DIY repair of mshu 125

In detail: DIY repair of mshu 125 from a real master for the site my.housecope.com.

Any power tool can fail over time. This usually happens due to a violation of the rules for its operation. The Bulgarian is no exception. If you have such a nuisance, do not panic and immediately call the wizard, because in most cases you can fix the problem yourself.

Figure 1. The device of the grinder.

To do this, you need to know the basics of electrical engineering and understand a little about the design of grinding machines. Next, we will consider how to repair the grinder with your own hands.

To understand how an angle grinder works, you first need to familiarize yourself with the principle of operation of this tool. With the help of electricity, the engine works, which, through a special gear, transfers the rotational movement to the shaft. At its end, a grinding or cutting wheel is fixed.

The high quality of work carried out with a grinder will depend on the number of revolutions of the cutting blade in 1 minute. With a professional power tool, this value can reach 10,000 rpm and more.

First of all, if a grinder breaks down, it should be disassembled and thoroughly cleaned; in most cases, the tool starts to work.

The layout of the grinder may differ slightly from different manufacturers, but the main parts are the same for all models (Fig. 1):

two-piece body;
electric motor of a certain power;
reducer;
electrical part.

The body is made of impact-resistant plastic. Its main task is to hold all the components in place and transfer the forces applied by the operator to the cutting element.

Video (click to play).

The electric motor drives the drive gear of the reducer, which rotates the driven gear, on the axis of which the disk is located. The reducer consists of gears through which the axis of rotation is rotated 90 °. Due to the use of gears of different diameters, the optimal speed of rotation of the cutting blade is achieved.

Before you repair the grinder, you need to prepare tools and materials that may be needed during the repair work:

tester;
screwdriver;
spanners;
knife;
tweezers;
sandpaper;
insulating tape;
grease;
alcohol;
rags.

The main principle that must be adhered to when repairing any power tool is that one should move from simple to complex, that is, the sequence of repair work must first exclude elementary malfunctions.

When an angle grinder fails, the first step is to remember the circumstances under which the breakdown occurred. This will most likely help to establish the cause of the breakdown, which will allow for a successful repair of the grinder.

The most common breakdowns of a grinder are open or short-circuited turns in the stator or armature windings.

The most vulnerable point of the grinder is the electrical part, the breakdown of which occurs most often. It can burn out from excessive loading of the tool during work, from water entering the device, from power surges, etc.

The mechanical part does not like abnormal operating modes, poor or untimely maintenance of bearings and gear elements of the gearbox, falling of the tool on the floor. Therefore, before you repair the grinder, you must thoroughly clean its body and trigger. If this does not help, then the grinder will have to be disassembled for further inspection and repair.

Very often a situation arises when the grinder suddenly stops working. The first thing to do in this case is to disconnect the device from the power source and manually rotate the disc. If it does not turn or turns very tightly, then you need to completely disassemble the tool and inspect its mechanical part. If the disc scrolls easily, then this means that power is not supplied to the brushes of the electric motor. This may be due to a failure of the power cord or the "Start" button.

The first step is to inspect the supply cable for integrity. Very often it bends at the point of its entry into the grinder's body. To eliminate such a breakdown, it is necessary to remove the cover from the handle of the device, and then ring 2 wires with a tester. If a break is found in any place, then it is better to replace the cable with a new one.

It is better not to do twisting, because in the place of twisting the wire will bend again after a while.

Grinder anchor device.

When the handle cover is open, you can immediately see the condition of the brushes on the armature collector. If they are worn out, they should be replaced. To do this, open the 2 windows of the brush holder and, by bending the spring, replace it. New brushes should be the same as the old ones.

Carbon deposits can form on the collector plates, making it difficult to apply the brushes evenly. In this case, the carbon deposits should be removed. To do this, take tweezers and wrap cotton wool around it. After that, take out the brushes, wipe them and the collector with alcohol, and then put the brushes back.

If, after these operations, the grinder still does not start, this means that the cause of the malfunction lies in the start button, which should be repaired. For repair, you need to disassemble the trigger. In this case, it is recommended to mark the removed elements, which will save you from incorrect reassembly. The serviceability of the button must be checked with a tester. If it turns out that it is defective, replace it with a new one.

Sometimes a situation arises when extraneous noise is heard during the operation of the grinder. To eliminate this problem, open the gearbox by unscrewing the 4 fixing screws. If the gear is worn out, replace it with a new one.

If the speed on the tool has decreased and strong sparking is visible from under the brush, then the armature insulation is broken. It is necessary to dismantle the old anchor and replace it with a new one. Such repairs are not always cost-effective, since the anchor is quite expensive.

Another weak point of the grinder is the bearings. This is due to the fact that the tool often has to work in dust, and the high rotational speed implies their rapid wear. Bearing wear is not the worst failure, because they are easy to change. The main thing is to replace them on time, as otherwise you may have more serious problems.

use the tool only for its intended purpose;
during operation, do not neglect the main technical characteristics of the grinder indicated by the manufacturer;
do not block the power tool;
carry out timely lubrication of the mechanical elements of the device, while using only high-quality lubricants;
carry out maintenance in accordance with the technological maps for equipment and to the fullest extent.

If, when working with a grinder, you adhere to all the rules and recommendations, then you can be sure that such a power tool will last much longer than its warranty period.

Read also: DIY nexia tachometer repair

Have you noticed that the tool always breaks the minute you need it most? And what to do? There is no time to run to the repairmen, and maybe not even run. Maybe try to repair it yourself? It was not the gods who did it. Let's take a grinder for a sample. Image - DIY repair mshu 125

Any, even a very complex mechanism, consists of large and small parts. The Bulgarian is no exception.Its main nodes and details:

Frame;
Stator;
Rotor;
Reducer;
Connecting wire;
Switch.

The assemblies can be divided into electrical and mechanical. Electric - stator, rotor, connecting wire. Mechanical - housing and gearbox. Of course, there is also a button, a fork, brushes.

Vala;
Windings;
Contact collector;
Brush holder and brushes;
Ball bearings.

For repairs, you will need a minimum amount of tools - an ordinary screwdriver with a special crown, pliers, a multimeter, electrical tape, thick grease for gearboxes. If we have all this, then you can start repairing yourself.

To simplify the task, troubleshooting and repairs must be performed systematically. There is no need to rush to disassemble the instrument. First, let's define the type of malfunction. The most important trouble is that the grinder does not turn on. What you need to check:

Serviceability of the power outlet;

Serviceability of the connecting plug;

The integrity of the connecting wire.

If these elements are in good order, then we inspect the contact brushes. Brushes are used to transfer the supply voltage to the contacts of the electric motor collector. The armature windings are soldered to these contacts. If one of the brushes does not contact or is broken off altogether, then the electric current will not flow to the winding and the grinder will not want to work. Image - DIY repair mshu 125

In order to inspect the condition of the brushes, you must:

Find two coaxial threaded plugs on the body;
Unscrew them carefully;
Remove the brushes.

The brushes are spring loaded, so you should try not to lose the springs. The removed brushes must be the same size. There will be some wear on them, but there should be no chips or transverse cracks that could break contact.

If the brushes are in good condition, you will have to inspect the engine armature. This node is only called an anchor, but in fact it has absolutely nothing to do with an anchor. This is the central shaft of the engine, on which the winding and the collector crown are located. Sometimes, due to heavy loads, a strong spark occurs between the brushes and the collector contacts. As a result, the copper contacts are covered with a layer of oxides and the current does not pass to the winding.

What needs to be done to put the anchor in order? We need to take the usual white rubber band, which is used by draftsmen and art lovers. Use the corner of the elastic to rub the contacts. The oxide film should be cleaned and shine with a copper sheen.

If this operation has not yielded results, then it is necessary to open the body of the grinder and inspect the condition of the internal wires, the phase-shifting capacitor and the winding. The winding should have an even color of the varnish with which the winding wire is covered. Darkening or blackening of the wire or its sections indicates a short circuit in the winding. It is difficult to fix this malfunction with your own hands; you will need to replace the anchor.

The task of the gearbox is to transfer the rotation of the electric motor shaft to the grinder's disk. Moreover, since we have an angle grinder, we also have an angle gearbox. To inspect it, you must:

Remove the disc, if installed;

Remove the protective cover;

Unscrew the four screws on the gearbox housing.

After that, the gearbox must come out of the housing. There are few faults here:

Breakage or significant wear of the gear teeth;
Shaft breakage;
Lack of fixation of gears on shafts.

Defective gearbox elements must be replaced. Replacing a gear is not difficult. The gearbox is then lubricated with a good layer of grease and reinstalled.

The stator is the part of the electric motor that is rigidly fixed in the housing. It is designed to create an electromagnetic field in which the armature rotates. Image - DIY repair mshu 125

The main malfunction of the stator is a break in the winding or its strong overheating. Why is overheating dangerous? When the winding wires overheat, the protective insulating varnish that covers them also overheats. Violation of the varnish insulation leads to a short circuit of the winding turns.

Even the closure of one turn of the winding completely disables the grinder. The winding immediately begins to overheat and smoke. The shaft rotates slowly or stops rotating altogether.

To repair the stator, you will have to change the windings to new ones or rewind. But rewinding the stator is not a procedure for beginners.

Any instrument must be treated with care. The design of a modern instrument asks for respect by its very appearance. The plastic case, although it has a margin of safety, is shock-resistant. Try to use special soft stands for any instrument. Image - DIY repair mshu 125

The housing has ventilation holes through which the motor is cooled. During operation, especially when cutting strobes, a lot of construction dust gets into the body. Therefore, after performing dusty work, it is necessary to blow out the inside of the grinder with compressed air. The outer surface of the tool must be wiped with a rag and dirt removed.

After completing the work, you need to remove the disc. This relieves stress on the drive assembly, and at the same time you can inspect and assess the condition.

Do not use a disc with a diameter that exceeds the size established for this grinder. A large diameter disc can be compared to a large lever, with which you try to destroy the mechanism of a tool or burn its electrical windings. In addition, it is not possible to install a protective cover.

After work, the electrical wire must also be wiped clean, remove dirt, and especially oil. The wire must be carefully wound onto a reel or at least onto the grinder's body.

Many power tool users have the bad habit of pulling the plug out of the socket by the connecting lead. Because of this habit, the wire breaks, the socket gets loose. This applies more to people who are sloppy and lazy by nature.

Avoid the possibility of water getting inside the grinder. When working in an open area, have a plastic bag or piece of polyethylene handy to cover the tool at all times to protect it from rain or snow.

In order for the grinder to serve for a long time and reliably, it is necessary to periodically open the gearbox, clean it and apply new grease.

Attention to a tool always has a beneficial effect on its long-term performance and your safety. And this should not depend on the brand of the grinder - it is Makita, sparka or our domestic sample.The grinder, being the most demanded tool in the house, is subject to considerable stress and intensive use. Because of this, after some time, it happens that when the engine is started, jerks, a burning smell and other malfunctions appear, suggesting that the angle grinder (angle grinder) has broken down. But do not immediately carry the device for repair or buy a new one. Most faults in this device can be rectified by yourself.

Over the long years of the existence of such a tool as angle grinder, its appearance, as well as its internal structure, have practically not changed. To repair a grinder with your own hands, you need to know the structure of its mechanical part, as well as electrical.If you look at the figure below, you can see what parts the angle grinder consists of.

Wheel for adjusting the spindle speed of the unit.

An electric motor consisting of a rotor and a stator.

Start button. Sometimes a soft start system is connected to it.

High impact plastic housing.

Spindle lock button (used when changing tools).

Safety clutch. Protects the motor from overload when the tool is jammed.

Protective cover. Covers the tool and protects the user from escaping particles of the processed material, and also prevents injury to a person when a tool is destroyed, such as an abrasive disc.

Tool clamping nut.It can be unscrewed using a special key that comes with the power tool. There are also quick-locking nuts that can be unscrewed without a wrench.

The gearbox housing and the gearbox itself. Consists of a block of gears that transmit rotational movements from the rotor to the spindle with the tool.

The picture below shows electric diagram of the grinder.The electrical part of the angle grinder has the following elements:

electric cable with a plug for connecting to the mains;

start button;

stator;

electric brushes (carbon or graphite);

collector;

anchor (rotor).

The following figure shows grinder connection diagram, namely its engine.All components of an electric motor perform specific functions.

Rotor - this is the shaft on which the coils and the collector are located. The rotor, rotating in the magnetic field of the stator, transmits the rotational motion to the angle grinder.

Collector... It is the part of the rotor to which all control cables are connected. Electrical signals from the control unit to the engine pass through the manifold. It is to the collector that the electric brushes are connected.

Electric brushes. Their main task is to transfer electric current from the power cable to the collector.

Stator. It is a coil with a certain number of turns. The task of the stator is to create a magnetic field, which, interacting with the armature, sets the latter in motion.

According to statistics, most cases of failure of angle grinders are associated with the electrical part of the apparatus. Some breakdowns may be minor, which allows you to repair the grinder yourself. But, for example, if the motor windings burn out, only a specialist can repair the angle grinder.The reasons that the angle grinder does not turn on may be the following:

defective electrical plug;

defective electrical cable;

the start button has broken;

broken contact between the power cable and the button;

breakage of the contact wire of the electric brush;

strong wear of the electric brushes;

failure of the rotor or stator windings.

There may be different reasons for the angle grinder not picking up speed.

Breakage of the speed control unit... To test this version, it is necessary to connect the engine of the device directly, bypassing the regulator, and check the operation of the device.

Faulty electrical cable due to constant bending or mechanical damage. Because of this, the damaged wire begins to warm up under load, and the engine speed drops.

Dust contamination of the collector... Remove contamination with alcohol.

Brush problems... They may wear out or have a short contact wire, as shown in the following photo.

The brush, although half worn out, is quite functional. In this case, the short contact wire prevents the spring from pressing the electrode against the collector. This situation can also be the reason why the angle grinder stopped working in normal mode.The reasons why the grinder is heating may be as follows.

Incorrect mode of operation of the device... As a result of overloads, the electric motor can become very hot, which often leads to burnout of the windings.

Bearing failurelocated at anchor. As a result, the rotor clings to the stator, the motor becomes difficult to operate, and the windings overheat. The problem is solved by replacing the bearings.

Clogged ventilation ductsthrough which air enters to cool the engine. It is necessary to clean the ventilation openings from dust.

Impeller breakage, which serves to cool the engine. It is installed on the rotor, on the side opposite to the collector. If the impeller is broken, it must be replaced with a new one.

Turn-to-turn closures stator and rotor windings. You will need to rewind the coils or replace these parts with new ones.

If you notice strong sparking when turning on the angle grinder in the place where the collector is located, then the reasons for this trouble may be as follows.

To diagnose the electrical part of the angle grinder, as well as eliminate mechanical damage to the device, you will need to disassemble it. Disassembly is carried out according to the following algorithm.

Unscrew the handle.

Remove the protective cover.

Open the special windows located on the sides of the casing of the angle grinder, and remove the electric brushes, having previously disconnected the terminals.

Unscrew the gearbox housing from the LBM motor housing.

Pull lightly on the gear housing and detach it from the housing. In this case, the gear unit will be removed together with the rotor.

After removing the armature, the motor stator will remain in the casing, which is also easily removed for diagnostics after unscrewing the fasteners.

To disassemble the gearbox, unscrew the screws holding the cover. Removing the cover reveals the gears of the reducer.

To remove the anchor from the grinder, you will need to unscrew the nut located inside the gearbox.

In order to remove the bearing from the armature, it is recommended to use a special puller. Otherwise, the shaft could be damaged.

As mentioned above, most often the angle grinder refuses to work due to breakdowns in the electrical part of the unit. For the correct diagnosis of the electrical circuits of the instrument, the repairmen of electrical equipment use a special device - tester.

If you pressed the start button of the unit and it does not work, then in 90% of cases the cause of the breakdown is not so serious that you cannot repair the grinder yourself.

Experts advise adhering to the basic rule of repairing a power tool: move from simple to complex.

The first step is to checking electrical cable and plug at its end. If it is collapsible, then unscrew it and check the reliability of the contacts. Otherwise, you will have to disassemble the grinder (remove the cover of the device) and “ring” the cable with a tester, and also make sure that the current goes to the contacts of the “Start” button. If the device shows a break, then the cable should be replaced with a new one.

The situation when the current flows to the button, but does not pass further (when the position is on), indicates switch malfunctions... The button cannot be repaired. It must be replaced with a new one, but first mark the removed contacts in order to connect them correctly in the future. If the contacts are incorrectly connected, the motor winding may burn out.

If during the check it turned out that both the cable and the start button are in good order, but no current flows to the brushes, then it is necessary to make cleaning the contact plates of the brush holders... If this procedure is ineffective, it is recommended to replace the brushes. Further, if everything is fine with the brushes, and the current flows to them, the rotor and stator should be checked for shorts and breaks.

The rotor of the electric motor may have the following faults: interturn short circuit and wire breakage at the contacts of the lamellas. You can check the grinder's anchor with a multimeter: the device is switched to the resistance change mode, the value is set to 200 Ohm, and the resistance between two adjacent lamellas is measured with the help of probes. Thus, it is required to check all pairs of lamellas. If the resistance values are the same, then the rotor winding is not damaged. The detection of other resistance values during the “ringing out”, as well as the detection of an open circuit, indicates a malfunction in this coil. In this case, you will need to repair the grinder's anchor.

Usually, the break of the conductors occurs at the junctions with the winding. Inspect the places where the coils are connected to the lamellas, make sure that the contacts are soldered securely.

If you do not have a measuring device, then you can check the rotor by using 12 V light bulb and battery... The power should be between 30-40 watts. The check is done as follows: apply a voltage of 12 V from the battery to the plug of the angle grinder, connect a light bulb to the break of one wire, start rotating the spindle of the angle grinder. If the winding is in good condition, the light will burn evenly, without blinking. With an inter-turn closure, the degree of incandescence of the spiral of the light bulb will change. In this case, repairing the grinder's anchor with your own hands will be difficult, since the anchor winding scheme is quite complicated, and the process itself requires special equipment and knowledge. Therefore, it is recommended to entrust this operation to specialists. But the best way out of the situation would be to replace the anchor on the grinder with a new one.

If the light does not light up when testing the rotor, this indicates the presence of an open in the stator or a short circuit in its windings, as well as problems with the electric brushes.

To check the stator of the grinder, use, as in the previous case, a multimeter. The values you need set to 20-200 Ohm and do the following. Touch one probe to the contact of the stator winding, and the second to the body of the part. If the device shows resistance, it means that there has been a breakdown to the case. Touch the probes to the contacts of one winding, and then to the contacts of the other. If the resistance is the same, then the coils are serviceable. If the device shows an open circuit on one winding, it means that you will need to rewind the stator or replace the part with a new one.

It will be problematic to rewind the stator at home without special knowledge, skills and equipment. It is better to contact a specialist who is professionally engaged in motor rewinding.

Mechanical breakdowns of angle grinders include the following.Mechanical failures include breakage of the shaft retainer. In order to replace the retainer, you will need to disassemble the gearbox and remove the large gear.

Any angle grinder consists of the following units and mechanisms, the location and condition of which should be understood with confidence:Layout and electrical diagrams, as well as detailed instructions for the exact model of the grinder that you want to repair, will be an extremely desirable assistant in the repair. Unfortunately, many manufacturers do not burden their devices with such excesses. In this case, the necessary information can be gleaned from the know-it-all Internet and not to repair the grinder with your own hands, counting on "maybe everything is simple there", of course, if you do not want to buy a new tool following the results of the repair procedures ...

So, we open the device and see a bunch of dust and dirt that has accumulated over a long time of operation, we clean it all and wash it with napkins and degreasers.

We check the brushes, and all the electrical connections at the terminals by tightening and cleaning, take out the rotor of the collector electric motor and check it by visual inspection of the winding and plates so that nothing sticks, the bearings must be intact without cracks, and they must rotate freely without jamming, noise and backlash ...

Next, we proceed to the switch, as it turned out, and became the culprit, here the switch button commutes two conductors of the circuit at once. We purge the lever drive itself with silicone grease so that it can more easily walk in its groove in the guide to the switch itself.

The switch can be removed and disassembled, I could not repair the burned-out half, so I closed one of the wires directly, and the second now serves to turn it on and off.

Over time, the contact went away in the switch, began to spark and heat up, and part of it melted.

You can, of course, replace the entire switch, which would be correct, but the owner wanted it as cheaply as possible, since the tool is not very expensive, and it’s not new, so I had to do this, a new switch costs about 400-500 rubles in the city, which not very cheap.

After assembling the grinder, be sure to test and check the operating modes at idle speed before giving it to the owner.

As you know, nothing is eternal and even the tools of brand manufacturers break, not to mention the so-called “consumer goods”. And the grinder (angle grinder) is no exception. By the way, they began to call angle grinders "grinders" at the time of the Union, because then this instrument was produced in Bulgaria and the first models were supplied from there. The grinder, as a tool, has become very widespread due to its versatility and ease of use. There are also many varieties and models of grinders, but the principle of operation and device is not fundamentally different. Therefore, having considered the device of the tool, possible malfunctions and repair methods, they can be applied to any model of the grinder.

Grinder device relatively simple. The basis of the tool is its body, inside which there is an electric motor, a starting device and a gear transmission to the spindle, on which various attachments are attached.

The body is made of strong impact-resistant plastic. Depending on the power, there are different dimensions and shapes of the tool. Some models have an angular speed regulator, which is designed to optimally select the speed for various types of work.
Another component could be a gearbox. The gearbox is designed to create optimal conditions for the transfer of rotation from the rotor of the electric motor to the cutting or grinding wheel. This leads to a decrease in the number of revolutions on the output shaft of the gearbox. Correctly selected rotational speed and wheel diameter are the key to the most efficient tool performance.

A button for replacing the working disk, when pressed, which locks the disk in a certain position, preventing it from scrolling when removed.

The overload clutch acts as a limiter in the event of a sudden reactive torque. On the other hand, when the disc is jammed in the material, the grinder itself begins to rotate abruptly, which can lead to injury to the worker. This clutch does not allow such rotation.

The electric motor consists of a stator and a rotor as standard. The stator is located in the guide lugs of the plastic housing of the grinder. On the back of the stator there is a special device called a brush mechanism. It contains copper-graphite brushes. Brushes are required to transfer voltage to the rotor through the manifold assembly.

The rotor is located inside the stator and is fixed in the housing in bearing assemblies, which are inserted directly into the tool housing. The front bearing assembly is usually made in a metal plate, or this plate can be made of an aluminum alloy.

The gearbox housing of the grinder is almost always made of aluminum alloy and has several threaded holes for attaching an additional handle. By screwing the handle into various holes, you can change the planes of location during operation.

The reducer consists of two gears, with the help of which the direction of the output shaft changes by 90 degrees and the rotation speed is reduced. The ratio of the number of teeth on the primary gear to the number of teeth on the secondary gear is called the gear ratio.

The grinder suddenly stopped working.
The first thing to do is disconnect physically from the network and manually rotate the disc. If the disc does not spin or is spinning very tightly, immediately disassemble the instrument for visual inspection. If it turns easily, then the most likely thing is that electricity does not reach the brushes of the electric motor. That is, the problem lies either in the power plug, or in the wire itself, or in the mechanism of the “Start” button. It is enough to disassemble the case and “ring out” the cable with an ordinary tester, or in some other way, for the presence of a break. After eliminating the break or replacing the wire, the grinder will work.

The wire and plug are guaranteed to be intact, but the tool still does not work.
It is necessary to disassemble the trigger mechanism, and it is advisable to mark the removed contacts - if they are subsequently connected incorrectly, then the winding may burn out or the anchor may jam. Repair of the trigger mechanism is not often possible - it is easier and more reliable to replace the trigger button with any similar one with suitable power parameters. Such a button is not so expensive and you can buy it in any store of the corresponding profile.

Then there are more serious malfunctions, respectively, and repair requires certain knowledge and skills.

- breakage or licking of the gear teeth of the gearbox;
- jamming of bearings;
- failure of the armature or stator;
- failure of the control electronics;
- failure of the collector;
- deformation of the body;

When determining the mechanical defects of the grinder, more attention should be paid to the condition of the plonitarka (large gear), shank (gear on the shaft) and bushings. Uneven wear of the teeth or wobbling of the shafts indicates immediate replacement of the worn parts.

Breaking out the spindle lock button.
The reason is just one careless movement, namely pressing (deliberate or accidental) on the button when the disc is spinning. Sometimes breakdowns occur due to attempts to remove a jammed disc using a button. Many grinders have slots on the spindle where the disc is attached specifically for a regular open-end wrench, look at your grinder, most likely you have one too. So, it is better to use them and an open-end wrench than a disc lock button.

Chipped gear teeth.
Usually they arise due to jamming (in such a situation, tool breakage is not the worst thing that can happen). A rumble in the gearbox is a sign of a malfunction. If the gear has lost two or three teeth, then the tool will not be able to cut.
In this case, it is necessary to change the gears by a pair and the gear itself and the bevel wheel. When you go to the store for gears, do not forget to write down the name of your grinder and its power.

Failure of the electric motor.
This often happens with tools that work in dust and which are forced to rest in the sand or on the ground: the sucked-in dust grinds off the winding. However, you can ditch the motor without dust - by strong overloads, especially if the tool is low-power. Therefore, in small Bulgarians, not only the anchor, but also the stator often burns out. Small grinders also have a breakdown of the electronic speed control unit. If you use a grinder to cut very dusty materials, in particular slate, a stocking put on in place of the ventilation slots in the housing helps a lot to protect the tool.

Bearings.
Another sore spot of the Bulgarians (as well as other twisting power tools). Few machines stand out with strong immunities against dust, and high rpm suggests rapid wear. In general, bearings are not the worst failure, they are easy to change. However, it is important to make a replacement on time, otherwise there is a greater likelihood of a more serious breakdown, the repair of which is comparable to a purchase.

Stator
If, when turned on, the disk starts to gain speed and accelerates too much, there is definitely a turn circuit on the stator winding. Stator repair is one of the most serious breakdowns and requires appropriate skills. If you are not confident in your abilities, then it is more expedient to entrust it to professionals or use the services of a repair shop.

We start repairing the grinder's stator by cutting off the frontal parts of the winding, the remnants of which we take out.Next, we make a new winding using a template sandwiched between two large plates on an axis, which can be inserted into an electric drill. The main thing is to achieve an identical number of turns, made with the proper density and withstand the thickness of the wire. We insert two coils into the stator housing, we draw conclusions from the same winding wire, insulating with flexible tubes of the appropriate diameter.

Reducer
In models with a power of up to 1100 W, spur gears are usually used, mounted on an anchor, but grinders with a higher power, for example, 1500 W, require helical gear wheels. Both options are tapered, since the axis of the gearbox stem intersects with the armature shaft, and transmission is possible only by angular engagement of the teeth.
As a rule, repairing the grinder's gearbox consists only in replacing the gears. If a disk gear wheel breaks down, then it will be very difficult to remove it for replacement, this unit is best fixed in the gearbox.

Speed regulator
Almost all modern models of drills, jigsaws, screwdrivers have a speed controller. But not all grinders (grinders) are equipped with such a mechanism. In principle, a regulator is not needed for cutting metal with a cut-off stone, but for grinding it simply cannot be replaced. The proposed scheme of a home-made regulator is very simple and reliable. There are not many parts and they are not expensive. If you already have a grinder without a standard speed governor, then you can easily improve it.

Can be assembled separately in a box with a power outlet and used as a carrier with a power regulator. Or you can immediately assemble the regulator in the grinder body and remove the resistor handle.

The power tool must not be allowed to operate under load for a long time at significantly reduced speeds (this can be determined by ear) in comparison with idle speed, and even more so, clamping (blocking) of the tool must not be allowed, otherwise it will burn out within a few seconds.

Do not turn off the power tool immediately after operating at reduced speed. To prevent local overheating, it needs to run for some time (more than 1 minute).

It is important to strictly observe the intervals for changing (adding) the lubricant and its quantity specified in the operating instructions.

Video (click to play).

Prevention consists in complete or partial disassembly of the tool, cleaning, lubrication and replacement (if necessary) of some parts.
Timely replacement of relatively cheap parts that wear out quickly will preserve more expensive durable components, which ultimately will lead to savings in tool operation, eliminate premature repairs and significantly extend the life of the tool.

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