S1E2: How do Electric beard trimmers work?
I used a beard trimmer for the first time during my undergrad at NIT-Trichy, India. Even though I didn’t have a beard as such, I had a mustache and decided to experiment with it. Since then, it has helped me go about my day. And I was fascinated by how this device functions when I was meddling with it.
Electric Trimmer was invented in the year 1921 by Leo Wahl. Several inventors have come up with different designs since then. But I chose to explore the working mechanism of the trimmer that I use. So let’s go!
Structure
Casing
A rigid outer casing holds the components of the trimmer. A removable piece is at one end of the trimmer. Thus you can clean the insides after removing them.
Blades
The removable part of the trimmer has two blades. One of them is stationary and the other one can slide back and forth. The stationary blade comes in contact with your skin. In contrast, the movable blade is at a clearance to trim the hair without bruising your skin.
Motor
A motor powers the blades to slide back and forth through a mechanism we’ll explore later. To the motor shaft, you can find a small protruding rod that’s at an offset from the center of the motor’s spinning axis as seen in the following gif. As the motor is spinning, the protruding rod goes in circles due to its offset.
V-shaped fixture
You can find a V-shaped fixture (on the removable part of the trimmer) that can move along with the moveable blade. When you attach the removable part of the trimmer to the casing, the motor’s protruding rod at the end always slides into this V-shaped fixture. This is due to the smaller offset of the rod from the center than the gap between the V-shape itself. By designing it this way, it is made sure that the motor and the V-shaped fixture will always be linked when the removable part of the trimmer is fixed. This linking is necessary to make the blades slide back and forth using the motor (mechanism discussed later).
Helical Spring
Recall that the moveable blade is rigidly attached to the V-shaped fixture, so they move together.
A helical spring is attached to the removable part as seen in the gif. The ends of the spring are then extended to connect with the V-shaped fixture, thereby applying force against the stationary blade.
Working Mechanism
Once the motor is turned on, it starts spinning with the protruding rod at the end of the shaft at an offset from the center. The V-shaped fixture is constrained to move linearly back and forth due to the way it’s attached to the helical spring. Recall that the moveable blade is attached to the V-shaped fixture, so they move together.
The protruding rod from the motor is in the same place as the pencil (from the previous gif) when it’s connected to the V-shaped fixture. Hence, as the protruding rod is spinning in circles, it pushes the V-shaped fixture back and forth linearly. With respect to the V-shaped fixture, the protruding rod moves along its width. This is similar to the Scotch Yoke mechanism’s gif that you see here.
Trimming mechanism
When the blades slide across each other, hair that’s between the teeth of the blades is thus trimmed. When you turn off the trimmer, the helical spring acts as a damper to bring the blades to a stop in a much shorter time. I don’t know if it was intended but it’s cool.
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