Cage rail guide
A cage rail guide (in short: cage guide ) or precision rail guide is a linear guide without rolling element return according to DIN 644 . Since the mentioned DIN only defines the outer dimensions of the guide, these cage rail guides can be made by the respective manufacturers with different rolling elements such. B. balls , cylindrical rollers or needles are equipped. With the appropriate dimensions, rail guides with a special sliding surface ( sliding guides ) are therefore also available from some manufacturers .
Structure and application
Cage rail guides basically consist of a pair of rails provided with mounting holes and the rolling elements arranged between them, which are held in a rolling element cage . These guides can be installed in a horizontal or vertical arrangement, depending on the application. By parallel arrangement of two pairs of rails z. B. - as the animation below shows - the guide for a linear slide can also be implemented.
Version with balls
In the case of cage rail guides with balls, the running surface of the rail can be manufactured so that either two-point or four-point contact occurs between the ball and the running surface. The two illustrations on the right (without the rolling element cage) illustrate this difference, which, depending on the direction of force, has a corresponding effect on the static and dynamic load ratings of these rail guides. While cage rail guides with two-point contact can only absorb forces that act on the balls from the rail direction, guides with four-point contact also enable forces that act laterally on the guide to be absorbed.
- Ball cage rail guides
Cage rail guide with balls
Detail with ball cage
Two-point contact
Four point contact
Version with rollers
In the rolling element cage, from which these guides owe their name, rollers can be held in parallel or in the so-called cross roller arrangement. The roller cages from Ewellix have a special feature with individual cage elements that can be rotated by 90 degrees, which allows the rollers of a cage to be aligned as required. A crossed roller cage can be transformed into a parallel roller cage or vice versa. Technically more interesting, however, is the possibility of being able to set a 2: 1, 3: 2 or, more generally, n: m cross roller arrangement, for example to increase the load rating of the cage rail guide in the main load direction and lower it accordingly in the secondary load direction. With its modular range , this manufacturer also offers the option of using different types of rolling elements with one and the same pair of guide rails.
- Cross roller guides
Cross roller guide
Detail with cross scrolls
Execution with needles
The main difference between the needle and the roller is the relationship between length and diameter . While the length and diameter of the roller are similar, the diameter of needles is relatively small compared to the length. As a result, a crosswise arrangement of needles is not necessary, since this is not technically sensible. Instead, cage rail guides, as well as rail guides with sliding linings on the guide or running surfaces, have a V cross-section. A V-shaped recess is milled and ground in one of the two rails , the other is made as a negative shape with a corresponding V-shaped tip, comparable to a roof .
The needle cage is also V-shaped and has needles on both sides of the V. This cage is then placed between the two different guide rails. If you now turn two needle cage rail guides by 90 degrees - one clockwise, the other counterclockwise - and pair these two rails accordingly, the result is the arrangement shown in the following animation, in which the two Vs open inwards. It is thus possible to build a dovetail guide with the help of two needle cage rail guides .
Hub and cage migration
The stroke of these guides is relatively limited by the length of the rails and rolling elements. A known problem of these guides, which especially at high stroke frequencies emerges is the so-called cage creep (English: cage creeping) seeking to prevent the various manufacturers with appropriate methods. For this purpose z. B. a rack is integrated into the guide rails and a suitable gearwheel is integrated into the rolling element cage , which prevents the cage from migrating because the rack and gearwheel combination imposes a correspondingly defined movement on the cage that is similar to the rack and pinion drive.
Standards for cage rail guides
In the list of DIN standards, the DIN 636 and DIN 644 standards include linear roller bearings, including, according to the DIN definition, not only linear ball bearings , but also
- Profile rail ball guides = profile rail guides with balls as rolling elements as well
- Linear guides without rolling element circulation = count cage rail guides.
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- Author knowledge
- Text in the Wikipedia Commons
