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.
Roller guides are made in the form of cylindrical guides and guides with a flat cage.
All guides must have the following properties:
- low friction;
- high efficiency;
- smooth linear movement;
- the ability to maintain operating parameters.
Linear modules
V recent times in connection with the development of automation great importance acquired the use of linear motion modules, which consist of:
- durable bearing profile;
- precise guiding system;
- durable drive mechanism;
- servo motor with simple control.
In this modular component, guides with both ball bearings and roller bearings find their application. The working drive is carried out using a linear motor, a toothed belt or a ball screw mechanism.
Linear tables have also found their application, which are used when it is necessary to move large masses along the axes. Due to their size, they can handle high moment loads. Linear tables use:
- linear bushings;
- guides with circulation of balls.
Accuracy measurement technique
If you are making linear guides with your own hands, you need to control the accuracy. This is done quite simply. A rail is placed on the installed base surface. In this case, accuracy is an 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, the profile rail guides are subjected to elastic information due to the applied load. The deformation readings depend on the types of rolling elements. But one way or another, it becomes smaller when the load increases.
A preload is applied to increase the rigidity of the system. It reduces the service life of linear guides, causing internal stress in them, but at the same time is capable of absorbing deforming loads when the linear guide is operated under severe vibration or shock loading. Due to the fact that the preload causes elastic deformation of the bearings, they become dependent on negative impact installation errors. This suggests that more attention should be paid to the accuracy of the machining of the mounting surface.
Preload types:
- 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.
Installation of rail guides
It is important to know that linear rail guides are subject to force and moment. For them, values must be determined: permissible static moment and load capacity, which are calculated using formulas. When calculating the nominal life of ball and roller guides, different formulas must be used.
With a constant stroke length and frequency of movements, the work resource is expressed in terms of time. With their compact installation dimensions, the profile rail guides have a high load capacity. Installed in different types machines or other equipment, they are mounted by two different ways: horizontal rail and side-mounted.
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 pressure plate, set tightening screws, a tapered wedge - helps to eliminate them.
The installation of additional clamping parts when working with a low load and low travel speeds is not necessary.
Linear guides for CNC machines
What makes up 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:
- to be a support for completing the machine;
- with minimal friction, with the required accuracy along a given trajectory, ensure the movement of machine parts;
- take the loads arising from the work process.
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 attachment.
Fully supported rails have a higher load capacity than partially supported rails. 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 guide shafts - 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 for the end mounting of the guides;
- supported shafts are cylindrical rails. They are used in the form of direct attachment to the machine.
Precision mounting surface
The profile rail guides are mounted by fastening to the machined base surface. The fastening method consists in creating a collar on the landing surface and establishing along it base surface or carriages. Elimination of distortions is possible if there is a groove in the corner of the shoulder itself.
There is a direct relationship between rail surface accuracy and travel accuracy. The accuracy of all equipment will depend on this. In this case, the accuracy of the machined mounting surface necessarily corresponds to the specified travel accuracy. It is important to remember that it is imperative to take into account the flatness of the block, while excluding deformation of the carriage.
Base surfaces
To ensure accurate and more easy installation, you need to create datum surfaces that should be on the carriage and on the rail on one 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 installation scheme, then the base surfaces are processed from the second side.
Corrosion protection and lubrication
To protect the guides from the effects of corrosion, they are made from There is an option with the application of a special protective coating... Its application is carried out when necessary in a high degree of protection against corrosion.
Factory-assembled rails are lubricated with lithium soap grease. After that, they can be used for their intended purpose. Different operating conditions will require replenishment of the same type of grease as needed.
Modern processing of materials and the manufacture of complex parts requires the use of high-precision machine tools. High-precision equipment means that the parts from which it is made are also high-tech and accurate. And each type of machine has its own requirements for these parts.
To achieve the required processing accuracy of a whole batch of products, it is necessary to ensure that all necessary operations and their repeated error-free repetition. This task is successfully performed by computer numerical control (CNC) machines.
The movement of the workpiece, the processing tool and related elements of the machine structure provides guides.
Device
The most general description guide: it is a unit that ensures the movement of the workpiece, tool and related elements along the desired path with a given accuracy.
Main parts guide — robust shaft or profile guide and movable units moving along them carrying the working elements of the machine.
Constructive decisions guide, as well as ensuring movement along it is very varied and are subordinated to the implementation of specific tasks of metalworking.
Hiwin profile rail device
Work principles
The guides of the CNC machine are fixed to such an extent reliably that even their minimal shifts during the operation of the equipment are excluded - under the influence of weight, movement or vibration of the working units.
In the process of processing workpieces along the guides, under the control of a given program, the functional units of the machine are easily moved and firmly fixed, ensuring the performance of the necessary working operations.
Used, depending on the method of moving the movable unit, the guides sliding, rolling and combined which combine both rolling and sliding movement.
Slide guides, in which the surface of the shaft is in direct contact with the sleeve moving along it, are subject to the action of significant frictional forces, which in the process of work change significantly in direction and force. Frictional load will wear out the guides. In addition, the difference between the frictional force at rest and the frictional force during movement greatly affects the operation of the sliding guides.
At low speeds, due to this difference, the movement of the working units occurs in an abrupt manner - this is unacceptable for CNC machines.
To reduce the influence of friction forces, anti-friction plastic linings are used, as well as a number of other ways to reduce these forces. Depending on how friction is reduced, slide guides are subdivided into hydrostatic, hydrodynamic and aerostatic.
V hydrostatic liquid (oil) lubrication is present at any sliding speed, respectively, the uniformity of movement and its high accuracy are ensured.
These guides have two problematic points: difficult arranged system lubrication, as well as the need for special locking devices to secure the displaced unit in the desired position.
The hydrostatic guides are equipped with special oil pockets, into which the lubricant is supplied under pressure and flows out, creating an oil layer along the entire length of the contact surfaces. The layer thickness is adjustable.
Hydrodynamic effectively reduce friction due to the "floating" of the moving unit in the oil filling the gaps between the lubrication grooves on the working surfaces of the guides when moving the units along them.
Hydrodynamic guides work well only at significant sliding speeds.
The problematic moments are acceleration, as well as braking of the moving part.
Aerodynamic work on an air cushion.
Structurally, they are similar to hydrostatic ones, they have pockets into which air is supplied under pressure.
Compared to oil, air bag withstands less weight and dampens shocks and vibrations worse.
The air supply paths, as well as the gap between the surfaces to be divided, are easily clogged.
At the same time, in contrast to hydrostatic guides, aerostatic guides do not need additional fixation: immediately after the air supply is stopped, the moving part sits tightly on the shaft.
Rolling guides, in accordance with the shape of the bearings, there are ball and roller. With comparable dimensions, roller bearings can withstand a greater load. Structurally, they consist of a set of "rail-carriage", "linear bearing-shaft", "rail-rail with a flat cage".
Such guides have reduced friction indicators, provide accurate movement and stop in the desired position, at low speeds, movement along them does not lose smoothness. Lubrication of the rolling guides is also straightforward.
At the same time, they are more expensive, less shock absorbing and more sensitive than slideways to contamination.
Combined guides combine sliding on one side with sliding on the other. This type of guide is the most widespread and combines both the advantages and disadvantages of rolling and sliding guides.
Classification, areas of application, advantages and disadvantages
The shape of the bearing shaft of the guides can be linear and circular; they are placed horizontally, vertically and obliquely. The guides are fastened either along the entire length, or only at the end sections.
Linear guides are subdivided according to the shaft profile
Cylindrical rails ( polished shaft). The sectional shape is a circle. Polished shaft is the most budgetary and widespread guide, easy to handle and install: only the ends are fixed. The surface of such a shaft is hardened, its smoothness is almost perfect, the movement of the bearing couplings on this surface occurs with very little friction.
However, where the advantages are, the disadvantages are also rooted: the ease of fastening is, at the same time, the lack of a rigid connection with the desktop and sagging in the case of considerable length and / or load.
The set "ball bearing-polished shaft" has a low price. In this case, for movable bushings low carrying capacity... As a rule, there is backlash, which increases with use. Service life under normal temperature conditions is 10,000 hours, but when the working area heats up, it is significantly reduced.
It has profiled straight grooves, grooves, raceways, along the entire length, designed for additional fastening of the bushings moving along the shaft with the working units of the machine. At the same time, the backlash, in comparison with the polished shaft, is significantly reduced and, due to the more complex manufacturing technology, the price of such guides increases.
Guides with flat by rails rectangular section, as a rule, are profiled with splines for the applied rolling elements.
So, ball profile guides provide precision movement valid straightforwardness, carrying capacity... They have low backlash... They wear-resistant. They are used for completing robotic lines, in metal-cutting machines and precision metalworking
At the same time, it is rather difficult to install such rails; high requirements for straightness and roughness. In terms of cost, due to the complexity of production, they are much less affordable than polished shafts.
Roller profile guides have flat raceways. Rollers are installed in the support modules. Even more load-bearing, stiffer and more durable than ball splines. Used in heavy duty milling machines.
Prismatic dovetail guide
Prismatic guides with triangular rails and guides "dovetail" with a trapezoidal section are used where needed high rigidity joints, for example, in metal-cutting machines.
In particular, dovetail guides are carried out with the bed as one whole. Manufacturing, as well as repair " dovetail"- complex procedures that require a lot of labor. However, they provide high-precision movement of moving elements.
Specifications
Due to their design, the guides provide only one degree of freedom when moving the movable unit along them.
According to the "type of activity" they must have high strength and durability.
That's why basic materials for making them support parts(shafts and rails) are:
gray cast iron... It is used in the manufacture of guides that are integral with the bed.
Steel. It is used for the manufacture of removable overhead guides. They use hardened steels with high hardness (60-64HRC), for example, grade 40X with high-frequency current hardening.
The production of guides provides for such a length that provides full coverage of the bed or build-up to the required dimensions.
Accuracy standards in the manufacture guides are standardized and constitute 0.02mm permissible deviation with a length of 1 meter.
The permissible surface roughness and dimensions according to the workload.
In particular, on small machines with a working field of 30x40 cm, the diameter of the guides should be 2.5 cm.
The area of the working field and the hardness of the material to be processed also determine the required class of guides. So, with a working area of over 0.7 m 2 with the processing of steel blanks, only profile rails are required. More a budget option a polished shaft is unsuitable in this case.
For each specific area of work, according to the developed algorithms, a calculation is carried out that determines the best option parameters of the guides of the machine.
To reduce the coefficient of friction, sliding pairs "metal-plastic" are used, and the plastic attachments are fluoroplastic, Teflon, torsite and similar materials.
To ensure smooth movement of hydrostatic and combined guides, specialized "anti-sway" oils are used.
Installation
Correct and accurate installation of the guides of the CNC machine is the key to its trouble-free operation.
Therefore, before starting this operation, remove all contaminants from the edges and the plane of the base mounting surface, which should have a strictly horizontal, level-verified location.
Consider installation of a double-rail guide.
Select, according to the markings on it, the main rail.
If the base rail is attached to the side edge of the base surface, it is carefully placed on the supporting surface and temporarily bolted in a position slightly pressed against the side edge.
In this case, the mark on the rail is aligned with the lateral base surface of the support. The mounting holes of the rail must not be offset from the base holes.
Then the screws holding the rail are tightened in order so that the rail is firmly pressed against the side bearing surface.
This eliminates the displacement in the horizontal plane.
Then tighten the set bolts (vertical) in order from the middle to the ends of the rail. In this case, the required tightening torque is determined with a torque wrench.
If the main rail has no clamping screws that provide lateral fastening, it is installed using a vice.
The fixing bolts are tightened temporarily, and then, pressing the rail with a small vice against the base side edge where the set bolts are located, fully tighten these bolts to the prescribed torque, moving from one end of the rail to the other.
In that case, if there is no reference edge on the side of the main rail, its alignment in the horizontal plane is carried out using a sighting level, a digital indicator or a straightedge.
After correct installation main rail, an auxiliary rail is installed parallel to it.
In this case, use straightedge... It is placed parallel to the main guide; parallelism is determined by a digital indicator. After parallelism has been achieved, the bolts of the auxiliary rail are finally secured.
In addition, special ruler guides as well as aligning the position of the auxiliary rail using carriages from the set of rail guides.
To install the carriages, a table is placed on them and temporarily fixed with working bolts. Then the carriages are pressed from the side of the main rail to the side base surface of the table with fixing bolts and the table is installed. Then the set bolts on the main and sub side are fully tightened.
If the carriages are used for correct installation auxiliary rail on the main rail, then the table is placed on the carriages of the main rail, and the auxiliary rail is temporarily fixed.
The installation bolts of the two carriages on the main rail and one of the two carriages on the secondary rail are fully tightened.
The bolts on the auxiliary rail are then fully tightened in order while temporarily securing the second carriage to the auxiliary rail.
In this case, the main rail serves as a reference point, and the table with carriages - a parallelism indicator.
For processing large workpieces guides are extended to the required length by connecting several sections... Supplier companies specifically stipulate this possibility.
Butt joint sections are marked in such a way as to ensure consistent installation. In this case, the installation bolts are located closer to the ends of the sections to be connected.
The sections must be supported along their entire length.... Therefore, it may be necessary to build up the bed itself.
The build-up sections are carried out through the same installation procedures as the main ones.
Machining is one of the most detailed and diversely equipped manufacturing industries. A wide range of accessories is available for programmable machine tools.
Correct selection of the optimal constructive solution and the adjusted installation of the guides of the CNC machine is a reliable guarantee of the quality of metalworking on this machine.
This article will consider the types of guides for a CNC machine, their main features and advantages.
POLISHED GUIDE SHAFTS
The most common and budgetary type of guides. Differs in low cost, ease of processing and installation.
They are made of high-alloy steels, as a rule, structural bearing steels, and undergo induction hardening of the surface with subsequent grinding.
This results in longer run times and less shaft wear.
Ground shafts have perfect surface and provide movement with very little friction.
The shafts are attached only at 2 points at the ends, and therefore their installation is not particularly difficult.
However, many unscrupulous manufacturers often make shafts from cheap and soft varieties high-carbon steels, taking advantage of the fact that the buyer does not always have the means to check the type of material and its hardness.
The disadvantages of polished shafts include:
1. Lack of attachment to the bed.
The shaft is attached at two points at the ends - this makes it easier to install the guides, but it leads to the fact that the guides are installed independently of the working surface of the table. At the same time in gantry machines it is highly desirable to put the guides in a rigid connection with the table. Such a connection reduces processing errors, if the desktop was subjected to curvature, "turned with a screw" - the guides, repeating the bends of the table, level out part of the error.
Shaft fixing
2. Long sagging.
In practice, due to sagging, shafts are used no more than 1 meter in length. In addition, the ratio of the shaft diameter to its length is important - to obtain acceptable results, its value should be at least 0.05, preferably within the range of 0.06-0.1. More accurate data can be obtained by simulating the load on the shaft in CAD packages.
Types of linear bearings on the shaft:
1. Linear bushings
Linear rolling bearings have large backlash compared to rail carriages and lower load characteristics.
In addition, to protect the carriage against rotation, it is necessary to use at least two guide shafts per one axis. Disadvantages of linear rolling bearings:
- Low lifting capacity.
- Corollary of the previous point, as well as the structural structure of linear bearings.
- Fragility.
- Each ball of a linear bearing touches the shaft at one point, which creates a very high pressure... Over time, the balls can roll a groove on the shaft, after which the shaft must be replaced.
Ball bushings
- Backlash
- Low-cost linear bearings by many manufacturers are often manufactured with a very significant backlash.
- Sufficiently sensitive to dust and shavings on the shaft
2. Linear plain bearings
Sliding bushings use sliding friction and are made of bronze, brass, caprolon and other materials.
With proper tolerances, the bronze plain bearing offers the same accuracy and load capacity as a rolling bearing, while also carrying dust and chips more easily. However, you need to make sure that you can always get the bearing material and process it properly.
In addition, periodically, as wears out, the sleeve bearing has to be adjusted to eliminate gaps. In most cases, Linear Bushings are preferred for beginners due to their high availability and interchangeability.
SPLINE SHAFT (BALL SPLINE)
Splined shafts have special raceways for bushing balls. They are more wear-resistant and stiffer than conventional shafts and can also take torsional forces from the bushing.
Combining the advantages of shaft mounting, the wear resistance of profile rails with the possibility of creating an interference fit, splined shafts are used where it is required to mount guides exclusively at the ends.
However, due to their significantly higher cost (compared to polished shafts), they are rarely used in the construction of conventional machine tools.
SHAFTS ON A SUPPORT
Profile rails are complex and expensive to manufacture, so there are fewer rail manufacturers than shaft manufacturers. They, as a rule, value their reputation, because the quality of profile rails is much more stable.
ROLLER PROFILE RAIL GUIDES
Roller rails are a subspecies of profile guides, in which the raceways are flat, and instead of balls, rollers are used in the support modules.
This made it possible to increase the rigidity of the guide rail, load capacity and durability.
Roller guides are used in high-load CNC metalworking machines designed for milling ferrous metals, steel, stone.
It is unlikely that you are looking for just such guides, otherwise you would not have read this article.
GUIDES "LASTOCHKIN TAIL"
AND PRISMATIC GUIDES
This type of guide is used where very high rigidity is required, for example, in industrial metalworking machines. - low rigidity and load capacity, limited accuracy, the need for periodic adjustment, low price, low availability finished products on the market. Shaft sags at great length.
Roller profile guide
- Shaft and Linear Bushing- low rigidity and load capacity, limited accuracy, average cost... Shaft sags at great length. Used in hobby and middle class machines.
- Supported Shaft and Linear Bushing- average stiffness and carrying capacity, limited accuracy, average cost. The rail repeats the deformations of the bed, eliminating the error. Used in hobby and middle class machines.
- Profile guides- high rigidity, accuracy, wear resistance, high carrying capacity, no adjustment required, high cost. An important factor is the complexity of the installation of profile guides and the need for appropriate preparation of the mounting surfaces. Used in medium and industrial grade machines.
If you have read everything, but the situation has not become clearer, in conclusion, a few specific recommendations:
- If you plan to mill metals or stone on the machine, there is no alternative to profile rails.
- If your machine will have a working area of more than 0.7 sq. m, it is also best to use profile guides.
- If your machine has a working area smaller than A4 format, it is planned to process soft materials- shafts with a diameter of 16–25 mm are suitable.
- If you still find it difficult to choose, please contact our specialists for advice.
Cylindrical guides are used in CNC machines, for which machining accuracy is not so important, and the cost of equipment is put in the first place. Induction surface hardening technology (hardness up to 60 HRC) increases wear resistance, subsequent grinding to Ra 0.8 max reduces the coefficient of friction. They are used in a set with both bronze or fluoroplastic sleeve bushings, and with rolling bearings.
Polished shafts
They are characterized by affordability and ease of installation, which reduces repair costs. They are not recommended for use as guides for movable tables, the flow rate of which exceeds 1 m, since fastening to the bed at two points leads to sagging under load. At the same time, they are suitable for moving the spindle along the Z axis, provided that the spindle is not loaded (engraving, cutting thin sheet metal, woodcarving, etc.) and counterbalanced by a counterweight.
Disadvantages:
- when using rolling bearings, the pressure from the ball is applied at one point, over time, the groove is pressed at this point;
- hypersensitivity to chips and dust;
- impossibility of fitting the bearing to the shaft and creating a preload.
Nevertheless, these disadvantages are offset by the low cost and ease of shaft replacement, and the problem of dust and shavings in wood and stone processing workshops is solved by installing a socket hood directly in the working area.
Cylindrical rails on supports
The main disadvantage of a polished shaft is the lack of support along the length, in this design it is compensated by the fact that the shaft is laid on aluminum profile, attached directly to the bed. The resistance to bending load is the same at all points along the shaft length, so the cylindrical rail does not bend.
Used when building budget machines with working area more than 1 m. But there is one nuance due to the design of the bearings. An open bearing contour perceives forces applied in different directions in different ways, which requires control of the coincidence of the center of mass of the workpiece placed on the table and the geometric center of the table. For the same reason, they are not used in the kinematic diagrams of the Z axes in machines with heavy spindles.
Cylindrical guides are a budget option ideal for use on small or lightweight machine tools with light spindles.
The mechanical processing of any material means, first of all, precision and productivity. Regardless of the type and purpose of the machine, there are basic elements, the parameters of which cannot be neglected. The basic component for a metal cutting, woodworking or processing device designed for plastic are guides that ensure the error-free and cyclical processing.
What are the guides
Any machine is based on the machining precision provided by the guide rods. You have to make working units with your own hands, but there are those that you can't do yourself, only factory-made parts are suitable.
For example, a working body milling machine it is hardly possible to make, as with a drilling or. Therefore, you have to use ready-made solutions- drills, drives, engravers or electric jigsaws... With the guides, the situation is simpler, since their characteristics and appearance directly depend on the purpose of the unit.
Almost all of them are used in factory and homemade constructions there are only two types - sliding and rolling. According to the principle of bearings, their method of operation is clear - some are based on sliding, while others use rolling bearings in their design. 
For equipment low power and do not require precision and productivity, they use the sliding principle. Basically, such parts are used by bench-top drilling and turning units, as well as woodworking ones. There are also subspecies, but consider those that are easiest to make with your own hands from what is on sale.
Guides for CNC machine
CNC machining centers for small batch and home use- an expensive thing and not everyone can afford to buy a format boring or CNC machine, but you can easily make a device that is tolerable in terms of processing quality and cleanliness of cut with your own hands. Let's look at a few designs, but first let's look at the factory-made parts to understand the basic principles of operation.
All guides for programmable machines are circular or linear, it depends on the path along which the movable unit moves in coordinates. We will consider only linear ones, as the most demanded by DIYers, and there is no special need for the use of circular devices.
The easiest option for homemade programmable devices of any type is sliding parts. Their parameters change depending on the performance requirements. Basically, cylindrical rods are used, they are pre-grinded, bronze bushings move along them. The support is made without bushings, but this, of course, will affect both the resource of the rods and the accuracy of processing the workpieces.
As rods on a surface grinding emery, drilling or simple turning, galvanized pipes of different diameters can be used. It is good because it is cheap, easy to process and shape, but there are also significant disadvantages:
Nevertheless, in many low-power devices they are used and if the accuracy drops, the pipe is simply replaced with a new one. They are more ingenious when making a small router based on sliding devices from old dot matrix printers. This option has shown itself in practice positively and they will work in them for more than one year. We have presented several of these designs in the photo. There is also another good option to get by with a little blood when building firmware.
CNC machines made of furniture rods
An excellent option when you need to achieve thoroughness of processing, especially in woodworking machines for the production of furniture in small batches, in belt-grinding, milling machines based on a ready-made milling cutter of low power. Furniture parts are inexpensive, although their resource is less than that of similar sliding elements from printers or typewriters.
An example of using furniture rods on a format boring machine is shown in the photo. It is clear that the dimensions of the bed and movable table are adjusted depending on the purpose. However, if you use ball-type furniture on a drilling machine, they will not be demolished, since the load and frequency at work with a milling cutter or drilling machine are significantly different from the loads on a panel saw.
There is always a way out, and according to the examples given, it is quite possible to choose slide guides for your CNC machine with the desired parameters. Good luck with your work!