If you started to build a machine or a device where you also need linear movement, you quickly come across the question of which linear guide rails would be the most suitable for use. When examining the extremely wide range of guides on the market, where there are many different types of guides, sizes, precision, and different price ranges, the dilemma quickly arises as to which guide rails to choose.
Researching and comparing all possible options can be very time-consuming and complex. To help you with the first steps in choosing linear guides, we have therefore prepared some steps and instructions that can facilitate and speed up the selection process.
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There is a very high probability that someone has already made a machine or device that is very similar to your example. Therefore, it makes a lot of sense to do at least a quick research as a first step and try to get information about the linear guides used in similar machines. The more well-known machine manufacturers are concerned, the more likely it is that their engineers have made detailed analyzes and calculations when choosing the guides and that they have chosen the most optimal guides, also from the point of view of appropriate precision and stiffness of the linear guides. Usually, such guides have also been tested many times in practice.
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Online shopAt the beginning, it is also necessary to make at least a rough assessment of the loads on the guide rails that will occur in your case. The largest or the most critical load usually occurs in the event of an emergency stop or a machine collision. In this case, a very rapid stop occurs, which causes enormous forces on the guides. The moment loads that arise in such a situation are usually the most critical. And that is why it makes sense to make an estimate of the load on the linear guides in such a case.
When you have managed to obtain information about the type of linear guides used in similar machines, it makes sense to check the load capacity of such guides and compare them with your loads. As for the load capacity of linear guides, the most critical part is usually the linear bearing, linear carriage, linear bushing... That is, the moving part of the linear guide assembly. And therefore it is necessary to check the load capacity of this part. Linear bearings and carriages typically have a dynamic load capacity factor C and a static load capacity factor C0 specified in the catalogs. These are the two factors that are used in the formulas for detailed calculations of the life of linear guides. For a first very rough estimate, we can take 10-20% of the value of the dynamic load capacity C, as the load capacity for cases of dynamic movement. If we have an extremely slow movement, we can directly take the entire value of C0 as a very rough estimate of the carrying capacity. The above estimate applies to cases of compressive and tensile loads on the guide and not to moment loads. Linear bearings and carriages tolerate torque loads significantly worse than compression and tension ones. Therefore, it makes the most sense to get rid of them with the correct placement of the guides (2x parallel guide + 4x linear bearing or carriage (2x on each guide)).
With the help of the previous steps, we arrived at the basic selection of linear guide rails and linear blocks using very rough methods. For the final selection or confirmation of the selected guides and linear blocks, it is necessary to calculate the lifetime, which will show whether the selected guides will have the expected lifespan and are therefore suitable for use. In the calculation, other factors such as the type of load, location, speed, vibration, temperature, cleanliness of the working environment… are taken into account in addition to the data on the actual load. Detailed instructions and guidelines for the calculation are given in the manufacturers' catalogs. In our experience, the German linear guide rails manufacturers Bosch-Rexroth provide the best instructions for calculating in their catalogs. However, there are also many online configurators that can help you with the calculation and selection.
Many linear guides are made according to standards or they are produced by different manufacturers with identical key dimensions and very similar characteristics and load capacities, which allows interchangeability between different guideway manufacturers. Of course, every time it is necessary to check and compare all key dimensions, load factors, and if the precision classes are also comparable. At this point, however, a warning applies that in the case of rail guides, the linear carriages and guides must be from the same manufacturer.
From here on, the matter of choice depends mainly on the quality/price ratio. Premium manufacturers such as Bosch-Rexroth, INA, Schneeberger, THK, NSK, HepcoMotion are famous for their high quality and reliability, and have prices accordingly. Very good choices in the middle class are TBI Motion and Hiwin, which have the best ratio between quality and price. Of course, low-priced ECONOMY designs are also available for cases where a favorable price is the main factor.
Installation Procedures & Mounting Verification
The most common arrangement for attaching the rail to a structure is one in which there is not a positive transverse locating surface. The location of the rail under load is maintained by the frictional resistance mounting created primarily by the Rail Mounting Bolt Torque. Therefore, in this instance, proper Bolt Torque is extremely important to maximize the frictional resistance and preclude rail displacement during transverse loading. As a more positive locating method, plates can be installed and dowel pinned in a fashion to more positively resist transverse loading.
There are a number of methods to positively lock the rail and block datum surfaces. These methods will aid in maintaining rigidity and accuracy in applications where vibrations or impacts are present.
RPG Rails are manufactured to be interchangeable, meaning that both edges are datum surfaces. This forgoes having to know which side of the rail is the reference edge. The blocks however have only one datum edge which is the edge with a ground surface.
Push Plates can be used in multiple points along the edge of the rail or block, a single push plate may run the full length.
Push Screws can be utilized to hold the block & rail against the datum surface. Multiple screws should be spaced along the length of the rail or block.
Tapered Gibbs can generate large pressing forces and can cause rail deformity. Therefore, this method should be used with caution.
Needle Roller loading is achieved by the taper of the screw head pressing on the needle roller. The location of the screw is extremely important in order to achieve proper loading on the needle.
RPG Guide Rails are manufactured to be interchangeable, meaning that either side of the rail can be used as a primary locating datum edge. When two or more rails are used in a parallel system, one of the rails is considered the master rail while all others are auxiliary. In a single rail installation there is only a master rail.
Grease Fittings and Accessories.
If block accessories, such as additional end seals and/or metal scrapers are not required, the grease fittings and lube port plugs should be assembled onto the blocks prior to installing the blocks on the rail. However if additional accessories are being used, please refer to the installation instructions on page 35 as some kits will require an alternative lube fitting.
1 - The rail mounting surfaces need to be free of burrs, dirt, rust preventative oil, and foreign material before installation of the rails. Use an oil stone on the master and auxiliary rail mounting surfaces to remove any high spots or dislodge any foreign material that may exist.
2 - Place the Master rail on the prepared rail mounting surface. It is recommended to install the block(s) at a later point in this procedure to avoid accidental block damage. However for applications where subsequent block installation is not possible, proper access to all of the rail mounting bolt holes should be checked and block end accessories installed as applicable.
3 - While holding the rail against the datum edge, insert clean bolts, check for correct bolt fit, and lightly snug all bolts. The torque applied to the bolts during this step should allow for subsequent rail movement as may occur during installation of the push plates.
4 - Install and tighten the clamping mechanisms (Push Plates shown) in sequence starting from the middle of the rail and working towards the ends.
5 - Torque the rail mounting bolts to specification (as shown below) in sequence beginning with the bolts at the center of the rail and working towards each end as shown below. A torque wrench should be used to set the specified Bolt Torque.
6 - The block(s) should now be installed on the master rail only. Be sure the end of the rail is free from burrs and all foreign materials prior to attempting installation. If a datum edge is being utilized on the component that assembles on the block(s), remember to install the block so the ground datum edge of the block faces towards the datum locating surface.
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7 - Install a block and dial indicator on the master rail for alignment purposes. While displacing the block and indicator from one end of the master rail to the other and indicating relative to positive locating feature(s) of the device, verify the alignment of the rail assembly to the indicated locating features
8 - Place the auxiliary rail on the prepared rail mounting surface, insert clean rail mounting bolts, and lightly snug the bolts in preparation for aligning the auxiliary rail to the master rail. Torque the bolts to the same standard as used in Step 3.
9 - Inspect the parallelism and height variation of the auxiliary rail relative to the master rail by using an indicator or other appropriate means. If necessary, the auxiliary rail should be gently re-positioned relative to the master rail within the noted variation limits.
10 - Torque the auxiliary rail mounting bolts to specification in sequence beginning with the bolts at the center of the rail and working towards each end (See Step 5). A torque wrench should be used to set the specified bolt torque. Once the bolts have been sequentially torqued, the alignment of the auxiliary rail to the master rail should be re-verified by using the procedure stated in Step 9.
11 - Install the cap plugs into the bolt hole counter bores as shown below.
12 - Install the remaining blocks on the master and auxiliary rails. Additional end seals and/or scraper kits should be assembled while the block is installed on the rail.
13 - Install the assembled component(s) that mount onto the blocks and lightly tighten the mounting bolts. If push plates are being used, they should be installed and their mounting bolts tightened to secure positive location of the block datum surface to the mating component datum surface.
14 - Sequentially torque the assembled component(s) mounting bolts starting with Block #1 and finishing with Block #4. The linear guidance system should be checked for smooth operation along the entire travel. If any binding or excessive resistance is encountered, the alignments as shown in Step 9 should be re-verified.
15 - As a final measure, the initial charge of lubricant should be introduced into each block as recommended.
Grease Fittings and Accessories.
If block accessories, such as additional end seals and metal scrapers are not required, the grease fittings and lube port plugs should be assembled onto the blocks prior to installing the blocks on the rail. However if additional accessories are being used, please refer to the accessory installation instructions as some kits will require an alternative lube fitting.
1 - The rail mounting surfaces need to be free of burrs, dirt, rust preventative oil, and foreign material before installation of the rails. Use an oil stone on the master and auxiliary rail mounting surfaces to remove any high spots or dislodge any foreign material that may exist.
2 - Place the Master rail on the prepared rail mounting surface. It is recommended to install the block(s) at a later point in this procedure to avoid accidental block damage. However for applications where subsequent block installation is not possible, proper access to all of the rail mounting bolt holes should be checked and block end accessories installed as applicable. Refer to Step 12 for end accessory installation instructions.
3 - Insert clean bolts, check for correct bolt fit, and lightly snug all bolts. The torque applied to the bolts during this step should allow for subsequent rail adjustment as may be necessary during the following alignment procedures.
4 - While keeping the block datum edge in proper orientation, install a block and dial indicator on the master rail for alignment purposes. While displacing the block and indicator from one end of the master rail to the other and indicating relative to positive locating feature(s) of the device, gently re-position the rail into proper alignment. An example of this alignment procedure is shown in Step 7. Reference Step 6 for block installation.
5 - Torque the rail mounting bolts to specification in sequence beginning with the bolts at the center of the rail and working towards each end. A torque wrench should be used to set the specified bolt torque. Once the bolts have been sequentially torqued, the alignment of the master rail should be re-verified by using the procedure stated in Step 4.
6 - Place the auxiliary rail on the prepared rail mounting surface, insert clean rail mounting bolts, and lightly snug the bolts in preparation for aligning the auxiliary rail to the master rail. Torque the bolts to the same standard as used in Step 3.
7 - Inspect the parallelism and height variation of the auxiliary rail relative to the master rail by using an indicator or other appropriate means. If necessary, the auxiliary rail should be gently repositioned relative to the master rail within the noted variation limits.
8 - Torque the auxiliary rail mounting bolts to specification in sequence beginning with the bolts at the center of the rail and working towards each end (Step 5). A torque wrench should be used to set the specified bolt torque. Once the bolts have been sequentially torqued, the alignment of the auxiliary rail relative to the master rail should be re-verified by using the procedure stated in Step 7.
9 - Install the cap plugs into the bolt hole counter bores as shown below.
10 - Install the remaining blocks on the master and auxiliary rails. Additional end seals and/or scraper kits should be assembled while the block is installed on the rail as shown (reference accessory installation instructions).
11 - The assembled components mounting to the blocks should be installed and aligned to the linear guidance system. Once these alignments are completed, the linear guidance system should be checked for smooth operation along the entire travel. If any binding or excessive resistance is encountered, the alignments as shown in Step 7 should be re-verified.
12 - As a final measure, the initial charge of lubricant should be introduced into each block as recommended.
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