Introduction: Safe Box With Combination Lock From Cardboard
This tutorial show you how to made a Safe Box with Combination Lock from Cardboard. Follow the following steps in this instructable if you want to repeat and watch video to enjoy :)
Materials and Tools :
- 2 x Cardboard 50x80cm
- 1 meter x Tube PVC diameter 12mm
- 2 x Pop-sticks
- Hot Glue sticks
- Metric ruler
- Pencil compass
- Pencil
- Cutter Knife
- Hot Glue Gun
- Brush
Step 1: Making Gears Wheel
First, cut the cardboard according to the following forms:
- 3 circles of diameter 80mm,
- 1 circle of diameter 60mm,
- 1 rectangle 12x260mm
Then they are glued perfectly superimposed following the same axis.
To mount the gear teeth, I remove an upper layer of the rectangle and glue the other part to the perimeter of the gear body.
We need a total of two gears wheel : the first to convert the rotational movement into a translational movement. the second is used to reverse the direction of rotation
Step 2: Shaping the Safe Door
Using a cutter, we start by cutting the outer frame size 34x42cm and then cut the cardboard to form the door size 25x31cm.
Step 3: Making the Holes
To make all the holes needed in this project, you can simply use a pencil. Holes are required to enter the axes of rotation of the gear wheel and the other lock wheels.
We need a total of 3 holes in this project
Step 4: Fixing the Gear Wheel
Using a cutter, we start by cutting two 20mm pieces of pvc round tube. The pvc tube is 6mm in diameter, it is the axis of rotation of the two gears wheel. The first gear is glued to the upper gear and the second is glued to the safe door. The glue to use is hot glue.
You have to pay attention to the alignment of the two gears.
Step 5: Building Tongues Lock
Using a cutter, cut the pvc tubes of 12mm diameter into pieces of the following length: 2x28cm, 18cm and 35mm.
I glued it by following the picture attached.
To build a rack mechanism, cut 2 rectangles of cardboard 12x6mm, remove the upper layer to find the teeth. They are glued on end of the internal faces of the two tubes. Please see the picture below.
Step 6: Shaping Locking Wheel
I start by cutting the cardboard in 4 circles of diameter 30 mm. then, we will cut each of the 3 circles into 3 pieces: two half circles and a central rectangular piece of width 14mm. the semicircle pieces are glued superimposed as shown in the attached picture.
Step 7: Mounting
This step is used to mount the parts already built. We start by making two holes for rotation axes of the two locking wheels, always we can use a pencil for the perforation. After the installation of the two locking wheels, the tongues lock is placed in its position as shown in the attached picture. we can if we want to build a box that covers all the locking mechanism.
Step 8: Front of the Box Door
For each end of the three axes, we glue a circle with a diameter of 25mm. Then we glue two numbered wheels from 10 to 85 for example 35mm diameter using hot glue.
Finally, we glue the opening lever on the third axis. Regarding the lever, you can choose any shape that you like.
Step 9: Door Rotation Solution
For the fixing and building the system of rotation of the door, I use two pieces of wooden sticks and I enter them in the groove of the cardboard at a distance of 2 cm from the edge as figure in the picture attached.
Step 10: Building the Box
Finally, we cut the cardboard into 5 rectangles whose dimensions are as follows :
- 2 rectangle 30x34cm
- 2 rectangle 42x30cm
- 1 rectangle 42x34cm
After, we glue them using hot glue, always keeping the perpendicular angle between them.
Step 11: Watch
In order to not miss any details and to follow all the real chain of the instructable, enjoy to watch the video tutorial attached.
Hoping that you liked this creation !

First Prize in the
Cardboard Challenge
58 Comments
Question 1 year ago on Step 8
how many pieces are there total for this project?
Question 1 year ago
Why is the video private? My student is trying to make this and the instructions are not detailed enough for him to follow. Please can you share the video?
2 years ago
THAT IS THE BEST EVER IT SHOULD BE GRAND PRIZE NO MATTER WHAT IM MAKING IT!!!!!!!!!!!!
2 years ago on Step 11
I would love to watch the accompanied video to make sure I'm doing it right. I'm making this with my 6 year old son as this is thee best one I've seen on the internet. Is there a way to make the video not private?
Question 2 years ago
can you upload the Youtube video?
3 years ago
It looks awsome!Keep it up!
3 years ago
Fantastic! I love this.
Tip 3 years ago
you should use wood instad of cardboard but it is a DIY so i guess it was good
3 years ago
should have won grand
his use of different aspects of cardboard is brilliant and very creative, great job
3 years ago
Incredible work! Very ingenious!
3 years ago on Step 11
Awesome. Nuff said.
3 years ago
Very cool project!
3 years ago
This is super cool! I love that you used the corregation of the cardboard to make gears!
Since the holes/cutouts on the back of number dials go all the way across, does it technically have 4 combinations that can open it? Like 40 and 75, but also the numbers on the exact opposite side of the dials?
Reply 3 years ago
This Problem is already remedied in steps 6 and 7. I already edited the shape of Locking wheel. Currently, the only combination allowed is 40 + 75.
Reply 3 years ago
Ah, nicely done :)
4 years ago
it looks cool i have to try it i am doing it for a school prodject
4 years ago
Good Job ! Voted :)
4 years ago
This deserves the Grand Prize in the Cardboard Challenge. So awesome. Voted!
Reply 4 years ago
it s good execution but it's not his idea.. it's been on Youtube for years, he just copied the design..
Reply 4 years ago
KC, it's doesn't matter if it's an original idea or not. If original ideas mattered, then why is there an instructable on this site for changing spark plugs? Has no one ever changed spark plugs before?
This site is about posting instructions on how to do or make something. To win a contest is as much about how cool your project is, how well it's made and how well your instructions are. Essomar wins on all 3 counts and more in my book. (And the Safe Box is new to me. I'd never seen one b4. Good work Esso and GL!)