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
Linear guides are of two types:
- with ball circulation;
- with roller circulation.
Ball guides make two-, four- and six-row. They are miniature, suitable for use in limited installation space. Linear guides are manufactured with different drives. Among them, a toothed belt or ball screw drive (ball screw drives) is more common.
Roller are made in the form of cylindrical guides and guides with a flat cage.
All guides must have the main properties:
- low friction;
- high efficiency;
- smooth linear movement;
- ability to maintain operating parameters.
Linear modulesmovement
Recently, due to the development of automation, the use of linear movement modules, which consist of:
- durable bearing profile;
- precise guide system;
- durable drive mechanism;
- servo motor with easy control.
In this modular component, guides with both ball bearings and roller bearings find their application. Working drive is by linear motor, toothed belt or ball screw.
Found their application and linear tables, used when it is necessary to move large masses along the axes. Due to their dimensions, they perceive large moment loads. Linear tables use:
- linear sleeves;
- ball circulating guides.
Method of measuring accuracy
If you make your own linear guides, you need to control the accuracy. This is done quite simply. A rail is placed on the installed base surface. In this case, the accuracy is the expression of the average value of the indicator readings in the central part of the measured surface. Also, the accuracy of linear guides is determined by measuring the width and length. This measures the dimensional tolerance for each block that is installed on the rail.
Rigidity and preload
During operation, profile rail guides are subjected to, due to the applied load,impact of elastic information. Deformation readings depend on the types of rolling elements. But somehow it gets smaller as the load increases.
Preload is applied to increase system stiffness. It reduces the life of linear guides by causing internal stress in them, but is still capable of absorbing deforming loads when the linear guide is operated under severe vibration or shock loading. Due to the fact that preload causes elastic deformation of bearings, they become subject to the negative influence of mounting errors. This suggests that more attention should be paid to the accuracy of the mounting surface.
Types of preload:
- normal - used when there are slight vibrations;
- light - used when there are light vibrations and light torque;
- medium - used for shock loads and strong vibrations, as well as tipping loads.
Installation of rail guides
It is important to know that linear rail systems are subject to force and moment. For them, the values must be determined: the permissible static moment and the load capacity, which are calculated using formulas. When calculating the nominal life of ball and roller guides, you must use different formulas.
With a constant stroke length and frequency of movement, the resource of work is expressed in terms of time. With compact installation dimensions, profile rail guideshave a high load capacity. Installed in various types of machine tools or other equipment, they are mounted in two different ways: in the form of a horizontal rail and in the side mounting method.
Since the assembly is made of two parallel rails, the location of the first rail is on the base side, and the other on the adjustable side.
When working with heavy shock loads and vibrations, the installation of additional side parts - side pressure plate, set tightening screws, conical wedge - helps to eliminate them.
The installation of additional clamping parts when working with a small load and low speeds is not necessary.
Linear guides for CNC machines
What is a linear motion system? It is a combination of transmission and linear guides.
Linear guides for CNC are linear bearings, guide bushings, shafts. The guides themselves must solve three main tasks:
- be the backbone of the machine;
- with minimal friction, with the required accuracy along a given trajectory, to ensure the movement of machine parts;
- accept workloads arising from the workflow.
Linear guides are divided depending on the method of attachment to the machine. These are rails that provide full support - the method of fastening to the bed along the entire length of the rails, and partial support - the end fastening method.
Guideswith full support have a greater load capacity, in contrast to the 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 carry out the possibility of using several types of cylindrical guides:
- polished roller guides - is the most common (high availability, easy to install);
- splined shafts - high wear resistance and rigidity, the ability to accept torsional forces from the sleeve. Used for end mounting rails;
- shafts on the support are cylindrical rails. They are used as a direct attachment to the machine.
Precision mounting surface
Profile rail guides are installed by mounting on a machined base surface. The fastening method consists in creating a shoulder on the seating surface and placing the base surface or carriage along it. Misalignment can be avoided if there is a groove in the corner of the bead itself.
There is a direct relationship between rail surface accuracy and travel accuracy. The accuracy of all equipment will also depend on this. In this case, the accuracy of the machined mounting surface necessarily corresponds to the specified movement accuracy. It is important to remember that it is necessary to take into account the flatness of the block, while excluding deformation.carriages.
Basic surfaces
To ensure accurate and easier installation, it is necessary to create reference surfaces that must be located on the carriage and on the rail on the same side.
In this case, the label should be located on the opposite side. If sufficient accuracy is not ensured due to the peculiarities of the mounting scheme, then the base surfaces are processed on the second side as well.
Corrosion protection and lubrication
To protect the guides from corrosion, they are made of stainless steel. There is an option with a special protective coating. Its application is carried out when a high degree of protection against corrosion is required.
Factory finished slides are lubricated with lithium soap based grease. After that, they can be used for their intended purpose. Different operating conditions will require the correct refill interval of the same type of lubricant.
