What's inside an electric screwdriver? See for yourself
Temitayo Oketola | April 06, 2022Electric screwdrivers are portable electric devices used for driving (and removing) screws effortlessly. Like the conventional manually operated screwdriver, an electric screwdriver features a handle and shaft with a flat (or cross-shaped) end that fits into the top of a screw.
However, because electric screwdrivers fetch energy from an electric source, they are faster, more efficient, and more versatile than conventional screwdrivers. For instance, electric screwdrivers offer a broad range of rotational speed and torque, making them ideal for several industrial applications.
The electric motor and gear system are two essential components that play a crucial role in this screwdriver’s impressive performance.
The electric motor
Electric motors convert electrical energy into mechanical energy (in the form of shaft rotation). A direct current (DC) motor is commonly used in electric screwdrivers. It works based on the principle that whenever a current-carrying conductor is placed in a magnetic field, it experiences a magnetic force.
DC motors feature two key components: a stator (or stationary part of the motor) and a rotor (or the rotating part of the motor). The stator typically contains permanent magnets, while the rotor comprises coil windings. A magnetic field is created within the stator when a DC source powers the motor. This magnetic field attracts and repels the magnet, causing the rotor to rotate and generate torque (or turning force).
The torque generated by the motor is mathematically related to the motor’s angular speed and output shaft power, according to the equation:
Where:
P = motor’s output shaft power
N = speed of motor in revolutions per minute
However, the torque generated by these motors is usually small, especially at high rotational speeds. The gear reduction system is one essential mechanical component that solves this torque challenge and makes electric screwdrivers sought after in several industrial assembly applications.
Gear reduction system
The gear system is the heart of the electric screwdriver: it allows the device to have enough strength (and torque) to drive screws effortlessly. An electric screwdriver’s gear system is essentially a planetary gear, consisting of a centrally pivoted sun gear, a ring gear and three planet gears that rotate around these (See Figure 1).
Figure 1: Planetary gear found in electric screwdrivers. Source: [beysim/Adobe Stock]
The sun gear acts as the input gear from the motor and drives the planetary gear, which then drives the chuck; the part of the screwdriver that holds the drill bits to tighten or loosen screws.
An electric screwdriver’s gear system can achieve a gear reduction ratio of 56:1. In such a scenario, the screwdriver’s chuck will rotate once for every 56 complete rotations of the electric motor’s shaft. Although this would mean that the chuck moves very slowly relative to the motor, it makes it possible for screwdrivers to transfer high torque while utilizing a compact design.
Most electric screwdrivers rely on some sort of motor-gear assembly to function. However, there are slight variations in the designs of these tools. For example, cord and cordless electric screwdrivers are two different screwdrivers that engineers can choose for their projects.
Cord vs. cordless electric screwdrivers
Cord electric screwdrivers require that the device be plugged into an electric outlet before it can be operated. In contrast, cordless (or portable) electric screwdrivers are battery-powered screwdrivers that can be used even in applications without an electric outlet.
Cordless electric screwdrivers come in different voltage ratings ranging from 3 V to 11 V, with a higher voltage rating translating to higher tightening torque. Portable electric screwdrivers with a voltage rating of less than 4 V are ideal for light-duty applications like driving small screws into plastic and softwood materials. In contrast, a higher voltage electric screwdriver is ideal for heavy-duty jobs like assembling hardwood and ceramic parts.
Straight vs. pistol electric screwdrivers
Straight electric screwdrivers have their body in the screwing axis, while pistol screwdrivers have an angled body. The straight screwdrivers are ideal in applications where there are challenges accessing small assembly areas, such as hanging systems. In contrast, pistol grip screwdrivers offer more stability and grip; they are ideal in applications where there are no stringent thrust requirements along the tightening axis
Summary
Electric screwdrivers can meet several applications' torque and tightening requirements so long as they are selected correctly. Therefore, engineers and operators are advised to reach out to electric screwdriver suppliers to discuss their application needs.