Profile linear guides, made or purchased with your own hands, are roller or ball high-precision rolling bearings that serve in linear movements. They have the ability to perceive forces acting in any direction, excluding the direction of movement.
Types of linear guides
There are two types of linear guides:
- with circulation of balls;
- with roller circulation.
Ball guides make two-, four- and six-row. They are miniature, suitable for use in a limited installation space. Linear guides are made with different drives. Among them, a toothed belt or a ball screw drive (ball screw gears) are more common .
Roller are executed in the form of cylindrical guides and guides with a flat separator.
All guides should have the main properties:
- low friction;
- high efficiency;
- smooth linear movement;
- ability to save operating parameters.
Linear Modules
Recently, in connection with the development of automation, the use of linear displacement modules, which consist of:
- strong bearing profile;
- precise guiding system;
- durable drive mechanism;
- servomotor with simple operation.
Guides with ball bearings and roller bearings find their application in such a modular component. The working drive is carried out using a linear motor, a gear belt or a ball screw mechanism.
Linear tables have also found their application, used when necessary to move large masses along the axes. Due to the dimensions, they perceive large moment loads. In linear tables are used:
- linear displacement bushings;
- ball guides.
Accuracy Measurement Technique
If you make linear guides with your own hands, you need to control the accuracy. This is pretty simple. A rail is placed on the installed base surface. In this case, accuracy is the expression of the average value of the indicator in the central part of the measured surface. The accuracy of linear guides is also determined by measuring the width and length. In this case, the dimensional tolerance for each block that is mounted on the rail is measured.
Rigidity and preload
During operation, the profile rail guides are subject to elastic information due to the applied load. The readings of the strain value depend on the types of rolling elements. But one way or another, it becomes smaller when the load increases.
To increase the rigidity of the system, preload is applied. It reduces the service life of linear guides, causing internal stress in them, but is capable of absorbing deforming loads when the linear guide is operated under conditions of strong vibration or shock load. Due to the fact that the preload causes elastic deformation of the bearings, they become dependent on the negative impact of installation errors. This suggests that more attention should be paid to the precision machining of the mounting surface.
Types of preload:
- normal - used in the presence of minor vibrations;
- light - used in the presence of light vibrations and light torque;
- medium - used for shock loads and strong vibrations, as well as for tipping loads.
Rail Mounting
It is important to know that linear rail guides are subject to force and torque. Values must be determined for them: permissible static moment and load capacity, which are calculated using formulas. When calculating the nominal life of ball and roller guides, it is necessary to use different formulas.
With a constant stroke length and frequency of movements, the resource of work is expressed in time. With compact mounting dimensions, profile rail guides have a high load capacity. Installed in various types of machines or in other equipment, they are mounted in two different ways: in the form of a horizontal rail and in the way of lateral installation.
Since the assembly is carried out from two parallel rails, the location of the first rail is performed on the base side, and the other on the adjustable side.
When working with large shock loads and vibrations, the installation of additional side parts - a side clamping plate, set tightening screws, a conical wedge - helps to eliminate them.
Installation of additional clamping parts when working with light load and low speeds is not necessary.
Linear guides for CNC machines
What is a linear displacement system? This is a combination of gear and linear guides.
Linear guides for CNC are linear bearings, guide bushings, shafts. The guides themselves must solve three main problems:
- be a support for completing the machine;
- with minimal friction, with the necessary accuracy along a given trajectory, ensure the movement of machine parts;
- take the loads that arise during the workflow.
Linear guides are divided according to the method of attachment to the machine. These are guides that provide full support - the method of attachment to the bed along the entire length of the guides, and partial support - the method of end fastening.
Guides with full support have a large carrying capacity, unlike guides with partial support. Sometimes there are options when linear guides are installed along the axes - both with full and partial fixation.
Representatives of this group are linear cylindrical guides. They make it possible to use several types of cylindrical guides:
- polished shaft guides - is the most common (high availability, ease of installation);
- splined shafts - high wear resistance and rigidity, the ability to take torsional forces from the sleeve. It is used at end installation of guides;
- shafts on a support are cylindrical rails. They are used as direct mounting on the machine.
Mounting surface accuracy
Profile rail guides are installed by mounting on a machined base surface. The method of attachment consists in creating a shoulder on the landing surface at the formation of a base surface or carriage along it. Misalignment is possible if there is a groove in the corner of the bead itself.
There is a direct correlation between the accuracy of the rail surface and the accuracy of movement. The accuracy of all equipment will depend on this. At the same time, the accuracy of the machined mounting surface necessarily corresponds to the specified accuracy of movement. It is important to remember that it is necessary to take into account the flatness of the block, excluding the deformation of the carriage.
Base surfaces
To ensure an accurate and simpler installation, it is necessary to create base surfaces that must be located on the carriage and on the rail on one side.
In this case, the mark should be located on the opposite side. If sufficient accuracy is not ensured due to the features of the installation scheme, then base surfaces are also processed from the second side.
Corrosion Protection and Lubrication
To protect the guides from corrosion, they are made of stainless steel. There is an option with applying a special protective coating. Its application is carried out, if necessary, in a high degree of corrosion protection.
Ready-made factory guides are lubricated with grease based on lithium soap. After that, they can be used for their intended purpose. Different working conditions will require the right frequency of adding the same type of grease.