white grease). But you can ask for a specific grease:
    • food compatible,
    • high temperature
    • without teflon
    • or even a no greasing (unrecommended).
  • Specific surface treatment of the rail:increased corrosion resistance,
    Additional hardness …
  • wiper kit :for an optimization of the movement of the ball bearing skid, this wiper kit installed on the runner allows to push out of the raceways, impurities and dust.

Do not hesitate to share your projects with us!

CHAMBRELAN offers you the most adapted rail of your project! To help you to identify the right reference do not hesitate to contact us to discuss it!

There is a vast range of linear motion products on the market and it can be difficult to know which product to select. This article discusses the various types of products available according to their rolling element and explores their advantages, disadvantages and limitations. Finally a selection chart clearly lists each product’s characteristics to help with specifying the best linear motion product.

Some of our linear motion products are shown in the table below:

What are Linear Motion Products?

 The primary purpose of linear motion products is to move something from one place to another in one direction along a straight line. Usually this is achieved using a bearing with a rolling element. Traditionally this rolling element would be a ball or roller, but these days some linear motion bearings do not incorporate a rolling element and consequently are known as ‘plain’ bearings. These plain bearings are simply plastic or ceramic bushes and are sometimes lined with PTFE or oil impregnated plastic to help reduce the sliding friction.

It is possible to achieve linear motion without bearings but moving a load without a bearing requires a lot more effort. Using a bearing significantly reduces the friction. For example the coefficient of friction for a recirculating ball bushing can be as low as 0.001 whereas steel against steel (with lubrication) has a coefficient of friction of 0.10.

Linear bearings can be moved in various ways. They can be driven by screws, belts, chains, rack and pinions, or simply pushed by hand.

Linear motion products can be combined together to make multi-directional systems with 2 or 3 axes. Examples are an XY table (2 axes) or a CNC machine (3 axes).

Range of Products

For simplicity, the various linear motion products are discussed according to their type.

Linear Bearings with balls offer the lowest friction. The two main products are recirculating ball bushings and motion guidance systems.

1. Recirculating ball bushings are the traditional linear bearing and are used with hardened and ground shafts. The balls have a very small point contact area which enables very low rolling friction. However the small contact area means that they exert a high force on the shaft and consequently it is essential that they are only used on hardened shafts (e.g. steel shafts Cf53 or stainless steel shafts X90CrMoV18).
2. Motion Guidance Systems (known as ball guides and linear guideways) also use recirculating balls but they run on a profiled rail. The ball groove in these rails is usually gothic arch shaped to maximise the load capacity. Again the rail has to be hardened to prevent the highly loaded balls from deforming it. These systems are typically more tolerant of moments than the traditional recirculating linear bearings.

Roller bearings have a higher basic load rating than equivalent sized ball bearings. However they are less tolerant of lateral forces. Roller bearings are predominantly used as track rollers but they can also be used in cross roller guides.

1. Track Bearings are bearings that roll on their outer diameter along a corresponding track. Usually they contain rollers as their rolling element, but sometimes they may contain balls (usually when radial load capacity is required). Track bearings are very versatile and come in many styles. The simplest is a heavy duty full compliment roller bearing (e.g. NUTR) whilst others have profiled outer rings (v-shaped or concave) to correspond with a shaped, and sometimes hardened, rail. They can be attached using spigots, threaded studs or weldable hubs. Other designs incorporate a secondary axial roller to accommodate lateral loads (e.g. combined roller bearings)
2. Roller guides are similar to ball guides but offer a greater load capacity when compared to the equivalent size ball version. Due to their compactness and precision they are often used in medical applications.
3. Cross roller slides offer very high accuracy and high load capacities. However the nature of their design leaves them vulnerable to contamination and consequently they are predominantly used in clean room or vacuum applications.

Plain bearings (or bushes) have evolved rapidly over the last 20 years with the development of low friction plastics. Plain bearings are typically made from plastic or ceramic. Whilst they offer reduced friction, usually the coefficient of friction is considerably higher than rolling element bearings.

1. Plastic linear bearings are cheap and do offer reduced friction compared to running two similar materials together. Being free of rolling elements there is less worry about product contamination from dirt, dust and debris and there is little noise. Today a wide range of plastics are available offering different advantages.
2. Ceramic linear bearings offer similar attributes to plastic linear bearings. They are quiet and smooth, typically available in the same sizes as traditional recirculating linear bearings and can be lubrication free. Furthermore some allow rotational motion to be combined with linear motion.

Suitability

When selecting linear motion products there are many factors to consider. The range of products available is vast and each product comes in many shapes and sizes. Obviously price is always a factor, but each system has its own advantages and disadvantages and these should be taken into account when designing.

Factors to consider include:

• Load capacity (are any moments involved?)
• Precision (micron precision of miniature ball guide rails to less precise track rollers)
• Support arrangement (fully supported, end supported, cantilevered or telescopic)
• Environment (dirty/dusty, clean room, vacuum, outside…)
• Corrosion resistance (medical, pharmaceutical, food industries)
• Size and scale (compact, heavy duty, or something in between)
• Friction (with regards to the drive system)

Product Selection Chart

Product Friction (µ) * Cost Factor Advantages Disadvantages Ball Bushings
(Linear Bearings) 0.001 to 0.005 Low

•  High accuracy
• Very low friction
• More rigid than plain bearings
• Can carry a small moment
• Long life
• High speed

• Do not like contamination
• Need lubrication
• Must run on hardened shafts
• Some noise

Ball Guides 0.002 to 0.004 Medium (High for Miniature)

• High accuracy
• Carry large moments
• Compact
• Very low friction & start-up friction
• Miniature size option

• Do not like contamination
• Need lubrication
• Rail can be expensive

Track Rolling
Bearings 0.005 to 0.020 Low

• Medium accuracy
• High load capacity
• Tolerant of some contamination
• Can be lubricated for life
• Smooth operation
• Can often support lateral & moment forces
• Low friction

• Lower speeds
• Some of the specialised rails can be expensive
• Higher start up (static friction) than recirculating balls

Cross Roller Slides 0.005 High

• High load capacity
• Very high accuracy
• Compact design
• Low friction

• Expensive
• Do not like contamination
• Rails must be protected with bellows
• Fixed stroke

Roller Linear Guides 0.002 to 0.004 Medium to High

• Higher load capacity than ball guide equivalent
• High accuracy
• Compact Design
• Low friction

• Expensive
• Don’t like contamination
• Not as readily available as Ball Guides

Plastic Bushes 0.1 to 0.4 Low

• High speeds
• Low noise
• Corrosion free (if used with stainless steel shafts)
• Tolerant of dirt
• Shafts can be soft as surface pressure lower
• No lubrication required

• Much higher friction
• Struggle with moment load
• Low accuracy

 

Ceramic Bushes 0.09 to 0.15 Low

• Quiet and smooth
• Linear and rotary motion
• Tolerant of some contamination
• Non-magnetic
• Good chemical resistance
• Wide temperature range
• Can be self lubricating

• Higher friction
• Struggle with moment load

 

 

*Friction varies with loading, surface finish and alignment. Values are for comparison purposes only.

Conclusion

When specifying linear motion products, it is important to consider all the pros and cons of each product. Special attention should be paid to the friction as the coefficient of sliding friction (plain bushes) is markedly higher than that of rolling friction (balls & rollers). The lowest value of friction in the table above is 0.001 whilst the highest is 0.4, a factor of 400 times higher. Clearly the force required to drive the system is considerably higher for plain bushes (and in particular plastic bushes) but that said, they can still serve a purpose in lightweight applications.

For high accuracy applications recirculating ball bushings and ball guides are still the industry leaders. Ball bushings are versatile as they can be used fully supported (open type) or end supported (closed type). Linear ball and roller guides must be fully supported from either above or below. Whilst the roller linear guides offer higher load capacities, recent product development of the ball guides has narrowed the gap between their load capacities. Ball guides continue to be more popular than roller linear guides and consequently the prices tend to be lower.

Where dirt is an issue, the track bearings are clearly the best solution. They offer low coefficients of friction and there are different systems to suit a wide range of loads (e.g. cam followers, V-shaped bearings, combined roller bearings).

The miniature market tends to be fulfilled by recirculating ball bushings & miniature ball guides. Due to their extremely precise nature they are expensive and should only be specified when absolutely necessary.

Corrosion resistance can be achieved with both stainless steel products and specialist coatings. The range of products is limited and the costs can be substantially higher than the standard products. Again, only specify corrosion resistance where it is essential (e.g. food, pharmaceutical and offshore industries).

The correct selection of linear motion products is essential for design longevity. It is important to consider all of the above aspects before choosing the type of rolling element (ball, roller or plain) and then specifying the final product. Whilst cost will always have a major influence, product suitability is key.

Written by Kate Harden (MEng)