How a screwdriver works - its components and cross-sectional design

November 14, 2015 Hand-held power tools, electric-pneumatic tools

Screwdrivers are equally actively used by owners of country houses and owners of city apartments, since they are truly a universal and irreplaceable tool. Professional builders also constantly use this tool in their work, which facilitates the monotonous actions of tightening/unscrewing nuts, screwing in screws, and drilling holes. Using screwdrivers, sheet and panel finishing materials are attached to bases, furniture is assembled, metal, plastic or wood is drilled, and minor repairs are performed.

General view of the screwdriver

Screwdrivers can be corded or corded. The difference between them is the power source. The shape of the tool is similar to a pistol. The screwdriver design and general view are shown in the photo.

A screwdriver is structurally similar to an electric drill and consists of the following components:

• a body that smoothly turns into a handle and a support leg to which the battery is attached and there is a cavity - a block for storing bits.
• Control buttons;
• Battery or power cord.

Screwdrivers with different types of power

During construction, it is often necessary to carry out installation work in places with no accessible electrical networks, so manufacturers produce screwdrivers equipped with batteries. They make it possible to work at height, not to depend on whether the object under construction or repair is connected to the power grid, and not to move a long and heavy inconvenient cable behind you.

Cordless screwdrivers

Screwdrivers are equipped with batteries of various types, including:

• nickel-cadmium batteries, which last up to one thousand charge/discharge cycles;
• nickel-metal-hybrid, with a number of cycles of 500 charges/discharges. The disadvantages include the impossibility of their operation at sub-zero temperatures;
• Lithium-ion batteries that do not have a memory effect, which allows you to charge the tool at any level of battery depletion. These power supply devices are the most environmentally friendly among analogues. To speed up work, replaceable power devices are used.

It is also important that cordless screwdrivers are much lighter than corded ones, especially tools with small lithium-ion power devices.

Cordless screwdriver

The cost of a cordless screwdriver includes the considerable cost of the power supply, which is almost equal to the cost of the tool itself.

Mains powered screwdrivers

Corded electric screwdriver

Networked tools are more reliable, stable and trouble-free in operation, although the trailing cord is inconvenient to operate the device, limiting the movement of the worker. The network tool is used mainly when performing internal installation work or assembling furniture. Corded screwdrivers have more powerful electric motors, are durable and suitable for long-term continuous operation. These devices have a very useful hammer drilling function, which is useful when drilling into brick or concrete walls.

Screwdriver body

The power tool is “packaged” in a plastic case, a material with the following advantages:

1. Plastic serves as a natural insulator from electricity; it does not conduct electricity. Therefore, it is safe.
2. It is lighter than metal, and thus reduces the weight of the tool.
3. And finally, in production, plastic is easier to shape into the desired shape than metal.

The body is conventionally divided into three parts. All rotating mechanisms are located in the upper part. The handle is equipped with soft pads. The master holds the tool with it while working. The pads reduce shock absorption, making work more comfortable and easier. The lower part, the support, inside of which there is a compartment for storing bits.

Corded screwdriver Bosch GSR 6-25 TE 2011 Case: high-power device

This device is distinguished by the presence of a powerful engine and a rich set of equipment. A wired model from a well-known German brand is most often purchased for professional use, but it can also be purchased for home use.

The use of such a device allows you to perform work of any complexity. With the GSR 6-25 TE 2011 Case you can screw in long metal products. When answering the question about which corded screwdriver is the best inexpensive one, this model should not be taken into account. The cost of a German device is significantly higher than the price of domestic analogues.

The engine power in this case is 701 W. The maximum rotation speed of the working tool is 2500 rpm. This device includes in its design a special cartridge, the configuration of which does not require tightening when installing tips. The auxiliary functions of the screwdriver are very extensive. Of these, it is worth highlighting the following: reverse rotation, locking the “Start” key, as well as the presence of a magnetized bit holder.

Electric drill/driver Bosch GSR 6-25 TE 2011 Case has high power

If we take into account all the characteristics of such a device, it is worth noting that it resembles the previous device. The Bosch electric drill/driver also has some disadvantages. The main disadvantage of the device is its large mass. It is also worth saying that the process of changing tips is quite labor-intensive. Otherwise, reviews about this device are mostly positive.

Trigger switch and LED lighting

The trigger switch is located between the top of the housing and the handle. It is located under the master’s index finger, and it is convenient to use it to put the tool into operation. The trigger button closes the electrical network of the screwdriver and starts the electrical mechanisms.

The photo shows the device of the trigger button.

Some models of screwdrivers have built-in LED lighting that illuminates the work area. This is prudent and convenient, since in dimly lit areas it can be difficult to see the screw slot. In the model shown in the picture, the backlight is located in the lower part of the body above the trigger; in some Western European models it is located on the leg above the battery.

Specifications

According to their performance characteristics, screwdrivers for household and professional use are distinguished. For household models, the torque is no more than 15 Newtons/meter, for more powerful and reliable professional tools - approximately 130 Newtons/meter. Professional screwdrivers can also carry out high-quality drilling, which is achieved at speeds of up to 1300 rpm, which the spindles of these devices have. Screwdriver spindles for household use reach a rotation speed of no more than 600 revolutions, and their main advantages are low price, attractive design and the possibility of long-term storage.

Household and professional cordless devices also differ in recharging time: batteries for tools for professional work are charged on average in 1 hour, and for household ones - within seven hours.

The number of tool adjustments also varies: from 5 for household models to 22 for professional models. Some models of screwdrivers are equipped with backlighting, automatic supply of hardware, and the ability to switch between modes - impact or pulse.

Speed ​​control unit and speed switch

The rotation speed and reverse (rotation direction) control unit is connected to a PWM controller, a multi-channel single-pole transistor and a variable resistor, which are hidden in the switch block.

To change the direction of rotation, a changeover contact is used, to which a reverse switch is connected, located above the trigger at the bottom of the screwdriver. It is connected to a changeover contact, which changes the polarity of the voltage supplied to the electric motor. Thanks to this, the direction of rotation changes, which allows screws, self-tapping screws, and screws to be screwed in and out.

Another button is a gearbox speed switch which changes the rotation speed of the chuck. This occurs due to the fact that when the speed button is turned from one mode to another, the bracket (rocker arm) comes into motion, moving the gearbox gear from one level to another.

Operating principle and main components

Before you start repairing a screwdriver with your own hands, you need to understand the principle of its operation and what parts it consists of. The main difference between a screwdriver and other power tools is the use of a mechanism that stops the rotation of the working part of the device. This happens when the maximum resistance configured for the instrument is reached. This value is not constant and can be adjusted. There are two types of device:

• operating from a 220 volt network;
• using a rechargeable battery.

Regardless of the type of device, their operating principle is the same and is based on the transmission of torque. It determines which fastening tool the screwdriver can tighten. To increase torque, devices use gearboxes with a large gear ratio, but the rotation speed is reduced. For screwdrivers operating on AC power, the torque value is related to the power consumption of the tool. The main parts underlying the device of a screwdriver, be it Makita, Hitachi or Bison, are as follows:

• electric motor;
• push button;
• speed controller with reverse;
• chuck;
• the electronic unit;
• gearbox

The electric motor rotates the spindle at a set speed using a planetary gearbox. The torque is controlled by a clutch, and a chuck or hex holder is placed on the spindle. A replaceable device called a “bit” is installed in this cartridge. The screwdriver is controlled by an electronic circuit and reverse switching .

Reverse occurs by changing the polarity of the power supply. The motor is a single-phase continuous current commutator motor. This motor is designed to be connected to an alternating current network. The field winding is connected in series with the armature winding and is divided into two parts. One turns on before the anchor, and the other after it.

The tool uses a planetary type gearbox. The gearbox includes sun and ring gears, satellites, and carrier. The electric motor shaft rotates the sun gear, which transmits torque to the satellites, and they directly affect the carrier.

The gearbox is available in one- and two-stage types. In the second case, a double carrier connected to the shaft is used. The design of two carriers and satellites is located in the middle of the ring gear. It is fixed through special grooves on the body. Along the entire perimeter, the lugs of the ring gear rest against spring-loaded balls through the ring. The load control mechanism acts on the ring through a controlled spring, the force of which is changed by moving the regulator.

Speed ​​control is performed using a pulse circuit assembled on a pulse-width modulation (PWM) chip. The controller controls a field-effect transistor operating in switch mode. The pulse frequency is changed using a variable resistor. The resistance value of the resistor depends on the force applied to the button.

The screwdriver clutch is a ratchet. If the load on the cartridge exceeds the permissible value, the load regulator is activated. The spring force becomes insufficient to hold the ring gear, and it comes off the balls. The electric motor begins to rotate the gear idle. When switching to electric drill mode, this gear is turned off and does not participate in the work .

A rechargeable battery with a voltage of 12 V or 18 V is most often used as a power source. It characterizes the power of the device.

The battery consists of several elements installed in one housing and connected in series. The case has a special latch that allows you to quickly remove the battery.

Chuck with locking mechanism

A planetary gearbox transmits torque to a shaft onto which a self-centering chuck with attachments or bits inserted into it is screwed. The quick-release chuck ensures the fixation of screwdriver and drill bits; it consists of a holder, inside of which there is a clamping sleeve with movable jaws.

The shaft to which the chuck is screwed is equipped with a locking mechanism, which consists of an outer and inner housing and rollers installed between the housings and preventing rotation.

Cartridge

The mechanical part of the tool, designed to attach attachments and transmit rotational motion to them.
Usually installed on the threaded part of the spindle. Can be secured with a screw, clamp or ratchet. High-quality models have a lock that allows you to clamp a drill or bit without additional twisting. Almost all modern screwdrivers in the professional and amateur segment are equipped with a three-jaw self-clamping chuck with self-centering. This allows you to quickly change attachments and securely attach them for long and intensive work. Inside the chuck there is a hexagonal hole for fixing the shank of the nozzle. Usually the attachment occurs between all three cams by slightly rotating the coupling.

To install the nozzle, you need to grab the lower coupling and start turning the upper one - this allows the cams to unclench. To speed up the process, you can fix the nozzle by holding the upper coupling and pressing the start button to clamp, the reverse button to release.

Important! Some manufacturers equip the screwdriver with a magnetic holder for bits without mechanical elements. It is convenient to install a screw depth limiter on such a chuck, but with frequent and intense loads, play appears.

Rechargeable battery with locking button

Since the screwdriver can be cordless and wired, the power supply system in them is different. The cordless screwdriver has a built-in rechargeable battery, which is a device with built-in external contacts for transmitting electricity. The main element of the battery is its power supplies connected in series. Otherwise they are called banks, sample in the photo.

It also has a thermostat that protects the battery from overheating when charging. The rechargeable battery is a removable device, since it must be replaced as the resource is exhausted. The battery is attached to the screwdriver with a locking button, which is located on the side in some models, and in the front in others. From the handle extend contact plates that connect to the battery and provide power.

Speed ​​controller: nuances

Capabilities of household screwdrivers.

The speed regulator is also made according to a very simple scheme. This involves a pulse-width controller and a switch, which is based on a field-effect transistor. As for control, a variable resistor is used here. Its resistance, and therefore the speed of rotation, directly depends on the force of pressing the power button. It is also sometimes called the trigger. Reversing only affects the direction of the voltage applied to the motor. Here, special changeover contacts are used for these purposes. The entire process is automated, so a person does not have to do anything manually.

This is interesting: How to check a screwdriver battery with a multimeter and tester

Engine

Now let's look inside the screwdriver body. The photo shows a cutaway screwdriver, or rather, with the cover removed.

A DC motor converts electrical current into mechanical energy, causing machinery to rotate. This is what the electric motor looks like in some power tools.

An electric motor consists of a stationary stator and a rotating rotor. The stator is a cylindrical metal casing with permanent magnets built around its walls.

Inside the housing there is a rotating rotor. It consists of a shaft on which a core is attached, which is a connection of plates made of high-tech steel, in the grooves of which winding turns of special copper wire are laid. When electrical energy is supplied, the rotor begins to rotate under the influence of these magnets and, through a gear pressed onto the shaft, transmits rotation to the planetary gearbox.

The circuit is connected to the motor through a brush mechanism consisting of two graphite brushes located opposite each other. During operation, the graphite brushes are gradually worn out, but pressure springs ensure their contact with the commutator.

Brushes are consumable parts and if the engine does not start, they are the first thing to check. The impeller serves to remove hot air and cool the engine. In the housing, opposite the impeller, there is a radiator grille.

Corded screwdriver Zubr ZSSh-300-2: the best combination of cost and power

This is a domestic device that has good power (300 W). The length of the cable in this case is a significant advantage. The device has a five-meter cord, which allows you to perform work at a considerable distance from the outlet. The device’s motor provides high torque when drilling and screwing, namely 35 N/m.

Helpful information! The cable of the device is covered with a layer of special frost-resistant rubber, which allows the device to be used outdoors in the winter season.

The maximum idle speed can reach 1400 rpm. The screwdriver of this series has two speed modes, which increases the scope of its application. Many users choose this particular model for home use.

Drill-drivers from the Zubr brand are produced with high power and at the same time have an affordable price

The device has the ability to reverse rotation. The Zubr corded screwdriver is capable of adjusting the rotation speed, which occurs thanks to an electronic control system. The cross section of the cartridge in this case is standard and is 10 mm. The quick-release tool increases ease of use when changing tips frequently.

Purchasing such a model allows you to ensure high operational safety, since it has a system that blocks the “Start” key. It is also worth highlighting that the device is lightweight, and its warranty period is 5 years.

Planetary reductor

The drive sun gear is also pressed onto the rotor shaft. A bracket in the form of a rocker arm is mounted on the engine body, with the help of which the gear stages are switched.

Screwdriver gearbox

The differential gearbox can be enclosed in a plastic housing. The arrangement of gears in a planetary gearbox depends on the number of switched speeds and may differ in different models. In a two-speed power tool, the gearbox has three stages. The first stage contains:

• sun gear;
• fixed ring gear;
• planet gears, small gears that rotate inside the ring gear.
• toothed drive.

The second stage serves to transition from the first stage to the third when changing gears. It consists of a planetary gear, which, with the help of a bracket, moves to the first and second rows of gears, due to which the rotation speed of the cartridge changes. It also has built-in satellites and carrier. The third stage is connected to a crown gear with protrusions at the end, 5 satellites, and a carrier with a cross-shaped grip.

The tightening torque clutch (the force applied by the screwdriver when performing work), also known as the torque regulator, consists of cylinders and balls, a housing, a washer, and a spring.

The clutch blocks the operation of the screwdriver if the load on the rotation mechanism increases, and thereby protects the screws on one side from failure, and the engine and planetary mechanism from unnecessary overloads and premature failure.

If you switch the screwdriver to drilling mode, the spring tightens and presses the washer as much as possible so that the third stage ring gear is blocked and its rotation is prevented. Thanks to this, the operation of the cartridge is not blocked. This video shows how a screwdriver works.

Rotation adjustment clutch

It ensures that movement stops when work is completed, for example, at the moment of complete screwing.

This mechanism makes it possible to prevent the screw thread from breaking and the engine from overheating due to overload. Consists of a stopper, a washer and a spring, a threaded (adjusting) bushing.

The adjustment clutch is combined into a single mechanism with a cartridge. At maximum tension, the spring transfers the load to the fingers of the threaded bushing, which stops the cartridge case. After this, the rotational force stops. Depending on the design features of the screwdriver clutch, there are 5-25 adjustment steps.

Features of corded and cordless screwdrivers

In corded screwdrivers, the power source is a 220V electrical network and a power cord is built into the handle of the power tool. To work with corded power tools, an electrical outlet is required; this is a disadvantage of such tools. However, a constant power source and voltage of 220 V do not limit the power of such power tools. It's no secret that batteries are limited in this regard. They are also limited by operating time, after which the battery must be charged.

A cordless screwdriver with a rechargeable battery is appreciated by motorists who have to carry out repairs in the absence of a constant power supply, somewhere on the highway, and by builders, since remote construction sites are not always provided with electricity in a timely and stable manner.

Power supply and its characteristics

The screwdriver motor can be powered by mains or battery power. Models equipped with a wire for connecting to an alternating current network have limitations in operation and are less compact. However, they have increased power and operational reliability.

Screwdrivers with a constant current source are equipped with 1 or more batteries. Its power can vary from 9 to 36 watts. For solving household problems, the optimal power range is considered to be 12-15 W. The following types of batteries are used:

• lithium-ion (Li-Ion);
• nickel-cadmium (Ni-Cd);
• nickel metal hydride (Ni-MH).

They differ in voltage and service life. It is recommended to purchase screwdrivers with a 3.6 V Li-Ion battery. They are reliable and durable in operation. In addition, you should take into account the capacity of the power source, which directly affects the service life. It varies from 1.2 to 3.5 Ah.

Reference! It is advisable to purchase a model equipped with 2 or more batteries, which avoids interruption in operation. The technical documentation always indicates the charging duration; the shorter it is, the more convenient the tool.

When choosing a screwdriver, consider the purpose of the job. Professional tools are distinguished by increased engine power and 2-3 phases of gearbox operation. The case should be comfortable for the hand and comfortable for prolonged use. It is recommended that the spindle speed be adjusted, the minimum range is 0-1250 rpm. It is imperative to have a reliable and capacious power source; for convenience, it is advisable to purchase models with 2 or more lithium-ion batteries.

Top 3 best models

The construction tools market offers a wide range of similar products. We have selected the 3 most successful models:

DeWALT DCF887N-XJ. Compact brushless screwdriver from a famous American brand. It is painted in the manufacturer's traditional yellow-black color, which is convenient for searching in a cluttered object. Equipped with an internal hexagon chuck. There is a pulse mode and the possibility of shock operation. The brushless electric motor operates from an 18 V battery, the maximum speed is 3250 rpm. The minimum configuration does not include a case or an additional battery;

Makita DTP141Z. Professional instrument with impact and pulse modes of operation. Maximum torque – 150 Nm. Suitable for working with wood, metal, and effectively unscrews rusted nuts. Equipped with a brushless electric motor and an 18 V battery. Battery and charger are not included. Chuck with hex mount. It is possible to turn on the backlight, the handle is rubberized and fits comfortably in the hand. Supplied in a box, tool weight – 1 kg.

When purchasing a tool for household or professional tasks, you should pay attention to the cartridge. The choice of nozzles according to the type of shank depends on this

As a rule, high-power impulse models are equipped with a hex chuck only.

Changing attachments

Changing the attachment on a screwdriver is not difficult. The tool can be equipped with a quick-release chuck or a key-type chuck. Replace the equipment in both cases in a similar way. To remove a drill from a screwdriver with a keyless chuck and insert a new one or another type of equipment, proceed as follows:

• first, select a bit according to the size of the head and the type of slot on it (cross, straight or other) or a drill of the required diameter corresponding to the material in which the hole is to be created;
• spin the cartridge counterclockwise;
• in the center, between the spread cams, install the selected type of equipment;
• Rotating the cartridge case in the direction of the clock hand, clamp the nozzle.

You can remove the drill bit from the screwdriver (or another attachment) by holding the moving part of the chuck with one hand and pressing the start button with the other. Just first switch the direction of rotation to unwinding.

When a drill-driver is equipped with a key chuck, then to change the equipment do this:

• inserting the key into the recess for it, unscrew the cartridge;
• I install the nozzle;
• clamp it by turning the key clockwise.

There are models in which you can remove one type of cartridge, for example, a quick-detachable one, and replace it with a turnkey analogue . When choosing any option, you need to focus not only on ease of use, but you should also consider the pros and cons of each of them. Thus, the key chuck securely clamps the equipment, which is important when drilling, and the quick-release chuck allows you to quickly replace it, even with one hand (the other holds the handle, pressing the start button as necessary).

Purpose

Along with a jigsaw with saw blades, a screwdriver has become widespread due to its versatility, as it is designed to perform a wide range of installation work:

• Connecting workpieces with various types of screw fasteners: self-tapping screws, screws, screws, bolts, etc.;
• Drilling holes;
• Other operations that involve the rotation of some tool or special attachment (threading with a tap, mixing solutions and mixtures, etc.)

The screwdriver is compact, convenient and easy to use, and most importantly, it significantly facilitates and speeds up various technological operations. Driving 100 screws with a hand screwdriver takes a long time and requires a lot of physical strength. With a screwdriver this can be done just quickly. In addition, the need for any craftsman to tighten screws and drill holes arises very often, and here, well, you simply cannot do without a screwdriver.

What characteristics and parameters should you still pay attention to when choosing a screwdriver?

The material above describes various characteristics and features of screwdrivers, however, you need to pay attention to the fact that some others have been tested

Brand (manufacturer)

The eternal dilemma of manufacturers is to produce a product that is more expensive and of better quality, or cheaper, but reduces the cost due to quality. Each manufacturer decides this issue himself, so the buyer’s trust in the manufacturer determines the expected level of tool quality. Let's look at the following statistics.

Additional accessories and equipment

• Screwdrivers, like any other tool, can be supplied either in a cardboard box or in a suitcase (case). The advantage of the case is obvious, although in the end the price of such a screwdriver is also higher.
• Now it has become the norm, but, nevertheless, you need to pay attention to the inclusion of two batteries in the kit, and not one.
• Bits and drills included.
• Additional elements (for example, a flashlight).
• Spare parts (eg replacement brushes).

Spindle lock

Above, we touched on the force limiting device, when triggered, the spindle is disconnected from the chuck and rotation stops. Some operations, such as drilling, do not require force limitation. For such cases, a screwdriver spindle lock is required.

Engine brake

When the power button is completely released, the screwdriver chuck should stop immediately. This is ensured by the "Engine brake" function.

Backlight

Illumination of the work area is sometimes very convenient, since sometimes you have to work in the dark or in limited spaces where there is not enough lighting.

Service centers

Find out if there are official sales representatives or service centers in your city to resolve warranty issues or purchase additional accessories.