Introduction: How to Build a Cardboard Combination Padlock

Picture of How to Build a Cardboard Combination Padlock

Today I will be showing you how to make a combination lock- out of cardboard! This is a fun build and a perfect way to get rid of empty boxes sitting around. Have any questions? Pop a comment below and I'll help. I am entering this in the toy contest so if you like my work, please vote!

Step 1: Tools and Materials

Picture of Tools and Materials

Not many things are required to make this lock.  It's mainly cardboard.

-Box cutter / razor blade
-A cutting mat (so you don't gouge your table)
-Hot glue gun and extra glue sticks
-A compass (the kind used to draw circles)
-Hole punch (apparently this can be used to punch the holes for the washers and such. (thanks to swhitaker2 for discovering this))

-Corrugated cardboard
-Two new pencils
-Large paperclip

Step 2: Making the Rotors

Picture of Making the Rotors

The rotors are the wheels inside of the lock that determine what the combination is. All three must be lined up perfectly so that the lock can, well, unlock.

1) Cut out three circles that are each four inches across.
2) Poke a hole in the center of each circle with the pointy end of the compass, the do the same with the pencil.
3) Draw and cut out a notch in each rotor about 1/2 in. wide at the top. Make sure you don't cut all the way to the center, but at least one inch deep.
4) Cut out two tabs that are 3/4 by 3/4 in. Then cut one tab that is 1 and 3/4 inches by 3/4 in. Scraps of cardboard are good for these kind of parts.
5) Make a cut-out in one of the rotors, about 3/4 inch deep and 1/8 inch wide, or however thick your cardboard is.
6) Attach the tabs to the rotors using hot glue as shown in the picture. Don't copy my layout exactly otherwise the combinations will be identical. Also be sure to arrange the notches so that they're all facing the same direction when you attack the tabs.

Step 3: Making the Dial

Picture of Making the Dial

Now let's make the dial. You know, the part that you spin with all the numbers on it!

1) Draw three circles 1.5 inches in diameter and one circle 3 inches in diameter.
2) Cut them out.
3) Poke holes in the centers with the compass.
4) Line them all up on a pencil. Glue them together but don't glue the pencil. You can trim the small wheels if there is any excess cardboard around them.

Step 4: Cutting the Washers and Supports

Picture of Cutting the Washers and Supports

There's not much to this step.

1) Cut out four washers, 1/4 inch by 1/4 inch each. Again, scrap is good for this.
2) Make two strips that are 3 and 3/4 inches long byabout 1 and 3/4 inches wide.
3) Poke holes in the short supports that are 1/4 inch down from the top and are centered in the support.
4) Make one strip that is 4 and 1/2 inches long by about 1 and 3/4 inches wide.
5) Poke a hole in the long support that is 1/2 inch from the top and centered in the support.

Step 5: Build the Independent Rotors

Picture of Build the Independent Rotors

I call these the independent rotors because they can (and have to) spin freely.

1) Cut the eraser end of the pencil into a 1 and 1/4 inch piece. Save this piece for later. Cut a four inch piece off the remaining bit of pencil. We'll use that now.
2) Gather the materials needed:
   -Two rotors. One with the long tab and one without.
   -The two short supports.
   -Three washers.
   -The four inch pencil you just cut.
3) Slide on washer on the pencil and hot glue it to end.
4) Slide the rotor with the long tab onto the pencil but DON'T GLUE IT!
5) Slide another washer on the pencil and against the rotor. Make sure the rotor can move, but that it will stay in whatever position you put it in. Glue the washer in place.
6) Slide and position the last washer about an inch away from the rotor. Don't glue it in yet.
7) Slide and adjust the final rotor so that when turned, the tabs make contact, but don't slide it so close that the rotors can't move at all. Oh, and make sure the tab points towards the first rotor.
8) Glue the third washer in place.
9) Glue one short support next to the second rotor, following the same guidelines as in step 5 above.
10) Glue the other support about two inches away, at the end of the pencil.

Step 6: Making the Locking Bar

Picture of Making the Locking Bar

This is the part that checks if the correct combination was dialed in.

1) Cut out two pieces that are 1 by 1 and 1/2 inches long. Poke holes in them 1/4 inch from the bottom and 1/2 inch from the side.
2) Bend the large paperclip so that there is a four inch long side and two perpendicular ends, like a giant staple.
3) Choose what shape you want for your indicator. This is what you turn to unlock the lock, so make sure it can handle the abuse. The arrow I chose wasn't strong around the axle hole, so it didn't work that well.
4) Test fit the parts together as shown in the picture. Don't glue anything yet except the indicator.

Step 7: Building the Base

Picture of Building the Base

Time for the base! Too bad all of them belong to me. (Not so obscure reference)

1) Cut out  a flat piece of cardboard that is 8 inches by 11 and 1/2 inches.
2) Using the box cutter, very gently cut the top layer of the cardboard at a line that is 5 and 1/2 inches from one side, and 6 inches from the other.
3) Make holes at the following locations on the 6 in. by 8 in. side, with the 8 inch sides on top and bottom:
   -3 inches across, 3 and 1/2 inches up.
   -5 and 3/4 inches across, four inches up.
4) Cut out little triangles from the already existing corners of a box (just to make sure they're square) and glue them into place at the edges of the base. Also, glue along the outside and inside of the fold.

Step 8: Final Assembly

Picture of Final Assembly

Congratulations! You made it! Oh, wait, nevermind. One more step. Good luck!

1) Assemble the dial and rotor by gluing the dial to the pencil stub (you still have that, right?) and inserting it through the lower hole in the base. Slide a washer on and then glue that and the rotor to the pencil, making sure that the dial can rotate.
2) Glue the independent rotors to the base so that the pencils line up and the rotors' tabs are the right spacing apart, like on the other pair of tabs.
3) Take the indicator pencil and slide it into the upper hole on the base so that the pencil sticks out about 1/2 inch from the front.
4) Slide the locking bar and support onto the pencil like before and glue the paperclip to it's holders. Glue the support down and make sure it's further back than the rotors.
5) Cut out a small piece about 1 inch by 1/2 inch.
6) Move the indicator to wherever you want the "lock" position to be. I find that 45 degrees right of vertical works well. Mark that position.
7) Move the locking bar to about the position shown in the ninth picture while holding the indicator in the "locked" position. Mark the edge of the paperclip holder.
8) Glue the small piece you just cut to the mark you just made. This prevents the locking bar from turning too far up. The locking bar support itself stops the bar from turning too far down.
9) Once the locking bar is correctly positioned, glue the paperclip holders to the pencil. Make sure that the holder closest to the indicator is flush against the side.
10) Turn the rotors so that all of the notches are facing the locking bar. Turn the locking bar into the notches. when the bar stops, mark the position of the indicator on the front. This is the "unlocked" mark.
11) Make a number indicator. This can be an arrow or other symbol that indicates the current number.
12) Turn the dial three times clockwise. All of the rotors should be turning after the third turn, if not sooner. turn the dial so that the notch on the rotor farthest back is positioned directly in front of the locking bar as it descends. Make a mark on the dial where you put the number indicator.
13) Turn the dial once to the left. Then keep turning it so that the middle rotor's notch is lined up with the locking bar as well. Make a mark on the dial where you put the number marker.
14) Turn the dial right until the notch on the closest rotor is also lined up with the locking bar. Make a mark on the dial where you put the number indicator.
15) Using these marks, evenly space out numbers on the dial. I usually use 10 to 12 numbers.
16) Add the "locked" and "unlocked" labels to the marks near the indicator you made earlier.

Step 9: Whew! Finished!

Picture of Whew! Finished!

Wow. Finally.

You deserve a hand. Really, you do. You have built your own cardboard combination lock!

Need help? Ask in the comments!
Remember to post pictures of your lock if you make one. I'll add them to this page.
I do believe that this is the first lock like this ever, because I haven't seen any others on the internet, but I may be wrong. Let me know!

Thanks for your time! Hope you enjoyed!


LalaDGDG (author)2017-08-02

I am trying to make one using paper and straws. Nice instructable!

ZachH2 made it! (author)2014-09-24

Hey there, I've now made 3 of these with kids! It's pretty awesome. To make it easier for kids to cut and follow along, I created the outlines of a majority of the pieces in Illustrator. I've attached the PDFs I've made here. Thank you!

waterrocketsrule (author)ZachH22017-04-21

Weres the PDF?

ZachH2 (author)ZachH22014-09-24

Oops, those pictures weren't exported correctly! Here's the proper ones...

tardis fan (author)ZachH22014-09-24

Wow, so cool! That's a great help! I'm happy to hear that the kids are enjoying it!

Acedestruction (author)2016-05-17

It won't work for me. the rotors turn when I turn the dial and won't stay in the same place.

makemechanisms02 (author)2015-09-20

I'm a 12 year old girl who made this! rly good intructions and easy to follow. thank you!

Technovation (author)2015-04-15

can u put a video of it working please

aryan dewan (author)2015-03-09

are the washers 1.25by1.25 inches in step 4

aryan dewan (author)2015-03-09

are the washers 1.25by1.25 inches in step 4

aryan dewan (author)2015-03-09

are the washers 1.25by1.25 inches in step 4

aryan dewan (author)2015-03-09

or reply me

aryan dewan (author)2015-03-09

please make a video

aryan dewan (author)2015-03-09

how to lock a box with it

skulljo (author)2015-02-08

I dont like a thing of instrucable that it take very much time ti load the pictuers.

skulljo (author)2015-02-08

I dont like a thing of instrucable that it take very much time ti load the pictuers.

skulljo (author)2015-02-08

I dont like a thing of instrucable that it take very much time ti load the pictuers

skulljo (author)2015-02-08

I dont like a thing of instrucable that it take very much time ti load the pictuers

skulljo (author)2015-02-08

I dont like a thing of instrucable that it take very much time ti load the pictuers

keithaporter (author)2015-01-13

I think the washers of step 4 are 1.25 inches by 1.25 inches, not 0.25 inches by 0.25 inches.

Velin9 (author)2013-07-23

LOL Easy to unlock! Just light it on fire! XD. LOL HAHAHAHA

ThePorsche8 (author)2012-06-06

u did a really nice job! i really want to build it but it looks so complicated. can you give some tips on how i can build it without being worried please.

that will give me a lot of help.

tardis fan (author)ThePorsche82012-06-07

Thanks a lot!

To begin, lay out all tools and materials in an organized fashion on your work surface. Once you're ready to start, take each step one at a time, and don't rush. You can always start over if something goes wrong. Remember to clean up the little scraps that aren't needed off your work surface, because having a clean desk helps a ton.

And believe me: it really isn't nearly as complicated as it looks once you start!

Hope I helped, and good luck!

insttuctable8 (author)2012-04-25

cool project you should make another that can actually lock a box, And make it smaller because it is huge please try

macrumpton (author)2012-04-02

This looks awesome.
I think it might be even better if you used laminated layers of solid cardboard, like the stuff used for cereal boxes rather than the corrugated stuff, as it would be a lot more durable. After all it is a lot of work, so you want it to last.

244 Jake (author)2012-03-10

Great post as to how the lock system works, Any way a completed safe could be shown.

Yesterday I received this. Most cool. I do NOT beleive it's evil to show a different way to do the same thing. Even if this was 3 months after YOURs.

Could you do the next step, Please, show how to connect to a door handle. I want to make a big Toy Gun Safe, out of card board, say the card board box a refrigartor would come in..

Big Jake

samaw129 (author)2012-01-24

hey, im back,
any way to add a door? trying to win a bet that i built a cardboard safe

tardis fan (author)samaw1292012-01-25

You could try to connect the locking bar to a linkage so it draws back a bolt unlocking the door. Experiment!

samaw129 (author)2012-01-22

hole punchers work well for the washers :)

tardis fan (author)samaw1292012-01-22

Never actually thought about using hole punchers for that. I might add it to the instructable.

samaw129 (author)tardis fan2012-01-23

haha yeah worked for me!

thing 2 (author)2012-01-17

Could you upload a video that shows how it works/a demonstration?

tardis fan (author)thing 22012-01-22

Most likely I will. Just have to find the time. . .

BuhBomb (author)2012-01-15

This reminds me of Furio Tigre's cardboard badge...

LiftAndLove (author)2012-01-07

you should make the lock mechanism smaller, so you can put stuff in the box.that's what im going to do.

tardis fan (author)LiftAndLove2012-01-08

Cool! Post some pics when you do.

ghostpotato (author)2012-01-05


i made this and only tool me about a hour and it works awesome.

might make a full case for it so you cant just look over the back and align them.
if i make that i might post some pictures. O and also knex rods are a good substitute if you don't want to use up pencils

p.s. be careful when hot gluing i got a nasty burn in my left pointer so now it hurts to type. lol why am i making this comment so long then??

this is truly ingenious and im giving a 5* for sure

my finger hurts :(

LiftAndLove (author)ghostpotato2012-01-07

i was hot gluing once, and I was kicked in the head. it burned me);

ghostpotato (author)ghostpotato2012-01-05

oops in second line i made a mistake i meant only took me an hour not tool me an hour srry

tardis fan (author)ghostpotato2012-01-06

I'd be interested to see how the covered lock turns out.

Hot glue burns are nasty, aren't they? I got one while making the base and had to take the picture as fast as possible!

heathbar64 (author)2012-01-01

Very funny thing. I made one very similar to this a few month ago. My daughter had her first combination locker at school and I thought knowing how it worked would help her with getting it open.. too bad I didn't take a picture.

tardis fan (author)heathbar642012-01-05

This model is good at teaching about locks. My family has learned from it as well.

rimar2000 (author)2012-01-01

WOW, what a good work!

tardis fan (author)rimar20002012-01-05

Thank you!

tinker234 (author)2012-01-04

wow great work

tardis fan (author)tinker2342012-01-05


Onyx Ibex (author)2012-01-01

I was just wondering why no one has posted an ible on this. It is very amusingly handy for all sorts of rediculousness. Well done!

tardis fan (author)Onyx Ibex2012-01-01

Thanks for the complement! Try your hand at making one!

kelseymh (author)2011-12-31

Now that is really awesome. Way back when I was teaching physical and information security courses, this would have been a brilliant take-home project for my students.

tardis fan (author)kelseymh2012-01-01

Thanks! If you make one, be sure to let me know!

About This Instructable




Bio: I love to invent and build things, and am a huge fan of Doctor Who!
Add instructable to: