MECHANICAL PENCIL

BREAKDOWNS

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An illustrated celebration of the engineering around us

MECHANICAL PENCIL

An illustrated celebration of the engineering around us

MECHANICAL PENCIL

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Why the Combination Lock?

AUG 2026

Until taking this lock apart, I hadn't used a combination lock in years. Maybe since high school? But I'll never forget the series of steps to unlock it. I remember always turning it countless times just to be sure I had reset it. And sometimes forgetting to turn past the first number during the unlocking. And thanks to this teardown, now I know why both of those steps are necessary, not just recommendations!

How Do You Open the Lock?

Just to be sure we're all on the same page before we get into this!

Here's your combination. Don't forget it!

1) Turn the dial 3 times Clockwise and stop on the first number, 18

2) Turn the dial Counterclockwise, past the first number, stopping at the second number, 39

3) Turn the dial Clockwise to the third number, 23 and open the lock

1) Turn the dial 3 times Clockwise and stop on the first number, 18

2) Turn the dial Counterclockwise, past the first number, stopping at the second number, 39

3) Turn the dial Clockwise to the third number, 23 and open the lock

Let's See What's Iniside!

Let's take the assembly apart to see what's going on.

OPEN UP

Cam Assembly

Back Cover

Back Plate

Inner Housing

Housing

Shackle Assembly

Cam Assembly

Back Plate

Back Cover

Inner Housing

Housing

Dial

Shackle Assembly

Let's Look at the Shackle Assembly First

Let's take the assembly apart to see what's going on.

OPEN UP

Let's explore the Shackle system

Let's look at how these parts move independently

LEVER

PLUNGER

SHACKLE

Click through to see how these parts move

Let's put the whole shackle system together now

Let's look at how these parts move independently

ALIGN

SCRAMBLED

Let's open up the lock!

Let's better understand the Cam assembly now

Let's take the assembly apart to see what's going on.

OPEN UP

OPEN UP

Cam A

Dial

Cam B

Cam C

Spacer x 2

Washer

Spring

Shaft

In order to remove the shackle and unlock the lock, we need all three notches lined up. Each Cam has pins that will help us align the notches. Let's understand how these interact with each other.

DIAL:A

A:B

B:C

Each Cam has a notch. All three notches must line up to unlock the lock.

DIAL:A

A:B

B:C

Each Cam has a notch. All three notches must line up to unlock the lock.

Let's Reset the Lock First

Before you enter your combination, you need to turn the lock 3 times to reset it.

CAM A

CAM B

CAM C

At first, turning the dial only moves

Cam A

Cam C

Cam B

Cam A

Time to Unlock the Lock!

Before you enter your combination, you need to turn the lock 3 times to reset it.

RESET

Pin B

contacts

activating

Cam C

Pin C

All Cams move together and the lock is reset!

Cam C

Cam B

Cam A

What happens if you don't turn past the 1st number?

Before you enter your combination, you need to turn the lock 3 times to reset it.

RESET

The lock is already reset. Let's begin.

Thanks for reading! Want More?

I'm in the process of illustrating some fun exploded views and cutaways. Head over to Instagram to take a look. And sign up if you want to know about any future product breakdowns or updates.

Thanks for reading! Want More?

I'm in the process of illustrating some fun exploded views and cutaways. Head over to Instagram to take a look. And sign up if you want to know about any future product breakdowns or updates.