Inside the Electric Screwdriver

Electric screwdrivers are fascinating because they integrate batteries, motors, gears, and a switch into a compact and powerful unit. Let’s take one apart and explore its components! Here’s the screwdriver we will examine:

Power & Work Tools Image Gallery

When you remove the cover, you’ll find the essential parts of the screwdriver neatly arranged from one end to the other. These include:

Ridges inside the casing and two long pins work together to hold all these components in place.

The internal components are quite straightforward. In the next section, we’ll examine the switch and how it powers the motor.

Switch Block

The switch block actually serves two main functions in this screwdriver:

A view from both the inside and outside of the screwdriver’s switch

The two metal loops at the bottom of the switch are placed on either side of a contact that connects to the motor. In the neutral position, the contact remains unconnected. However, when the switch is moved, one loop touches the contact, completing the circuit.

The wires transport electricity from the batteries. The batteries and the recharging contact are located inside the screwdriver’s handle.

Gears transfer the motor's movement to the screwdriver bit. In the next section, we’ll explore how the gears interconnect.

Electric Motor

The electric motor used here is a typical DC motor. To learn more about the components of a real electric motor, check out How Electric Motors Work.

At the end of the motor is a small gear with six teeth. This gear fits into the center of the planetary gear system, as illustrated here:

A gear connected to the motor is placed at the center of the three smaller gears.

This gear system is the core of every electric screwdriver. A basic electric motor alone doesn’t have much power. You can easily stop the rotation of a small motor just by grabbing its axle. But when the motor’s speed is greatly reduced by gears, it gains the force necessary to drive a screw into wood with ease. In this screwdriver, the dual planetary gear system has a 56:1 reduction ratio. This means the motor must turn 56 times for the chuck to make a single rotation. As a result, the chuck turns much more slowly compared to the motor, but it generates significantly more torque (it takes 56 times more force to stop the motor from turning due to the gear ratio).

Here’s how the 7.5 turns are calculated. The center gear must rotate roughly three times to turn its three surrounding gears once. These gears then need to rotate about two and a half times to complete a full revolution around the outer ring, totaling around 7.5 rotations. The outer ring remains stationary, with the other gears simply moving around within it.

The gear system consists of two identical layers, one on top and one on the bottom (the bottom layer is hidden in the images, behind the top one). The top layer attaches to a small table, which has a second 6-tooth gear beneath it. Due to the movement of the top layer, this gear turns once for every 7.5 rotations of the motor. The bottom 6-tooth gear takes 7.5 turns to move the bottom gears around the ring, resulting in a gear ratio of approximately 56.25:1. The bottom gears are connected to a piece of metal that rotates the chuck once for every 56 motor rotations.