Do-it-yourself Interskol grinder repair

In detail: do-it-yourself repair of an Interskol grinder from a real master for the site my.housecope.com.

Recently they brought a grinder for repairs, it doesn’t work, and in general it works when it wants to. In general, Interskol devices are very reliable and durable, their quality, as a rule, is good and they work reliably and for a long time, well, since it does not work, we will repair it then.

Power consumption: 900 W
Rated voltage: 220V / 50Hz
Rotational speed: 11000 rpm
Circle diameter: 125mm
Rotary main handle: no
Weight: 2.2KG

Image - Do-it-yourself Interskol grinder repair

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.

Of course, you can completely replace the 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.

Video (click to play).

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

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 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 is unscrewed with 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 angle grinder casing and remove the electric brushes after disconnecting 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 malfunctions: 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, the grinder's anchor will need to be repaired.

Usually, the rupture of conductors occurs at the junction 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 an open in the stator or a short 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.

Do-it-yourself grinder repair is a completely solvable task. The main thing is not to rush, to understand the structure, remember all the circumstances under which it broke down, determine what could have worn out during operation, make diagnostics and start repairing it.

Angle grinder (angle grinder) is called a grinder. The name of the instrument is due to the fact that it was produced by the Eltos-Bolgarka plant in Plovdiv. It is designed to perform work on grinding or trimming hard material:

Performs well sharpening of the tool.

Nowadays, a grinder is a very necessary tool, so almost everyone has it.

There are grinding machines of different power: from 500 W to 2500, depending on the thickness of the wheel - from 115 mm to 230 mm. The most popular in the work are angle grinders with a power of 1.2 W, and the most used disc is 125 mm thick.

Every year the choice for this construction power tool is becoming wider, but the operating rules hardly change. And even if you always adhere to them, sooner or later there are malfunctions in the mechanism that you can try to fix with your own hands, collecting everything you need to repair the grinder.

Any grinder consists of the following parts:

rotor - a part of an electric motor that rotates during operation and is speed-controlled, also called an anchor;
collector - the place on the rotor where the control winding wires are located;
brushes - parts that serve as conductors of current from the cable to the collector winding;
reducer - a mechanism that acts as a drive from a rotating rotor to a rotating disk, consists of a spindle, a bearing, two gears (large and a shaft gear);
stator - the part of the electric motor in which the rotor works;
grinder cooling impeller;
start button;
network cable with electric drive;
protection casing;
grinder body;
additional handle.

All these details can be divided into two parts:

How to disassemble a grinder? Not such a difficult process. This does not require special knowledge, but everything must be done carefully and carefully. Each owner needs to know how to disassemble any working tool, because from time to time it needs to be cleaned internally from dirt and trapped dust, and its durability depends on it.

At the present time on the market, you can choose for yourself a different type of grinder, which differ in performance, size, quality. Manufacturers are also different. Whichever model of grinder you buy, everyone has the same assembly model.

Dismantling the grinder will require few tools, you just need a regular screwdriver or a reversible screwdriver with a ratchet mechanism.

Having prepared a screwdriver, you can start disassembling:

We unscrew the screws from the body and remove one side of the product.
Remove the nut that holds the disc, unscrew the bolts securing the protective casing.
We remove the brushes.
Disconnect the wires from the engine.
We unscrew the bolts that secure the gearbox inside, and very carefully remove it, and the rotor is also removed with it.
We unscrew the bolts that hold the stator and remove it.
We put the grinder back, put everything in place in the reverse order and fasten it.

When disassembling the grinder, it is important to remember the order in which the parts are removed in order to assemble them correctly.

In the event of a malfunction, first of all, it is necessary to exclude elementary breakdowns:

The grinder does not turn on. The angle grinder suddenly became faulty - it stopped turning on. In this case, you need to check the serviceability of the outlet, then the plug and the power cord, perhaps the drive simply does not work due to the fact that no current flows into the product.

The cable and plug are intact, but the drive does not work. You need to check the start button. It is easier to repair the grinder switch by purchasing a new button and replacing it. Since it rarely needs to be repaired - basically, the plastic rod of the switch breaks inside. If you want to experiment, you can disassemble it by numbering the contacts, and put everything back together in place so that after assembly does not happen a short circuit.

The above parts are intact and the angle grinder doesn't want to work - so it's time to check the brushes. Perhaps it's time to change them in the grinder. The brushes are constantly heated from work, so they wear out quickly and more often than other parts need to be replaced, and in pairs.

Having excluded all minor breakdowns, it is necessary to understand why the tool does not want to turn on, and how to repair it. Most likely, the malfunctions are serious and require additional knowledge. This happens if:

the body is deformed;

one of the bearings is seized;

the armature or stator does not work;

the teeth of the gear wheel of the reducer are broken or worn out;

the collector is out of order;

the sensor of the control electronics does not show signs of life.

If it is determined that a malfunction has occurred in the mechanical part of the grinder, then you need to pay attention to the condition of the large gear located on the shaft, and to the bushings. If the teeth are partially worn out or the shafts are wobbling, they must be replaced immediately.

The most common breakdowns

Grinder malfunctions happen quite often. Everyone who works with this tool knows about this. What goes wrong most often?

Just one awkward pressing of the spindle lock button while the disc is rotating will break it. It can sometimes be broken if used to remove a jammed disc. To prevent this from happening, you need to use an open-end wrench inserted into the special holes near the place where the disc is attached.

It mainly occurs when a jam occurs. If a rumble is heard in the gearbox, this is a symptom of just such a malfunction.When more than one tooth is broken at the gear, the grinder will not be able to cut the required material.

In order for the tool to continue working, it is necessary to change the gears, and everything, and even the bevel wheel. Before going to the store for spare parts, remember the manufacturer's firm, the model and the power of the product.

This type of breakdown happens with angle grinders, which work in places where there is a lot of dust, and when they are given rest, they are left on the ground. Dust that gets inside will damage the winding. Large loads, especially for a small power grinder, turn into a motor breakdown.

Read also: DIY linoleum joint repair

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 ...