Why the Combination Lock?
AUG 2026
This was the first product I decided to teardown and analyze for this project. And even though I've used this Bic pencil for years, I never considered how it actually works.
There are countless mechanical pencil designs from history, and surely some fancier mechanical pencils you could use, but this Bic pencil is still being mass produced and selling in the exact same form almost 40 years later.
The main question we want to answer: Why does the lead continue to press out, when the eraser is pressed and released? Let's take a closer look.
How Do You Open the Lock?
Text here
Let's See What's Iniside!
Let's take the assembly apart to see what's going on.
Let's Look at the Cam Assembly First
Let's take the assembly apart to see what's going on.
Let's Look at the Cam Assembly First
Let's take the assembly apart to see what's going on.
Each Cam has a notch
In order to remove the shackle and unlock the lock, we need all three grooves lined up. Let's cut away the housing and look inside.
Let's walk through how each Cam moves and how we can solve this puzzle. Anytime we rotate the dial, Cam A moves. They're connected.
What if we keep spinning the dial?
Let's Clear the Lock First
Before you enter your combination, you need to turn the lock 3 times to reset it.
There are three Cams. Each Cam, individually, is quite simple. They each have a notch and 1 to 2 'bumps'. The first Cam is attached to the dial. They always move together.
Let's Unlock It!
Before you enter your combination, you need to turn the lock 3 times to reset it.
Why do you have to turn past the 1st number?
Before you enter your combination, you need to turn the lock 3 times to reset it.
