How to make a speed grinder with your own hands

If you have an old angle grinder in your arsenal, do not rush to write it off. Using a simple electrical circuit, the device can be easily upgraded by adding to it the function of changing the frequency of turns. Thanks to a simple regulator, which can actually be assembled with your own hands in a few hours, the functionality of the device will increase significantly. Reducing the speed, the grinder can be used as a grinding and sharpening machine for various types of materials. There are new opportunities for the use of additional attachments and accessories.

Why low speed grinder?

The integrated disk speed control feature allows you to delicately handle materials such as plastic or wood. At low revs, comfort and safety is increased. This function is especially useful in electrical and radio installation practice, in car-care centers and restoration workshops.

In addition, among professional users of power tools there is a strong opinion that the simpler the device is, the more reliable it is. And additional service "stuffing" is better to bring out of the power unit. In this scenario, the repair of equipment is greatly simplified. Therefore, some companies specifically produce remote individual electronic regulators that are connected to the power cord of the machine.

Speed ​​controller and smooth start-up - what are

for?

Used in electromechanical instruments, the design of which uses a collector motor. Help reduce the wear of the mechanical part of the unit during start-up. Reduces the load on the electrical elements of the mechanism, putting them into work gradually.

As studies of the properties of materials have shown, the most intensive development of friction nodes occurs during an abrupt transition from a state of rest to a fast movement mode. For example, one start of an internal combustion engine in a car is equal in terms of wear of the piston group to 700 km of run.

When the power is turned on, there is an abrupt transition from the state of rest to the rotation of the disk at a speed of 2.5–10 thousand revolutions per minute. Those who worked with the grinder are well aware of the feeling that the machine is simply “breaking free”.It is at this moment that an overwhelming amount of damage occurs associated with the mechanical part of the unit.

The stator and rotor windings are also under pressure. The collector engine starts in short circuit mode, the electromotive force is already pushing the shaft forward, but inertia still does not allow it to rotate. There is a jump start current in the coils of the motor. And although they are constructively designed for such work, sooner or later there comes a moment( for example, during a voltage surge in the network) when the winding insulation does not withstand and an interturn lock occurs.

When the soft start and change engine speed circuits are included in the tool's circuit, all the above problems automatically disappear. Among other things, the problem of the “failure” of voltage in a common network at the time of launching a hand tool is being solved. This means that the refrigerator, television or computer will not be exposed to the danger of "burnout".And the automatic circuit breakers on the meter will not work and turn off the current in the house or apartment.

The soft start scheme is used in the middle and high price grinders, and the speed adjustment unit is mainly used in professional angle grinders.

Speed ​​adjustment allows the grinder to process soft materials, perform fine grinding and polishing - at high speed, wood or paint will simply burn.

Additional wiring diagrams increase the cost of the tool, but increase the service life and safety level at work.

How to assemble a regulator circuit with your own hands

schematic circuit diagram In order to assemble the simplest speed control for the grinder, it is necessary to purchase the parts shown in this diagram.

Schematic diagram of the speed controller

Where:

• R1 - resistor, resistance 4.7 kOhm;
• VR1 - trimming resistor, 500 kΩ;
• C1 - 0.1 μF x 400 V capacitor;
• DIAC - triac( symmetrical thyristor) DB3;
• TRIAC - Triac BT-136/138.

The operation of the circuit

The trimming resistor VR1 changes the charging time of capacitor C1.When voltage is applied to the circuit, at the first moment of time( the first half period of the input sinusoid), the triacs DB3 and TRIAC are closed. The output voltage is zero. Capacitor C1 is charging, the voltage on it increases. At a certain point in time, set by the chain R1-VR1, the voltage on the capacitor exceeds the opening threshold of the triac DB3, the triac opens. The voltage from the capacitor is transmitted to the control electrode of the TRIAC triac, which also opens. Through the open triac current begins to flow. At the beginning of the second half cycle of the sinusoid, the triacs are closed until the capacitor C1 is recharged in the opposite direction. Thus, the output is a pulsed signal of complex shape, the amplitude of which depends on the operating time of the circuit C1-VR1-R1.

Assembly procedure

The assembly of this scheme does not complicate even a beginner radio amateur. Parts are available, you can buy them in any store. Including vypayat from old boards. The order of assembly of the regulator on the thyristors is as follows:

1. An electrical circuit is assembled on a printed circuit board or by an outboard assembly.

   Thyristors are mounted on a copper or aluminum radiator

2. A finished regulator is tested with an incandescent bulb. If everything works correctly, the glow of the light bulb will change in accordance with the rotation of the knob.

   Incandescent lamp 40-60 W smoothly ignites

3. The assembled device is installed directly on the grinder.

   The regulator is mounted in a previously prepared place.

4. If the Bulgarian tests were successful, the speed regulator is fixed and covered with a casing.

How to connect the device to the Bulgarian, options

Connecting the regulator depends on what type of device is selected. If a simple circuit is used, it is sufficient to mount it into the power supply channel of the power tool.

Installing a self-made board

There are no ready-made installation recipes. Everyone who has decided to equip the angle grinder with a regulator disposes it according to its goals and instrument model. Someone inserts the device into the holder's handle, someone into a special additional box on the case.

In different models, the space inside the body of the grinder may be different. Some have enough free space to install the control unit. In others it is necessary to take it to the surface and fix it in another way. But the trick is that, as a rule, there is always a certain cavity in the back of the instrument. It is designed for air circulation and cooling.

Cavity in the back of the device

Usually it is here that the factory speed controller is located. Handmade scheme can be placed in this space. So that the regulator does not burn out, thyristors should be installed on the radiator.

Video: smooth start plus and engine rpm adjustment

Features of mounting the finished block

When you buy and install the factory regulator inside the grinder, you often have to modify the case - cut a hole in it to output the adjustment wheel. But it can adversely affect the stiffness of the casing. Therefore, it is preferable to install the device outside.

The adjustment wheel changes revolutions

The numbers on the adjustment wheel indicate the number of revolutions of the spindle. Value is not absolute, but conditional."1" - the minimum speed, "9" - the maximum. The remaining figures are used for orientation in the regulation. The location of the wheel on the body is different. For example, on the Bosch PWS 1300–125 CE, Wortex AG 1213–1 E or Watt WWS-900, it is located at the base of the handle. In other models, such as the Makita 9565 CVL, the adjustment wheel is located at the end of the casing.

The connection of the regulator to the grinder is not complicated, but sometimes it is not so easy to stretch the cables to the button, which is located on the other end of the device. The problem can be solved by selecting the optimal cross-section of the wire or bringing it to the surface of the casing.

The regulator is connected according to the

scheme. A good option is to install the regulator on the surface of the device or to attach it to the network cable. Not always everything turns out from the first attempt, sometimes the device has to be tested, and then make some corrections. And this is easier to do when access to its elements is open.

Important! If there is no experience with electrical circuits, it is more expedient to purchase a ready-made factory regulator or LBM equipped with this function.

Fixing to the power cord

The user manual for the device

The basic rule when operating a grinder with a homemade speed control is the observance of work and rest. The fact is that an engine operating on “regulated” voltage is especially hot. When grinding at low revs, it is important to take frequent breaks so that the collector windings do not burn out.

It is also highly recommended not to turn on the tool if the speed regulator is set to minimum - the undervoltage is not enough to rotate the rotor, the collector lamellae will remain in short circuit mode, the windings will start to overheat. Unscrew the variable resistor to the maximum, then turn on the angle grinder, reduce the speed to the desired value.

Observance of the correct order of inclusion and adjustment will allow the grinder to operate for an unlimited time.

In addition, it should be understood that the speed adjustment on the grinder is based on the principle of a water tap. The device does not increase the number of revolutions, it can only lower them. From this it follows that if the maximum passport speed is 3000 rpm, then when the speed controller is connected, the Bulgarian will work in the range lower than the maximum speed.

Warning! If the angle grinder already contains electronic circuits, for example, it is already equipped with a speed controller, then the thyristor controller will not work. The internal circuits of the device simply will not turn on.

Video: self-made regulator of turns of LBM

Equipping the grinder with the engine speed control circuit will increase the efficiency of the device use.and expand its functional range. It will also save the technological resource of the grinding machine and increase its service life.

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