Angle grinders in Soviet times were made in Bulgaria. Therefore, angle grinder began to be called an angle grinder. Currently there are many companies producing angle grinders of various models. But the basic elements are the same. Having familiarized yourself with the device, possible breakdowns and tool diagnostics, you can repair the angle grinder of any modification with your own hands.
The device and purpose of the angle grinder
angle grinder is designed for grinding and cutting various materials.
The main elements of the angle grinder
The angle grinder consists of the following elements:
- The aluminum alloy flat gear housing dissipates heat better.
- Carbon brushes.
- Grip mount
- Electronic soft start system. Prevents jerking when turned on and reduces starting loads on the engine.
- Quick detachable guard.
- Ball bearings.
- Electric motor
- Switch angle grinder.
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Main malfunctions, their causes and diagnostics
The main breakdowns and causes:
- Burns, sparks and twitches. Reasons: violation of the insulation of the armature winding, wear of the brushes, collector, clogging of the brush holders. Even after replacing the brushes, the angle grinder sparkles and twitches if the brush holders are clogged.
- Clapping sound. Brushes or interturn circuit of any of the windings.
- Crispy sound. The reason is in the bearings.
- Mechanical rumble and heavy tapping. Gearbox malfunction.
- angle grinder has stopped working, does not turn on. If the disk is manually spinning tightly or not spinning, the cause is the gearbox. If it turns easily, check the electrical circuits. If chains work, check motor and brushes.
- The spindle lock button has broken. The reason is clicking on it during rotation of the disc or jamming of the disc.
- The angle grinder works in fits and starts. Check engine for interturn short circuit.
- Vibrates. The reason for mechanics. Check bearings, rotor shaft and gearbox.
- Heats up. If it heats up in the engine area, the cause is worn out brushes or a short circuit in the turns of the windings. If the gear case is warming, then the grease has dried or the gears have worn out.
- It does not gain momentum or power drops. The reason is in the electronics or engine. Check soft starter control board and speed controller, brushes and collector.
- Smokes. The reason is overheating of the tool. Check motor windings for insulation melting.
- Humming and not spinning. Check motor bearings and gearbox.
How to disassemble and reassemble the angle grinder
To troubleshoot the angle grinder must be disassembled.
- Remove the nut that holds the working disk.
Turn off bolts of fastening of a protective casing.
Remove the housing bolts from the angle grinder and those that secure the housing to the gearbox.
Remove the top of the rear housing. Turn off bolts of fastening of a cord. Remove the wires and button from your grooves. In some models, for example, in DWT, the rear case is not disassembled into parts, but is removed entirely.
Remove the gearbox bolts located around the casing mount.
To disconnect the anchor from the aluminum housing, unscrew the nut located in the gear housing.
Reassemble the tool in the reverse order.
The clamping nut is not untwisted
During operation, the disk can tighten so tightly with a nut that it begins to crumble. It is not possible to unscrew the nut with a wrench. And you do not need to do this, since you can break the angle grinder. First, break the disc all the way to the nut. Then find the metal plate a little thinner than the working disk. Use it to drain off the rest of the disc under the nut. It can be easily unscrewed with a key or hands. In order not to bring the tool to this problem, put the washer under the nut.
How to remove a tightened nut
The casing cannot be removed
In some grinders, for example, Bosh, the casing is not bolted, but latched. To remove it, you need to turn the cutout of the casing perpendicular to the angle grinder. To dress, turn until it clicks.
The stator is checked with a multimeter.
- Inter-turn closure. Set the resistance mode to 200 ohms. Connect the test leads to the ends of one winding. A unity means an open, and zero means a short circuit between the turns. If it shows a resistance of more than 1.5 ohms, then check the second winding. Both windings should have approximately the same resistance.
- Breakdown on the mass or shorting of the winding with the metal housing of the stator. In the multimeter, set the maximum resistance mode. Connect one probe to the end of the winding, the other probe to the metal housing of the stator. The unit indicates the absence of breakdown.
First visually inspect the collector and winding. There may be visible damage: black marks, bent turns of the winding, raised, worn or burnt collector plates. After inspection, proceed with the tester.
- Set the resistance to 200 ohms. Connect the test leads to two adjacent collector plates. If the resistance is the same between all adjacent plates, then the winding is working. If the resistance is less than 1 ohm and very close to zero, there is a short circuit between the turns. If the resistance is above the average two or more times, then there is a break in the turns of the winding.
The determination of the breakdown to mass is done in the absence of a winding break. Put the maximum resistance on the scale of the device. Depending on the tester, it can be from 2 MΩ to 200 MΩ. Connect one probe to the shaft, and the other to each plate in turn. In the absence of faults, the resistance should be zero. Do the same with the rotor. Connect one probe to the iron body of the rotor, and move the other along the plates.
Checking the power button
Put the tester in dialing mode.
Insert one probe into the output of the button and the other into the opposite input.
Click the button. A sound signal indicates the health of this part of the button.
Do the same with the other input and output of the button.
How to ring the start button
Power cord check
Connect one probe to the plug pin, the other to the button inputs. In one of two positions there should be a sound signal. Do the same with the other pin of the plug.
Check soft start and speed control
If the power button and power cord are working but the engine does not turn on, check the softstart control board. Remove the screw that secures the control board. Remove it carefully. Call all items. If there is a speed regulator in the angle grinder, then it can be connected in series with the power button and have one board with soft start. But may have a separate fee. It is checked similarly to soft start.
Precautions before starting repairs
- Read the instructions. Read the description and assembly diagram of the angle grinder.
- Unplug the tool.
- Prepare a workplace on a table with good lighting.
- Recorded on paper or on the photo order of disassembly tool to assemble it correctly after repairs.
If you are unsure of your abilities, it is better to take the tool to the workshop.
Power cord and power button
Damaged cord and button must be replaced. On the button, unscrew the bolts securing the incoming and outgoing wires. Disconnect it from the chain and install a new one.
Soft start and speed control
If only the triac is out of order in the control board, then a new one must be put in its place. Pre-grease the metal part of the element with thermal grease. If other elements of the board burn out, replace it completely.
Brushes must be checked periodically. When one is worn by 40%, change both. And also clean the brush holders.
- To remove the brushes, you must either remove the rear housing or remove the plugs in the housing.
- Clean brush holders of dust and carbon deposits. Wrap a cloth around the screwdriver and moisten with alcohol. Nagar is cleaned off with a file. The brush should walk easily in the brush holder, then it will be well pressed by the spring.
- Insert new brushes.
Brush holder cleaning
For high-quality winding coils, you will need an enamel wire and an electric cardboard.
Remove the winding and old insulation from the housing. Look carefully at the slots. When the coils burn, insulation is burned and a short to the case occurs. Deposits remain on it, which must be removed with a file or a diamond bur. Deposits will interfere with the new winding. She may tear.
The winding is saturated with varnish. To disconnect the wires and count them, you need to strip out the insulation. Preheat the winding with an industrial hairdryer or any burner.
Burn matches or lighters with any fire to make the enamel completely burnt out. Take a micrometer and measure the thickness. Record wire diameter and number of turns.
Take any wire and make a loop out of it so that it fits in the grooves of the stator. Under the diameter of this loop, select a cylinder for winding coils. For example, spray can. If its diameter is not enough, then wrap the can with paper.
Wrap both windings from the enamel wire. Fasten the frontal parts with glass tape or thick thread. The thread should not break and melt. At the loose ends, put on shrink cambric.
Make sleeves from the electric cardboard and insert them into the grooves. Place the windings in them.
Check the resistance in the windings of the tester. If everything is fine, continue.
So that during operation the wires do not vibrate and do not rub against each other, they must be impregnated with any oil-based varnish. Put the starter preheated in the oven vertically and squeeze the varnish onto the winding with a syringe. When the varnish starts to leak from below, turn the stator over and soak on the other side.
When the varnish is dry, proceed to connect the windings. Connect the two ends of the different windings to each other and connect to the nearest brush. Connect the other two connected ends to the start button. Connect the wire from the second brush to the button.
Rewind stator on video
If the balance is disturbed, the anchor must be replaced. The winding and collector are subject to repair. Small short circuits are eliminated. If a significant part of the winding is damaged, it can be rewound.
A not very developed collector is corrected by a groove. But if the plates are erased to a plastic base or partially burnt out, then the restoration is carried out by soldering or galvanic building.
Badly damaged collector
If the collector was completely worn out, then after soldering it will be enough for no more than a month of active use. And not completely damaged plates after such a repair can withstand several brush changes and do not evaporate. You will need to cut the copper plates in size and solder them with a lot of solder. Strain excessively with a file and polish.
With galvanic build-up, reduced copper is very solid. The life of the collector is like new.
Completely restored collector
By galvanic build-up, it is possible to restore both a completely wiped collector and partially damaged plates. The restored collector must be grooved and the plates divided with a drill or hacksaw blade.
In order to rewind the anchor correctly, you need to correctly disassemble it and remove the parameters for the template:
- Winding direction.
- How many grooves and slats.
- The number of conductors in the groove.
- The winding pitch, i.e. how many grooves between the grooves of one section. For example, if the conductors exit the first groove and enter the sixth, then step = 5.
- How many conductors are in one groove, so many coils in one section.
- Wire thickness.
For example, 80 conductors in a groove, 12 lamellas and 24 grooves. 12 sections of 2 coils. The winding passes in two circles, so we divide 80 conductors in the groove by 2, and another 2, since there are 2 coils. We get 20 turns of one coil.
Anchor winding pattern
- We solder the beginning of the wire to the lamella 1 and pass it through the first and sixth groove. We make 20 turns. The first coil of the first section is ready.
- We solder the wire on the lamellas 2 and repeat the winding through the same grooves. The second coil of the first section is ready.
- We solder the wire on the lamellas 3. Pass the coil through the second and seventh groove. We wind the first coil of the second section and solder the wire to the lamellas 4.
- The second coil of the second section is fixed on the slats 5.
How to remove the old and rewind a new winding:
Use a hacksaw or wire cutter to remove the frontal parts of the winding.
Carefully, without damaging the slot insulators, knock out the rods of the remaining parts of the winding with a hammer and a metal chisel.
Use a file to remove any remaining impregnation. Count the conductors in the groove and measure the diameter of the wire. Draw a diagram. Cut the insulation sleeves from the cardboard and insert them into the grooves.
After winding, weld the conclusions of the sections with the collector plates. Check the winding with a tester.
Soak the winding with epoxy.
Bearings crumble or jam over time. They need to be changed.
- Disassemble the angle grinder, remove the anchor from the stator.
- An anchor is inserted into the gear housing by a bearing. If the housing cannot be removed, fasten the rotor in a vice and tap the gear case with a wooden block.
Gearbox disassembly and repair
The gearbox must be disassembled not only for repair, but also for preventive cleaning and lubrication.
Video: How to Remove the Gear From Bosch Angle Grinder
- Remove the bolts and disassemble the gear housing. You will see dirty grease that needs to be removed.
old grease will spill out of it. Clean parts with a rag or toilet paper. Flush the housing and parts with kerosene.
Apply new grease recommended by the manufacturer in the tool manual.
Spindle lock button
If the button has flown out, then such an angle grinder cannot be operated.
Spindle lock button
Since the spindle can spontaneously lower to the gear and block it during operation.
The locking unit consists of a spindle with a rubber ring, a spring and a plastic button.
- To replace the button, disassemble the gearbox.
- Remove the spindle from the housing.
- Put the spring on the button on the inside.
- Insert the spindle into the gear case from the inside, and the button from the outside. Press until it clicks.
- Assemble the gearbox.
Spindle lock button replacement and gearbox repair
Care and proper operation of the angle grinder
For the angle grinder to work for a long time, follow the rules:
- Watch integrity of isolation of a wire, plug. Do not remove protection.
Lubricate and clean the entire tool.
After turning off the angle grinder, wait until the rotation of the circle stops, then lay it on the ground. When the engine stops, the tool through the ventilation holes sucks together with the air stream particles of earth and other hard fractions that hit the motor windings. As a result, an open or short circuit occurs.
If you are actively using an angle grinder, then you are a good master. It’s not difficult for you to understand the device’s device and repair it with your own hands. First, find the fault and determine which nodes should be checked. Repair the angle grinder carefully, without haste, so that a minor breakdown does not turn into a major one.
Angle grinders (USM, angle grinder) under the German brand Bosch are of high quality, reliability and durability. The main competitive advantage of Bosch angle grinders lies in the widespread use of innovative technologies in the manufacture of the product.
But German quality cannot resist Russian negligence. Improper use of the tool, untimely replacement of grease, carbon brushes, bearings leads to failure of the tool.
In order to repair a Bosch angle grinder, you can go in two ways: give the angle grinder to a service center or repair the Bosch angle grinder with your own hands.
The first option is more expensive and not always high quality. The second option can be implemented only if the consumer has a great desire to figure everything out on his own.
A diagram of the Bosch angle grinder will help you repair yourself.
Bosch angle grinders are conventionally divided into low-power up to 1000 W, and powerful over 1000 W are marked GWS 7-125, GWS 20-230 or others.
The first number of 20 or more indicates a tool power of more than 1000 watts. The second number 230 confirms that this is the maximum diameter of the cutting wheel.
The first digit up to 20 indicates the power of the tool up to 1000 watts, and the second about the maximum diameter of the cutting wheel up to 125 mm.
Design Features of Bosch Angle Grinder
The design feature of the Bosch angle grinder is presented in the gearbox as a thrust bearing of a driven helical gear of a needle bearing. In Bosch rotary hammers, the driven gear is mounted on the spindle shaft by compression.
In Bosch angle grinders of low power, in which spur gears are placed in the gearboxes, the installation of shims is provided. This design allows you to restore the functionality of the contact gears, reducing the thickness of the gasket. Helical gears at high tool speeds wear out significantly less than spur gears.
The working environment of grinders is most often a dusty space. Dust is the main danger leading to failure of the power tool, an amorous and angle grinder.
Repair tool required
To repair a Bosch angle grinder, a tool is indispensable. We’ll make a reservation right away, if you have a screwdriver, this will significantly speed up the process of disassembling and assembling the tool.
But you can get by with a set of screwdrivers, preferably with a ratchet mechanism. You can not do without an open-end wrench, with which you will unscrew the nut securing the leading helical gear.
It is better to have a special puller for dismantling the bearings.
Diagnostics of the electrical part can be carried out using a tester or a short circuit detection device.
It is especially useful in that it allows you to determine the malfunction of the rotor or stator without removing the assembly.
The diagram of the Bosch angle grinder will help you carry out repairs yourself, and these instructions will help you adequately cope with any problem.
DIY disassembling Bosch angle grinder
For the owner of a power tool, knowledge of his device and the ability to disassemble is a must.
Knowing the disassembly procedure, the angle grinder allows you to independently perform such tasks as changing grease, changing bearings and carbon brushes.
To disconnect the gear housing pos. 821 from the stator housing pos. 888, it is necessary to disassemble (remove) the handle housing, angle grinder pos. 24.
This operation must be performed to remove the carbon brushes pos.810 holding the rotor manifold.
In the second stage, unscrew the 4 (four) screws pos. 61 that secure the gear housing and stator.
Having pulled out the rotor together with the gearbox, proceed to disassemble the gearbox.
Repair angle Bosch grinder begins with the disassembly of the gear pos.821. Dismantling of the gearbox starts with unscrewing 4 (four) screws pos. 60. As a rule, the screws are screwed into the sealant at the factory. Will have to make some efforts.
Just note! For Bosch low power grinders, the gearbox uses spur gears. For grinders with a power of more than 1000 watts, helical gears are used in the gearboxes.
How to remove the driven gear
After removing the gearbox cover, you can get the helical gear assembly pos. 26.
To remove the gear, you must use a press or puller. But the use of a puller is difficult, because it requires the use of special thin sponges.
Before removing the helical gear, check the gear backlash, tooth integrity, contact spot.
A bearing pos. 50 is pressed onto the spindle shaft, pos. 26. If the bearing has a large backlash, it is noisy when scrolling, the grease has dried, it is preferable to replace it.
To remove the bearing, it is necessary to remove the gear wheel, circlip and dismantle the bearing. If the bearing remains in the gear housing while removing the rotor shaft assembly, the bearing is removed using a hammer and a soft tip.
How to remove pinion Bosch angle grinder
Leading gear pos. 27 is removed from the rotor shaft in the following sequence:
- Hand tighten the rotor and use the open-end wrench to unscrew the nut pos. 45 counterclockwise;
- Remove the washer pos. 59.;
- Remove the helical gear, key 27.
Check visually the integrity of the gear teeth, contact spot.
If the gears are very worn (licked), there are chipped teeth, then they must be replaced. over, the replacement of gears is always done in pairs.
In low-power Bosch angle grinders, a needle bearing is used as a support bearing in the gearbox.
Do-it-yourself repair of the bosch uhm follow the strictly enclosed instructions. If you need to remove the needle bearing from the housing, quick thinking is indispensable. Its dismantling is carried out only at destruction.
To get the destroyed bearing race, you can use the proven method.
A tap is selected with a diameter slightly larger than the inner diameter of the cage of the destroyed needle bearing. The tap is fixed in the screwdriver’s chuck and screwed carefully at low speeds into the clip. When the tap reaches the bottom of the gear housing, it will begin to raise the clip.
In addition to the spindle shaft needle bearing, Bosch angle grinders also use two more bearings mounted on the rotor shaft.
How to remove bearings from a rotor Bosch angle grinder
To remove the bearings from the rotor, pos. 803, Bosch angle grinders are recommended to use pullers.
The bearing pos.15 near the collector is easily removed, but to remove the bearing pos.14 from the impeller side, it is complicated by the fact that a number of preparatory operations are necessary.
The bearing pos.15 is closed by a soft rubber socket. A similar rubber protection pos.33 also covers the bearing pos.14.
To remove the bearing pos. 14, unscrew the nut pos. 45, remove the spur gear pos. 17 and the plastic protection pos. 33. Using a puller, you can easily remove the bearing from the rotor shaft.
And if there is no puller? A vice, two metal strips and a hammer with a soft metal extension will come to the rescue.
Dismantling Bosch angle grinder
Video: BOSCH GWS 850 CE (angle grinder 125) Which angle grinder to choose Small angle grinder with speed control
Possible electrical problems
Faults in the electrical part of the Bosch angle grinder can be divided into simple and complex.
Simple electrical faults Bosch angle grinder
If you turned on the angle grinder and it refuses to work, start looking for a malfunction with a broken power supply wire. Most often, a wire break appears at the entrance to the angle grinder or to the fork. Avoid twisting; this will cause a short circuit in the tool.
To determine such a malfunction, it is necessary to open the handle covers of the angle grinder. In Bosch angle grinders up to 1000 W, the cover is fastened with one screw at the end. For Bosch grinders over 1000 W, the handle cover is secured with several screws.
Using the tester, ring the power circuits from the input plug, pos. 5, to the switch. With the whole circuit, proceed to check the operation of the switch. Bosch angle grinders use simple switches controlled by a switch lever.
But the electrical contacts of the switch burn up and become the cause of the failure of the angle grinder. It is impractical to restore the contacts of the plastic switch, it is necessary to replace it with a new one.
If the switch is intact, use a tester to check for the presence of a chain from each pin of the plug to each carbon brush. For whole chains, the angle grinder should turn on. If it does not rotate, then the malfunction is mechanical. Jamming of gears or destruction of bearings is possible.
If your Bosch angle grinder is gaining momentum regardless of you, it starts to get very hot, sparkle, you need to pay attention to the integrity of the rotor windings, stator windings.
An involuntary set of revolutions of the ear indicates a malfunction of the stator windings. The integrity of the windings is checked by a tester, and the short circuit between the turns is checked by a special device.
How to identify rotor failure
Rotor repair is a complex process available to foremen with straight arms.
A rotor malfunction is indicated by a drop in engine speed, the appearance of a long sparkling trace on one of the brushes. This is the first sign of a short circuit in the turns of the armature winding.
Repair of the rotor is preferably carried out in special workshops. And you can rewind yourself, if you decide to repair the Bosch angle grinder yourself.
The dark color of the rotor winding and burnt collector lamellas indicate a short circuit in the rotor circuits. The malfunction is eliminated only by replacing with a new rotor.
Bosch angle grinder repair includes stator restoration. The main sign of stator failure is a spontaneous increase in the speed of the working angle grinder, which cannot be reduced by adjustments. A burned stator winding changes color, becomes darker. The stator core also darkens from high temperature.
The stator is easier to rewind, although here you must follow certain rules and sequence.
If you removed the stator housing cover, carefully inspect the condition of the carbon brushes and rotor manifold lamellas.
The length of the carbon brushes should not be less than 8 mm. By the way, in Bosch angle grinders, carbon brushes with a “shot” are used, a device that stops the operation of the angle grinder with a minimum length of the carbon brush.
The collector lamellas must not show any deposits or wear. Carbon deposits are easily removed with cotton wool soaked in alcohol.
Stator overheating and rotor short circuit
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Speed control malfunctions
In angle grinders of the Bosch series, especially of low power, speed controllers are installed. Access to the speed controller is carried out by opening the handle of the stator housing, which is held on one end screw.
The speed range of the controller can be set with a potentiometer hidden in the handle panel.
It is quite easy to remove a faulty regulator, since it is mounted only on the guide.
Repair of the UMM speed controller is a complex process, the implementation of which requires not only special knowledge, but also tools and equipment.
If the speed controller is out of order, but there is no new one, then disconnect the supply wires and install a jumper.
Red shows the jumper installed when the speed regulator fails.
Bosch angle grinder is designed for cutting, grinding, polishing work. The operation of the tool in dust at high loads is particularly detrimental to the durability of the gearbox, namely its gears.
In addition to wear and tear of gear teeth, mechanical failures include the destruction of bearings and the housing. Repair of the Bosch angle grinder in terms of replacing failed bearings and rebuilding the housing is not difficult if there is a desire and need.
Assembly angle grinder
The assembly of the angle grinder begins with the examination of all parts, assemblies, bearings, gears.
Pre-prepare the workplace with proper and good lighting, lay tools, lubricants, wipes.
What grease to use for a Bosch angle grinder
Repair to Bosch ears will not be of high quality if you do not change the grease during its execution. For high-quality lubrication of components, Bosch angle grinder is recommended to use those lubricants that are offered by the tool manufacturer. But their high price makes us look for another way, and there is one.
Domestic lubricant manufacturers have developed special lubricants for gearboxes and grinder assemblies.
In terms of quality, they are in no way inferior to foreign lubricants, but are much cheaper. The only negative, our lubricants require a more frequent change.
And you can use your own grease.
The assembly of the rotor consists in mounting bearings on it, installing the impeller. Lubricated bearings are pressed onto the shaft using a wooden extension. The bearing near the collector is closed with rubber protection. This is a general rotor shaft assembly algorithm.
In some models, the Bosch angle grinder has its own characteristics.
The assembly of the gearbox begins with the installation of a rotor shaft in its housing. When the shaft is inserted into the housing, the drive gear, washer, and lock nut are put on the shaft. The gear housing with the inserted shaft must be placed in the stator housing.
When you insert the collector bearing into the socket, push the gear housing to the stator housing. Check the ease of rotation of the rotor in the bearings.
A spindle assembly with a mounted bearing and gear is mounted in the gear housing cover.
It remains to insert the cover into place and check the quality of rotation of the spindle shaft. If the shaft rotates easily by hand, it is fashionable to tighten the screws securing the rotor housing cover. The screws are pre-lubricated with sealant.
This is a general gearbox assembly algorithm. On some models, the repair of the gearbox Bosch angle grinder is slightly different.
- Knowing the general scheme of Bosch grinders, you can safely take on the dismantling of a tool for lubrication;
- The ability to repair a Bosch angle grinder with your own hands will extend the life of the tool, independently replace the grease, carbon brushes;
- Observing the operating mode and technological maintenance of the tool, you will extend its trouble-free operation for many years.
Good luck in job!
Repair video Bosch angle grinder
Assembling Bosch Angle Grinder
Video: BOSCH GWS 850 CE (angle grinder 125) Which angle grinder to choose Small angle grinder with speed control
How to replace bearings with a Bosch angle grinder
Video: How to replace bearings with a Bosch angle grinder