This article presents theoretical considerations in the pre-creation phase. Without this knowledge, you should not start creating it, so the article is recommended for reading for those who are just planning to build their own CNC machine. A year and a half after its publication, I wrote the following article for those who already have the machine itself. It is called . In it, I will talk about the methodology for measuring accuracy and the conclusions that follow after measurements.
Let me start by saying that for home production CNC machine is simply irreplaceable equipment. Therefore, I decided to assemble a CNC milling machine with my own hands. This is not an easy task and, I must say, extremely costly. On this moment the amount spent on the creation of the machine is already approaching the cost of the finished machine. But for me it was not a secret - they write about it everywhere and often. It’s just that when you make a CNC milling machine with your own hands, you will inevitably know all the subtleties thoroughly: how it works, how to set it up, what steps to take to increase its accuracy, processing speed and other parameters. In general, you plunge headlong into the technological environment of machine tool building.
In this article on the Dimanjy TechnoBlog, we will talk about the accuracy of a CNC machine, depending on the choice of transmission type, stepper motors and their modes of operation.
Quite a bit of theory. If you have already been interested in CNC milling machines, then you probably know that they consist of a cutting / milling tool (spindle with a cutter installed) and a linear tool movement system, i.e. a system that provides automatic movement of the tool in space. That's how the CNC machine myself cuts the specified part.
The system of linear movements of the machine is built (usually) on the basis of stepper motors. Here I will be looking at DIY CNC machines, and not expensive industrial designs that can be powered by much more expensive industrial servo motors. And when assembling a machine with their own hands, they usually try to stick to a minimum budget. Exactly budget option is the use of stepper motors.
We go further. The task of a linear motion system based on stepper motors is to convert rotary motion the motor rotor into the translational (linear) movement of the carriage to which the tool is attached. There are two types of converters: screw-nut transmission (and its varieties) and gears (timing belts or racks).
Choosing the type of transmission (screw or gear), the designer is guided by the tasks that the machine faces, the requirements for accuracy and the availability of certain materials. In general, a screw drive provides a higher resolution of the machine tool than a gear drive, but is inferior to the latter in tool movement speed. If you need a machine capable of milling jewelry, then it should most likely be built on helical gears, but it will be slow. If you want to cut a lot and quickly do not small parts(relative to jewelry), then it is desirable to build it on gears. But it will not be possible to do something very small on it, because. its resolution will not allow. Let's now take a look at specific examples.
The calculations start with a stepper motor, which has a parameter such as the number of steps per full revolution. For homemade CNC machines, stepper motors are usually used, having 200 steps per revolution (360 ° / 200 \u003d 1.8 °). Stepper motors can operate in half step mode and take 400 steps per revolution. Now let's try to shift this number to the screw and gear train, and see what theoretical resolution can be achieved from them using the same stepper motor. Hereinafter, I will talk specifically about resolution, and not about accuracy, although people often confuse these concepts and by “accuracy of a CNC machine” they mean exactly its resolution.
So how much resolution can you get on a screw drive with a stepper motor with 400 half steps per revolution? The screw gear has such a parameter as the thread pitch. Let the thread pitch of the screw gear be 2 mm (this is the pitch that is done on ordinary building studs). Those. a nut screwed onto this screw will move 2 mm per full turn. If you attach a stepper motor to the screw and turn the screw with it, it turns out that in one half step of the motor the screw will move the nut by 2mm / 400 = 0.005 mm! or 5 microns! Incredible! With such permission, the Tula Lefty would not only shoe a flea, but also fill it with a tattoo!
However, imagine now that with such a screw drive we need to move the tool 20 cm. This is 100 turns of the screw or 100 x 400 = 40,000 half steps. Stepper motor speeds are usually relatively slow - 50 rpm is fast enough for a stepper. This means that in order to move the tool by 20 cm, making 100 revolutions, you have to wait as much as 2 minutes! Catastrophe!
Let's now look at the accuracy of the toothed belt. More precisely, the resolution that can be achieved using a gear on a toothed belt. In homemade CNC machines, timing belts with a tooth pitch of 5.08 mm are often used. A pulley is put on the rotor of a stepper motor, which also has a certain number of teeth engaged with a toothed belt. For example, let's take a 12 tooth pulley. It turns out that for a full revolution of the stepper motor (400 half steps), the toothed belt will travel 12 x 5.08 = 61 mm. This means that one half step accounts for 61/400 = 0.15 mm.
Yeah! It doesn’t smell like microns here, and we don’t even fit into the “ten” (one tenth of a millimeter). But ask yourself the question, will you create parts in which features (for example, adjacent holes) will be located closer to each other than 1 mm? And now imagine how fast your CNC tool will move: at 50 rpm, the toothed belt drive will move the tool 61 x 50 = 3000 mm or 3 meters! in a minute. This is not 10 cm per minute on a screw gear!
Here you could object to me, especially if you are studying the issue of creating CNC machines with your own hands enough long time, because there are craftsmen on the network who accelerate stepper motors to cosmic speeds. I met references to almost 500 rpm! With this speed, you can turn the screw gear quickly enough. Theoretically, yes ... But in practice, a stepper motor loses its torque very much with an increase in rotational speed. It is not designed to spin fast at all - there are other types of motors for this.
From the very beginning, when I just started making a CNC machine with my own hands and began to describe this process in my Dimanjy Tech Blog, I also decided to use a screw drive. I collected 100 rubles each for construction studs in the nearest store, ordered caprolon nuts for them, bought bearings at the market, machined holders for them ... But when I assembled all this economy into a single structure, I simply could not turn the transmission screw with my hands! Construction studs are all curved - they give a runout of up to 2 mm per 1 meter of length. It is simply unrealistic to center bearings at home, so there could be no question of any alignment. The question is, how will all this rotate a poor stepper motor? But no way!
After the first unsuccessful experiment, I decided to pay attention to the industrial gear elements for machine tools. Began to compare them and estimate the cost.
A screw drive requires high precision screws, bearings for each screw on both sides, bearing holders and a gear nut for each screw. But the screws need to be rotated somehow, so stepper motors also need special couplings, and even better - the same toothed belts and two pulleys: one for the motor, one for the lead screw. In general - a lot of details, and even a big headache when setting up, not to mention initially increased requirements to the frame of the future machine to maintain alignment when installing screw holders. A double price tag with a deliberately unpredictable result. Nafik-nafik!
Transmission on a toothed belt turned out to be the most budget option. For a homemade CNC machine, you only need the timing belt itself, pulleys for it on stepper motors and two tension rollers per pulley. I made tension rollers from ordinary bearings. Adjusting the toothed belt comes down only to its tightness - just so that it does not hang out.
So it's decided — I'm doing it on a toothed belt. I bought components, remade the frame, installed stepper motors and belts. And voila - everything rustled, and quite cheerfully! The engines did not experience any difficulties when moving a multi-kilogram bed along with a heavy spindle. All assembly defects and small curvature are smoothed out by the toothed belt transmission due to its own elasticity. However, the low resolution of 0.15 mm did not give me peace of mind. Of course, you always want more accuracy, and I started looking for ways to increase it.
The first thing that comes to mind is to use a reducer. But this leads to a complication of the design, its rise in price and, again, a decrease in speed! Is it possible to somehow increase the resolution of a homemade CNC machine while maintaining the same speed of movement? It turned out that this is theoretically possible. The solution was found in the way to control the stepper motor.
The thing is that a stepper motor can work not only in full-step or half-step mode. By controlling the current in the motor windings in a special way, it is possible to achieve the so-called “microstepping” mode of operation of the motor. At the same time, it is possible to split one full step into many smaller steps, getting 1/4, 1/8, 1/16, 1/32 steps and even more! Already at 1/4 step, the resolution of the CNC machine on a belt drive increases by 2 times from 0.15 to 0.075 mm, at 1/8 - up to 0.04 mm, at 1/16 - up to 0.02 mm. This is already something!
However, there is a small problem here. The fact is that manufacturers do not guarantee the operation of the engine in microstepping mode. In addition, different stepper motors behave differently in microstepping mode, and nowhere is the characteristic of a particular motor in microstepping mode described. It is understandable - this mode, in principle, was not provided for when developing a stepper motor, which in fact is a finite automaton with well-defined states inherent in digital technology(1 - stepped, 0 - standing still). Microstepping is an attempt at analog motor control, originally designed for a "digital" signal.
In microstepping mode, a stepper motor reveals to us all its analog non-linearity, which is inherent in everything that exists in our world. If the current in one of the windings is fixed, and in the second it is smoothly raised from zero to the same level, then the motor rotor, contrary to expectations, will not move smoothly. When the current in the second winding is about 50% of the current in the first, the stepper motor does not move at all. From 50 to 70%, the rotor comes to life and begins to turn barely noticeably, and from 70 to 100% it turns three times faster. Those. the dependence of the angle of rotation on the magnitude of the current in the winding is close to exponential. This picture is typical for powerful hybrid stepper motors used in homemade CNC machines. If we take a low-power stepper motor from an old printer, then the dependence there is already different, almost linear. And so for each engine. Different motors - different characteristics for microstepping.
There are many stepper motor controllers on the market that support microstepping, but they use a regular sine table to implement it, which does not take into account nonlinearity and individual characteristics each specific engine. What is the use of such a crooked microstep? Oddly enough, but there is even a use for this. The point is that in normal full step or half step stepper motors vibrate a lot. Mechanical resonance sets in, which causes the entire machine to vibrate and rumble, which can have an extremely negative effect on accuracy. If, however, each step coming from the control program is divided into microsteps and fed to the engine, then the movement will become much smoother and quieter. But such controllers do not provide fixation of the motor in the microstepping position, because the position of the rotor in this intermediate state is completely unpredictable for a conventional microstepping controller.
Let's now imagine that the controller knows from somewhere about the non-linearity of the stepper motor characteristic, and instead of the standard sine table stored in its memory, it will select values for the winding currents from a special individual table compiled for a specific motor. Then the microstepping mode can be used not only to reduce resonance, but also to really increase the resolution of the CNC machine!
But how to transfer this magic table, calculated individually for each motor, to the stepper motor controller? Pre-calibration of the stepper motor and a special controller that supports this calibration table will help us solve this problem! This is what I'm currently developing. On my Dimanjy Tech Blog you can follow its development progress and latest updates.
I decided to do it optically using a conventional laser pointer rigidly mounted on the rotor of a stepper motor, but read about it in my next article on the Dimanjy Tech Blog.
I am also starting a series of articles on how to create , because I already have some results in this direction. Stay tuned!
On this complex equipment, all kinds of parts are made of metal, plexiglass, acrylic or plastic, wood. Their versatility lies in the fact that they are well suited for cross planing, the formation of the most complex surfaces, in particular, curvilinear ones; carry out selections of the crest, tongue, folds, groove, slots and moldings.
Description of the machine
The standard equipment of the machine includes:
- heavy and powerful base;
- Desktop;
- , with the simultaneous presence of the spindle shaft;
- a set of several tools for cutting materials;
- front disc brake.
The design of machine tools today includes many important devices that ensure the accuracy of processing and ease of use. It is important to know about them so that the choice of a CNC milling machine is meaningful and correct.
Don't forget the spindle!
One of important qualities in the operation of the spindle shaft electric motor - the ability to rotate it smoothly and evenly. When assembling, bearings of the highest (accuracy class) are selected, and the collet must have increased tolerances for runout and size.
There are main types of spindle cooling systems:
- Liquid (it is based on the circulation of water or antifreeze in a closed circuit). One of the advantages is reliable heat dissipation. Among the disadvantages is a complex design, because the coolant must be placed in the tank.
- Air (such cooling consists in forcing air through slots-air intakes in the spindle cavity). Among the advantages of the system - compactness and simplicity. There is also a minus - filters, especially for equipment processing solid wood, must be changed often, they become contaminated with dust.
When choosing a spindle for a CNC machine, you should pay attention to its indicators indicated in the technical data sheet (power and speed during milling), which depend on how hard the materials are processed. For example, for sheet plywood, the required processing power is 800 W; over an array of hardwood, light metals - copper, brass and aluminum, plastic works more powerful machine - 1500 W; and the stone is processed at a power of 3000 - 4000 watts.
Now in equipment for milling, imported spindles are mainly used:
- Italian - high quality, running at high speed, with smooth rotation and low runout, mainly air-cooled and high price.
- Chinese has a solid cylindrical body, which is closed at the ends with covers, and bearing assemblies are used to hold the shafts. Among the advantages - the design has a sufficient level of rigidity and minimal vibration, insensitivity to the presence of chips and dust, affordability. Unfortunately, Chinese-made spindle models have a high probability of marriage, it can be difficult to replace bearings. And for models that have water cooling, there is a weak anti-corrosion resistance of internal parts.
Types of milling machines
Choosing such equipment, one must proceed from how it fits the purpose. The Russians have a choice:
- high-speed CNC automatic machines that cut and cut metals, process parts made of cardboard and wood, cope with two-layer plastic and acrylic, PVC, plexiglass and gypsum, natural stone - granite and marble;
- models (milling and engraving) working with sheets (maximum dimension 2000 x 4000 x 200 mm);
- engravers (from 2D modeling to 4D);
- narrow-profile machines that work with one kind of material - varieties of stone, plywood, wood, stainless steel or aluminum;
- small portable CNC models. For example, a milling machine model with "Desktop 3D" is used for milling printed circuit boards, MDF and processes products extremely accurately.
In the line of equipment series for professionals, you can give preference to vertical and horizontal machining centers with program control; large three-, four- and five-coordinate CNC milling engravers who produce in Taiwan.
They are considered quite reliable and buyable (after Germany and Japan - in third position). In addition, it is profitable to purchase them both for individuals and enterprises, due to the presence in Moscow and Tula service centers supplying equipment, cutting tool, adjustment of equipment and training of personnel.
ATTENTION: It is not difficult to distinguish a machine from Taiwan: it has a one-piece cast bed (the material of manufacture is Brazilian fine-grained cast iron). In addition, the machine is equipped with American or Japanese bearings, imported spindles.
And if the customer is looking for a high-precision jewelry machine, the best model for this is P 0403 from the manufacturer Vector.
furniture equipment
Woodworking and furniture manufacturing, workshops manufacturing windows, doors and facades will not be able to function without equipment of wide functionality - CNC woodworking machines.
In recent years, retro-style furniture has become fashionable - with elegant carved armrests, legs and other details. In this case, the technology of automated cutting of a pattern is used on a milling machine, on which numerical control is installed. It provides high precision and quality when complex wood milling is performed and a carved element is created.
With the help of such equipment, it is possible to establish the production of:
- wooden furniture facades and decorative consoles;
- balusters, curly legs and slotted elements;
- embedded carved details;
- symbols, figurines, figurines and frames of various shapes for paintings and mirrors.
Those who are on a budget may buy an inexpensive Chinese standard CNC router - CC-M1, especially for. In the manufacture of facades, engraving decor and bas-relief - usually a lot of dust. Therefore, choose the complete set, where there is a vacuum aspiration for dust absorption. This model has it.
What are the best milling machines? No one will give a definite answer. But there is still more trust in software working equipment. Each master has his own approach to choosing the right technique.
And the CNC router is good, which has higher accuracy, lower power consumption, more convenient to use, reliable in any working situation.
We can formulate three tips for the right choice:
- Specify in advance with company managers all the data about the model; materials with which the machine works. If there is a video, watch it. This will help you decide.
- Consult prior to purchase regarding the functionality of the equipment and the range of tasks performed. A the best option- sign up for a demonstration of the operation of the CNC machine and do not be shy to ask questions during operation.
- When the desired model is selected, be careful at the time of purchase: check the purchased equipment for a complete set of nodes. There must be a program control unit for the machine; cords with connectors of the appropriate configuration, and disks with software. Usually the software is installed by the specialists of the firm selling the machine during its adjustment.
Conclusion
Basically, we tried to help a person facing a choice. We figured out how to choose a milling machine (the thing is expensive, and will work with the owner for more than one year - with metal or wood). At least now there is plenty to choose from. I hope that readers will use this information to purchase a working tool.
The accuracy of machines in an unloaded state is called geometric. Depending on the accuracy characteristics, CNC machines are divided into four classes in order of increasing accuracy: normal H; increased P; high B; extra high A.
Machine tools elevated precision differ from machine tools normal accuracy mainly by more accurate execution or selection of parts, as well as specific features installation and operation at consumers. They provide processing accuracy on average within 0.6 deviations obtained on machines of normal accuracy. CNC machines high accuracy of class B provide processing accuracy within 0.4, and class A machines - within 0.25 deviations obtained on machines of normal accuracy. Machine tools of classes B and A are obtained as a result of a special design, their components and elements, as well as high manufacturing accuracy.
When checking the accuracy standards of machine tools, they establish * the accuracy of geometric shapes and the relative position of the supporting surfaces basing the workpiece and tool; accuracy of movements along the guides of the working bodies of the machine; the accuracy of the location of the axes of rotation and the trajectories of movement of the working bodies of the machine, carrying the workpiece and tool, relative to each other and relative to the basing surfaces; accuracy of the processed surfaces of a sample; roughness of the machined surfaces of the sample.
Accuracy check
The accuracy of CNC machines is additionally determined by the following specific checks: the accuracy of the linear positioning of the working bodies; the size of the dead zone, i.e., the lag in the displacement of the working bodies when changing the direction of movement; the accuracy of the return of the working bodies to their original position; the stability of the exit of the working bodies to a given point; the accuracy of working off the circle in the circular interpolation mode; the stability of the position of the tools after automatic change.
During checks, both accuracy and stability are revealed, i.e., the repeated repetition of the arrival of the working bodies in the same position, and stability is often more important for achieving the accuracy of machining on CNC machines than accuracy itself.
The total allowable error in the positioning of the working bodies Δ p = Δ + δ.
Based on the allowable deviations, the largest error in working out the movement, for example, 300 mm long along the axes X And Y for a class P machine it will be 17.2 microns, and for a class B machine it will be 8.6 microns.
To maintain the accuracy of the machine for a long time of operation, the norms of geometric accuracy for almost all checks in the manufacture of the machine, in comparison with the normative ones, are tightened by 40%. Thus, the manufacturer reserves a wear margin in the new machine.
Metal processing with high (precision) accuracy requires a special approach for the manufacture of machine tools. All precision machines are divided into classes according to the degree of extreme accuracy with which they are able to process parts:
- Class A machines (especially high precision).
- Class B (high precision equipment).
- Class C (machines of special precision).
- Machines class P (increased machining accuracy).
Precision equipment ensures the processing of parts with an ideal geometric shape, an especially precise spatial arrangement of the axes of rotation. The machines allow obtaining surface roughness up to the eleventh class of cleanliness. Manufacturing parameters, under certain conditions, reach the values characteristic of the first class of purity.
To achieve such indicators, it is necessary to use machine components and assemblies manufactured according to the relevant standards, with minimal errors in their production. Particular importance is attached to the bearings used. On precision machines for metal, high-class hydrodynamic and aerostatic bearings are used.
During the operation of metalworking equipment, a large release of heat occurs, affecting both the machine components and the workpieces. At the same time, both of them experience mechanical deformations, leading to a decrease in manufacturing accuracy. In high-precision machines, the function of active heat removal is implemented, which prevents geometric deviations of machine elements and parts. Reducing the level of unwanted vibrations also contributes to manufacturing accuracy.
Fundamentals of the theory of high-precision metal processing
Modern metal cutting machine can be considered as a kind of system of three components: measuring, computing, executive. None of them is perfect, each introduces errors in the accuracy of manufacturing.
The accuracy of the measuring part depends on the readings of the sensors used. The measurement accuracy is increased with the use of more advanced sensors - measuring devices. Today, such devices are able to track sizes down to several nanometers.
The performance accuracy directly depends on the units and assemblies of the machine. The higher the parameters of the components of the equipment, the smaller the final error will be.
The errors of metalworking machines include:
- Geometric, depending on the quality of manufacture of machine components and their assembly. This determines the accuracy of the location relative to each other of the working tool and the workpiece during processing.
- Kinematic errors depend on the correspondence of gear ratios in the mechanisms of the machine. Kinematic chains have a special effect on the accuracy of manufacturing gear elements, threads.
- elastic errors are determined by machine deformations. In the process of cutting, there is a deviation, under the action of emerging forces, of the relative position of the tool and the workpiece. In precision machine tools, to combat such manifestations, they create especially rigid structures.
- Temperature. Uneven heating of machine components leads to a loss of initial geometric accuracy, reducing the quality of workmanship.
- Dynamic errors are explained by the relative fluctuations of the working tool and the workpiece.
- Manufacturing and installation errors cutting tool.
Engines, gearboxes contain moving parts with backlash, sliding surfaces undergo wear over time - all this directly affects the quality of processing. Such a concept
as the positioning accuracy of the "machine - part" system directly depends on the performance accuracy.
Some are capable of machining parts with an accuracy of 0.0002 mm, at a spindle speed of 15,000 rpm. These figures also have a downside. The cost of equipment is much higher compared to conventional machines. This is a consequence of the use of the latest science-intensive technologies in the manufacture of machine tools. An example is the use of aerostatic guides, where the caliper with the working tool slides at a distance of a few microns from the surface. That is, in fact, it is in the "air".
A modern precision grinding machine is an automated complex that allows you to process parts with an accuracy of up to 0.01 mm. Serves for sharpening tools made of diamonds, hard alloys, tool steel. Ultra Precision grinding machines are able to process the internal and external surfaces of the part in one installation. precision drilling machine has a rigid structure, equipped with a digital display that displays the drilling parameters.
Common to all types of precision machine tools is the use of friction gears in drives. At the same time, the quality of workmanship is improved, kinematic chains are simplified. Higher efficiency reduces the cost of work.
Sorry for the delay in answering. I will try to make up for this with a complete description.
1. Swedish easy laser (D525, etc.)
The system is designed for various measurements and alignment of machines and mechanisms from small to large. Various types measurements: from alignment of shafts and pulleys to geometric measurements (flatness, straightness, etc.). There is partial compensation of influence environment.
It is a set of various lasers and receivers with brackets for fixing them.
Cost from 450 tr.
2. American Excel Precision's 1100B
Metrological system designed for machine tool verification. the tasks are quite standard: perpendicularity, flatness, parallelism, etc. There is a partial compensation for the influence of the external environment.
Cost unknown (did not receive a response from the manufacturer)
It consists of 2 modules: a laser and a receiver.
Accuracy 0.0005-0.0002 mm/m depending on tasks
3. Swedish Fixturlaser Geometry System
Very similar in functionality and parameters to Easy Laser.
It is a set of various lasers and receivers with brackets for fixing them. There is a partial compensation for the influence of the environment.
Cost from 600 tr.
Accuracy 0.01-0.02 mm/m depending on tasks
4. Italian OPTODYNE MCV-400 (etc.)
System for laser calibration and verification of machines and mechanisms. Represent a set of laser, mirror modules and receivers. There are environmental compensations.
Cost from 800 tr.
Accuracy 0.001-0.002 mm/m depending on tasks.
5. Estonian LSP30
In fact, it is a system for laser geometric measurements. those. the interface of the control program is poor. It is a laser interferometer module and devices for measuring various geometric parameters: flatness, parallelism, etc. There is no compensation for the influence of the environment.
Cost from 500 tr.
Accuracy 0.00025-0.0025 mm/m depending on tasks.
6. American Hamar Laser L-743.
a system very similar to the Renishaw ML10 with all the ensuing consequences. Various modules for turning and receiving the beam.
There are environmental compensations.
Cost from 1.5 million rubles.
Accuracy 0.0001-0.0008 mm/m depending on tasks.
7. American API XD Laser Measurement Systems
One of the most powerful systems in terms of application and accuracy. The same modular system, but with 3 lasers and multiple detectors and rotators. There are environmental compensations.
Accuracy 0.00005-0.0025 mm/m depending on tasks and system design.
Durability is unknown.
8. American PINPINT's PLS-100
Such an American "Lego" for checking the machine. Laser and various modules for turning and receiving the beam. No environmental compensation.
Accuracy 0.001-0.01 mm/m depending on tasks and system design.
Durability is unknown.
Each system is characterized by a maximum working distance, but even in the simplest it is not less than 10m. (for my tasks it is quite enough).
There are representations in Russia at Easy Laser and, in my opinion, at API. When I talked with Estonians, it turned out that at that moment they themselves knowledgeable person in China, but it seems that he should have returned already.
It seems that's all for now.
P.S. Right now, the management has finally realized the need for such a system and seems to be ready to order something from the above but inexpensive.
Good day!
About cheap! The cost, as a rule, consists of the requirements for completion, at least Laser head + Optics for linear measurements + Software and will be issued about 700 thousand rubles. with vat., kit for operation in a thermally constant room, or with manual input of environmental parameters and will work up to 40 meters. Just for normal operation, you need an auto-compensation unit, fasteners, a tripod, and so on. Here the cost goes to the line of 1.3 lemons.
A complete set will come out for more than 4 lyama. I can guarantee that the cost of a similar set will not differ much from the manufacturer.
Even we have European prices, when importing from abroad, others can save only on customs, which is fraught with a warranty case.
Here slipped statements about bad work in the St. Petersburg representative office, simply the incoming information is not always correct and it is often necessary to clarify "what the client wants to receive as a result" for the correct offer. Well, trouble, the St. Petersburg office was closed. :(
