Reverse does not work on the screwdriver

Breakdowns in the electrical part

In the wiring diagram of a screwdriver, batteries often fail, the second place is shared between buttons and the engine, in which the brushes most often deteriorate.

reverse, does, work, screwdriver

Elimination of breakdowns in the mechanical part

Here, most of the faults are obvious, in contrast to the electrical part. But this does not mean that they are easy to eliminate. Special tools and skills may be required. But in some cases, the owners can cope on their own.

The ratchet does not work

The ratchet, as the torque limiter is easily called, plays an important role in the screwdriver, therefore it must always work properly. Its device consists of a toothed coupling half that holds the gearbox relative to its housing, and a second coupling half of balls supported by an adjustable spring.

The greater the force of the regulating spring on the balls in the housing, the more the toothed sleeve is kept from turning. If the braking torque exceeds the resistance torque of the clutch, the balls begin to roll over the teeth and thus the torque is limited. The spring force regulator has a scale on the outside in Newtons.

In this unit, the wear of the “crown” is often observed. the teeth of the bushing are ground with balls and the tightening torque of the screwdriver not only does not correspond to the scale, but itself becomes completely insufficient. The same happens if the regulating spring breaks. Malfunctions are eliminated only by replacing parts with new and completely similar ones.

Frequent malfunctions

The weak point of the screwdriver is the gearbox.

To ensure the maximum compactness of the tool, the design contains a two-stage planetary gearbox, in which the motor shaft and the working body (chuck) are coaxial.

Most often, small gears (satellites) are rolled in the first stage of the gearbox. They do not have the greatest force in the mechanism, and therefore manufacturers often make them from durable plastics in cheap household tools. It is not uncommon for the stop clutch to wear out when the ratchet is overused. Worn gearbox shaft bearing leads to radial runout.

Electrical faults most often occur when brushes are worn out, especially among builders, who do not protect the screwdriver from stone dust getting inside. It washes the brushes very quickly and damages the motor manifold. In the motor itself, short circuits are possible between the turns, which sharply reduce the efficiency of the engine and quickly disable it.

The speed control button and reverse switch are also afraid of dust and rough impact: shock, strong pressure, etc. As a result, they quickly fail.

Batteries often “let down” the users of the tool, or rather, it would be better to say that the users themselves violate their operating conditions. The diametrical difference between lithium-ion and nickel-cadmium batteries turns out to be especially insidious: the former must be recharged as often as possible, and the latter, on the contrary, must be completely discharged before the next charge. Consumers who do not delve into these subtleties, carelessly study the instructions, learn from their mistakes. Let’s take a closer look at why the screwdriver does not work, and how to eliminate this reason.

Cartridge

Keyless chucks are usually used in screwdrivers. The chuck of the screwdriver contains jaws that are tightened with a threaded cone in the direction of the axis and hold the shank of the replacement tool. These jaws move along the threads on the taper and are held in the bushing grooves. As a result of the ingress of dirt, abrasive and poor lubrication, the rubbing surfaces of the jaws and the cone wear out. These details have to be changed.

In order to disassemble and repair the cartridge, pullers may be needed to press its parts out of the body. It is not recommended to knock them out with a hammer due to the risk of breakage of some parts.

Engine

The screwdriver motor can be assembled entirely in a metal case.

In this case, it has a magnet instead of a stator field winding.

This slightly increases its reliability, but can be a significant hindrance during repairs.

Such engines are often made non-separable and not repairable. Plain bearings are used in such motors. If it is possible to disassemble a motor of this type, then the armature can be rewound or brushes replaced.

In the case when the motor has a stator winding, the screwdriver body itself serves as its housing and bearing shields. These motors use permanently lubricated rolling bearings designed for the entire service life. Sometimes you have to change them. Sometimes the fan impeller breaks from foreign objects entering the ventilation slots.

Often it is necessary to rewind the stator or rotor of the motor along with replacing the insulation in the grooves, replace worn brushes or grind a collector with a worn surface.

Replacing brushes

Brush replacement is done quite often, especially for screwdrivers used by builders and fitters who work with stone or near a stone dust source. For example, it is enough to assemble a wooden rack in a warehouse with cement with a screwdriver so that the brushes are almost half worn out.

To replace the brushes, you need to disassemble the screwdriver, remove the motor and then remove the brushes. How this is done depends on the design of the engine. Sometimes the brushes are fixed with plugs (this is the easiest case to replace them), and sometimes they are pushed out towards the collector axis. In some cases, it is necessary to resort to devices to temporarily hold the brushes during assembly.

Button problems

Buttons can break with brute force. Often splinters, small fragments of metal from self-tapping screws, or sheet metal that stick to the worker’s hands get inside. This debris leads to jamming of the button, and if it is not removed in time, it easily bores the plastic case in which the button with a regulator is mounted.

As a result, the instability of the regulator begins, the speed jerks of the screwdriver and in the end it completely fails. The same applies to the reverse derailleur if it is poorly designed to protect it from dust.

Repair of these parts is not always possible, it again depends on the specific version of the button assembly. Most often, you have to change the entire node to a new one. Electrical faults can be eliminated by replacing parts.

The principle of operation of a screwdriver from A to Z we understand how the tool works

Cordless-type models are popular, therefore, using their example, we will analyze the principle of operation of screwdrivers. Knowing the device and design of the screwdriver, it will not be difficult to find out how this device works. However, even experienced craftsmen often stumble when answering questions. what is the ratchet for, how the button works, and why planetary gearboxes are used on screwdrivers, and not ordinary ones. Consider the detailed principle of operation of the screwdriver, and find out all the answers.

  • The device starts working when you press a button, which is also called a switch. However, switches (do not have a speed control option) are usually used on angle grinders, and on screwdrivers, buttons with a built-in speed control are used. The principle of operation of the regulator is simple. the stronger the pulling force on the trigger, the higher the rotation speed of the chuck.
  • In order for the cartridge to begin to rotate when the start button is pressed, it is necessary to provide a direct current supply to the electric motor. For this, a battery is used, which acts as source. It consists of a set of cans that are connected in series, which together allows you to receive a voltage from 9 to 24V
  • The battery for screwdrivers is removable, which allows not only recharging it, but also changing it when it is discharged. From the battery, the current is supplied to the power button. If the battery is discharged or deteriorated, the screwdriver can operate from a car battery
  • The button has a complex non-separable design. The contacts are closed in the button, and the polarity of the voltage supplied to the contacts of the electric motor changes
  • Two wires from the battery are connected to the button, which are closed, and go to the contacts of the collector DC motor. There is an element in the design of the button that is responsible for adjusting the rotation of the cartridge depending on the force of pressing the trigger. the so-called soft start
  • A direct current is supplied to the collector motor, which is fed to the rotor winding. The role of the stator in the motor is played by permanent magnets, through which the rotor rotates. A gear is attached to the rotor shaft, the torque from which is transmitted to the gearbox
  • The planetary gearbox on the screwdriver consists of a set of gears with internal and external links. By means of gears, torque is transmitted from the engine to the tool chuck
  • The gearbox is connected to the shaft on which the chuck is attached. In the jaws of the collet device, a working nozzle is fixed. a drill, a bit and others
  • In addition to these elements, the design of the screwdriver has a ratchet or a clamping force regulator with a safety clutch
  • The overload clutch prevents the shaft from seizing, for example when drilling or screwing in a screw. The absence of a safety clutch contributes to the fact that the rotor winding can burn out due to an increase in the load
  • The torque force regulator serves to ensure an effective effect on the treated surfaces. It eliminates the rotation of the chuck relative to the shaft, eliminating the increase in load. The presence of the regulator allows you to screw the fasteners with a certain moment
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All these devices are part of the screwdriver. Let us consider in detail each element of the tool, as well as its design features, which will allow us to understand the question of how the screwdriver works. The video below shows a detailed principle of operation of a screwdriver drill.

How a screwdriver works and tool design. what you need to know when using

It’s hard to imagine a home craftsman’s arsenal without a screwdriver. This tool is capable of replacing screwdrivers, wrenches and drills. Structurally, it consists of two main parts. electrical and mechanical, through which useful work is performed. Many owners do not know all of its capabilities, and even more so how a screwdriver works. It is in the question of the principle of operation that it is necessary to understand in detail in order not only to assess the capabilities of the device, but also to facilitate the implementation of its repair.

Screwdriver button working principle and design

Battery voltage is supplied to the engine through a button. The button is used not only as a contact closure device.

The button has the following tasks:

  • Closing the contacts of the wires “plus” and “minus”, due to which power is supplied to the engine
  • Reverse. change the polarity of the contacts of the wires entering the engine. This allows the rotation of the motor shaft in different directions.
  • Adjustment of speed depending on the force of pressing the start button
reverse, does, work, screwdriver

The function of the button is to provide smooth voltage to the tool motor when the trigger is pulled.

How does the battery work on self-contained screwdrivers

The battery is the source through which the electric motor is driven. The battery design uses cylindrical cans made of nickel-cadmium or lithium-ion filling (there are also metal-hydride cans). Each jar produces a voltage of 1.5 to 4 volts, depending on the type of filling. Each bank is connected in series with each other, therefore, as a result, the voltage of each bank is summed up. This voltage is transmitted through the contacts to the instrument.

Depending on the number of cans inside the screwdriver battery, the batteries are capable of delivering voltages from 9 to 24V. The most popular are 12V-14V models. Low-power ones are 9-volt screwdrivers, and high-power ones include devices with a supply voltage from 18V to 24V. In addition to voltage, batteries have another important parameter. this is their capacity. Capacity is the amount of charge that a battery is capable of delivering over a corresponding period of time. The larger the capacity, the longer the screwdriver can work without recharging. To charge the battery, special chargers are used, the principle of operation of which must be considered.

How a screwdriver gearbox works

The planetary gear mechanism is designed to reduce the rotation speed and increase the torque. The reducer consists of a set of gears. They have a different number of teeth, due to which the rotation speed is reduced to the corresponding values.

The design of screwdrivers has switches designed to operate the tool at different speeds:

  • The first is slow, used for screwing self-tapping screws, screws, as well as threaded connections
  • The second one is fast, when the tool is turned on in the “2” mode, the chuck rotates at a speed 2 times faster than at 1 speed. In this mode, the device is used for drilling metal and wood. It is possible to drill concrete with a screwdriver only if it has an impact mode. Typically, these are network-type impact drills with high power.

The reducer consists of driving and driven links. gears. The driving gears are called the “sun” and the driven gears are called the carrier. The speed is regulated by mechanically shifting gears with a large number of teeth to a small one. As a result, the tool is able to work in two modes. drilling and screwing.

The motor on a screwdriver and how it works

The principle of operation of a brushed motor and a brushless (brushless) motor is different. The most popular motors on screwdrivers are of the collector type. Their advantage is their low cost, and the disadvantage of having a consumable element is brushes. Over time, during the operation of the device, the brushes wear out, so at one moment you can find out that the motor stops working. Often, such a breakdown is perceived by the owner of the tool as burning out the rotor winding, however, it is enough to replace the brushes or clean (usually copper) for the device to resume its work. Graphite or carbon brushes are used on corded power tools.

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In a collector motor, current is applied to the rotor winding through the brush assembly. When a current flows, an electromotive force is induced, thereby the rotor turns from a winding into a magnet. A stator in the form of two magnet plates is located around the rotor. The opposition of two magnets (rotor and stator) contributes to the repulsive force, which ultimately leads to the fact that the rotor begins to rotate. The rotational force is used for useful purposes to propel a tool holder with working attachments. This is how all collector motors work, both network and battery types. The only difference between them is that on network devices, the motor consists of a stator and a rotor with windings.

The principle of operation of a brushless motor differs in that the shaft is connected to the stator. The stator is made up of magnets and is driven. The rotor then stands still and is supplied with current directly without brushes. An EMF is induced in the rotor winding, and now, by means of the reaction force, the moving element, the stator, rotates. A brushless motor is more reliable and efficient, since there are no consumable elements (brushes) in it, which means that it is able to work long enough until the winding burns out. They have a drawback. it is high cost. Below is a diagram of how a brushless motor works on a screwdriver.

The high cost of brushless screwdriver motors lies in the complexity of their design. To ensure the rotation of the stator from the magnets, not two, but three wires should be connected to the rotor winding. This is necessary to ensure the phase-shifting effect, through which the EMF is induced. To achieve this effect, special devices are used that provide a voltage supply with a phase shift.

The principle of operation of the cartridge

Chucks on screwdrivers are of two types. keyless and key. Keyless clamps are more popular, and they come in one and two clutches. Key ones are more reliable, since they exclude the possibility of turning the nozzle. Key executive bodies are usually used on drills, which exclude the rotation of drills with cylindrical shanks. On screwdrivers, quick-clamping is usually used, since they quite reliably fix the nozzles in the form of bits with a hexagonal shank design.

Key and keyless chucks on screwdrivers have a similar design and principle of operation, which is based on the movement of the clamping jaws. The design has three jaws, which fix the shanks of the working nozzles. drills, bits, polishing nozzles, etc.

In order for the cartridge to serve for a long time, it is necessary to periodically introduce lubricants inside, and also to clean the working bodies from clogging. If the jaws fail, they cannot be replaced. When choosing a cartridge, it must be borne in mind that they differ in such a parameter as the diameter of the nozzle shanks that can be fixed in it. It is also necessary to take into account the diameter of the hole for fastening to the screwdriver.

The chuck is attached to the screwdriver with two threaded clamps. The first clamp is located inside, and is presented in the form of a four-sided (less often one-sided) screw, which has a left-hand thread. To unscrew it, you must turn it to the right. After unscrewing the screw, it is necessary to unscrew the element itself, which is attached to the shaft.

The principle of operation of a screwdriver is simple and uncomplicated, but everyone who plans to repair, alter, modernize, etc. should figure it out. Knowing the principle of operation of screwdrivers and wrenches, you can eliminate any breakdowns of these devices, and return the tool to working condition.

Screwdriver button repair. instructions and diagram

The screwdriver is a mobile tool that makes it easier to work with fasteners and screw connections.

Until recently, cordless screwdrivers could only be found in the arsenal of professionals, but with the advent of inexpensive household models on the wide sale, their popularity has sharply increased.

Unlike an expensive professional tool, budget counterparts have a smaller resource, which is why they are more likely to fail.

One of the weakest points of a household screwdriver is the start button and reverse switch. As practice shows, it is they who break most often.

As a rule, it all starts with the fact that the soft start function stops working, then a stronger pull on the “trigger” is required to start the electric motor.

Over time, the tool ceases to respond to any manipulation altogether. Often there is a problem of the opposite nature, when the motor starts to work spontaneously.

In some cases, to eliminate the defect, it is enough to disassemble the tool and clean it, although more often a complete replacement of the screwdriver button is required. In both the first and second cases, you can fix the problem yourself. Everything in order.

Device and diagram of the screwdriver button

The screwdriver button is the main control element that performs several functions at once:

  • Turn on / turn on the instrument;
  • Switching the direction of rotation;
  • Smooth engine start;
  • Speed ​​control.

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In this case, each of the controls built into the button block cannot work correctly by itself. Except for the direction of rotation switch, which is more often a separate function block.

In most cases, the body consists of three conventional compartments, in which the working units and mechanisms are located.

  • In the lower part of the body there is an on / off control unit and an electric motor speed adjustment.
  • In the middle part is the “trigger” of the soft start (the deeper you press it, the higher the rotation speed of the cartridge). When pressed, the button slides in a special block along the guides, a variable resistor is responsible for adjusting the speed.
  • In the upper part there is a reverse button. a switch for the direction of rotation of the cartridge. The direction is reversed by reversing the polarity of the voltage applied to the switch.

This is approximately how all control units of screwdrivers of different brands are arranged. To get acquainted with the device of the button of a specific model of the tool in more detail, we recommend that you study the diagram of the screwdriver button (it is in the instructions).

How to repair a screwdriver button if it does not work. detailed instructions

To diagnose and repair a screwdriver, you will need the following tools:

  • Crosshead screwdriver;
  • Narrow flat blade screwdriver.

As a result of active use of any power tool, dirt will inevitably accumulate inside its body.

Getting into the control unit, it prevents the full movement of the “trigger” and blocks it.

Diagnostic steps:
  • We disassemble the tool body. To do this, disconnect the battery, unscrew all the screws (they can be hidden behind decorative overlays, which will have to be removed).
  • We check the serviceability of the electric motor. To do this, disconnect two power wires from the control unit and connect them to the battery contacts (the engine should start working).
  • We disassemble the screwdriver button. To do this, squeeze the plastic latches and separate the two parts of the button housing.
  • We make a visual inspection of the state of the button for dirt and damage.
  • Next, you need to carefully assemble the screwdriver button, install it in place and test.
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VIDEO INSTRUCTION
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If cleaning the control unit did not work, it is necessary to replace the entire button unit.

For this you need:

  • Disassemble the screwdriver (the process is described above);
  • Install the new button in place of the old one;
  • Connect the motor to the button terminals (polarity is not necessary in this case);
  • Assemble the screwdriver by carefully placing the wires in the case.

It is very important to choose a button for a specific model of a screwdriver, because with all the external similarity and visual correspondence, the part may not fit into the grooves. Typically, new buttons are sold complete with battery terminals and transistor.

DIY screwdriver repair

About the screwdriver device, read the article Screwdriver device.

The screwdriver may not turn on for three main reasons: the battery is faulty (not charged), the power button is faulty, the engine brushes are worn out, or the anchor itself burned out (very rare).

Battery. The battery is checked by a simple measurement at its DC voltage terminals with any tester. The output voltage of a working charged battery must correspond to that indicated on the case. 12V, 18V, etc. Otherwise, the battery must be replaced. The charger of the screwdriver may also be faulty.

Regulator of turns and reverse. The screwdriver speed controller is checked with a multimeter in the continuity mode. It should be noted that if the button is fully pressed, the contacts are closed in it and the voltage is supplied to the engine (to reverse) directly, excluding the speed regulator circuit. Two wires from the battery come to the button, after which two wires are connected to the engine through the reverse contacts. The power button may still have three wires for connecting a regulating element (field-effect transistor), which is placed outside the body. For continuity, the probes are connected to the input and one of the engine wires (if possible, to the reverse input contacts) alternately, then the button is pressed all the way. The device shows the presence or absence of contact, after which the second input wire is measured. We translate the reverse lever and repeat the measurements. If there is no contact, the button changes.

Do-it-yourself screwdriver button repair is possible, but only if you have certain skills. It is important to understand that after opening the case, many switching parts will simply fall out of the case. This can be prevented only by smoothly lifting the lid initially and the desired sketch of the location of the contacts and springs. If darkened contacts are found, they are cleaned with sandpaper. After assembly, repeated measurements are taken and if the results are positive (there is a contact), the button is installed in its original place.

Fixing A Makita Impact Driver With No Reverse

It should be noted right away that if, after repairing the button, the screwdriver motor starts working when the button is fully pressed, and when the button is pressed smoothly, the speed adjustment does not occur, then the reason should be sought in the adjustment scheme. Most screwdriver repairs in this case come down to replacing the entire button.

If there is no reverse, you must replace the reverse switch or try to repair it. To do this, open the switch cover and, as is the case with the button, gently lift it. We check contacts, clean and collect. If the contacts are burnt or deformed, the reverse must be replaced. There are variants of buttons, in which the reverse is assembled inside the button body, in this case the button changes entirely.

If, when the button is released, the engine continues to rotate, and before it did not rotate, in this case it is necessary to pay attention to the speed regulator, namely, to the regulating transistor. It is necessary to replace either the entire button, or separately the transistor.

Electric motor. If all of the above operations have shown the health of the elements, then it is necessary to check the condition of the engine brushes. To do this, the motor is disconnected from the button, and the multimeter probes are connected to the motor wires. The absence of a small resistance in the chain indicates wear on the brushes, but an armature breakage (winding breakage) should not be ruled out, although this happens very rarely. Usually, in this case, the engine changes entirely, but if the brushes are worn out, it is possible to restore the screwdriver motor on its own. On some motors, the brushes can be replaced without disassembling the motor. For others, it is necessary to separate the rear motor cover with brushes from the motor housing.

To do this, it is necessary to bend the rolling of the cover, but in such a way that the edges do not break off, since they will need to be returned to their place after assembly. The flexible wire of the brushes is connected to the holder using spot welding, but the wires of new brushes can be soldered, but only with refractory solder, for example, POS-60. Before assembling the motor, the brushes are removed in the brush holder with a clip made of thin wire, the cover is put in place and the wires are pulled out, thereby freeing the brushes. Next, go around the edges of the case to firmly press the back cover.

Extraneous whistles and squeaks during the operation of the screwdriver can be caused by wear of the armature bushings or a detached magnet that comes into contact with the armature. In the first case, you can extend the life of the engine by dripping a drop of precision instrument oil onto the bushings and then turning on the engine so that the oil is dispersed through the bushings themselves. This method can only extend the life of the engine, but over time you will still have to replace it.

Reducer. From the long operation of the screwdriver under heavy loads and with lateral pressure, the gearbox shaft is bent, on which the cartridge is screwed, a strong runout appears when the screwdriver is operating. The bearing bush or bearing of this shaft can also wear out. If only the bushing or bearing is damaged, and the shaft is not bent, then you can try to replace only the worn parts.

It may happen that the engine starts up for a split second and stops abruptly. Everything points to a breakdown in the gearbox, usually a breakage of the pin on which the satellite is attached. You can try to replace the carrier or the entire gearbox. Failure of the gearbox often occurs due to wear of the gear teeth. A detailed description of the screwdriver gearbox device read here.