Introduction: Laser Cut Cryptex - Puzzle Box

This project has been made on a laser cutter that I used at FabLab Innovation (

Ever since seeing the movie - the Da Vinci Code - I have been fascinated with the cryptex, a small scale combination vault, that can only be unlocked by entering the right word on the scroll, allowing the user to pull out a tube which contains some sort of secret.

I decided to construct my own cryptex using laser cut parts, by that I mean only laser cut parts. In this project I developed 3 versions, an initial prototype to see if I could construct the basic mechanics in the cryptex, a second version that had a more aesthetically pleasing design, and the third and final version that had some improvements, that I came up with on my own. The cryptex has a total of 343 parts that are glued together. In this instructable I will describe the process and thoughts behind the different features in the cryptex and how I build it. I will also include the files for building one yourself.

For the steps about assembling the cryptex, I have added some exploded views made in CAD.

If you like this instructable, please consider voting for it in the Full Spectrum Laser contest by clicking vote in the upper right corner of this instructable, I would really appreciate it. Thank you in advance.

Step 1: The Final Version

Before going through the process of creating this cryptex. I will show the final version.

The final version has the ability to lock in secrets using 10 discs with 26 letters on each disc, that is a total of 26^10 different possibilities or 141167095653376 different possibilities, of course, in practice this is not true, because a cryptex will normally contain a keyword that makes sense, eg. in the Da Vinci Code the keyword is "apple", so a lot of possibilities can be ruled out, eg. words like "ehuakebnps" which is just a sequence of random letters, this can of course also be the keyword, but it is highly unlikely considering that a cryptex is normally unlocked through some kind of riddle.

In the first two versions, I had some issues with positioning the letters 100% correctly, so it could be difficult to unlock the cryptex, so in the final version I added a "click" function, where the disc would be turned 1/26 of a turn and click into position, it could also only be turned clockwise (when looking from the right hand side), this made it far easier to position the letters, and also gave a nice rattle sound similar to the one that can be found in a ratchet, while the mechanism I used in this cryptex, is almost identical to the mechanism found in a ratchet. I also raised the disc with the letters, making turning the disc a fair bit easier, since I expected some resistance from the clicking mechanism.

I can of course not claim the mechanical design in the cryptex as my own idea, since it is exactly how a standard combination bicycle lock works, but the idea of inserting a spring loaded gear to add the clicking effect, I believe is original. It might be that somebody else got the same idea, but I came to this idea independently.

The whole cryptex is made entirely out of 3 mm. MDF, and uses a total of 343 parts, though 260 of those parts where the individual letters, because each letter had to be inserted so the cryptex could be made to open up with a chosen keyword. Assembling one takes up to a few hours. The whole thing is assembled using only PVA glue, and afterwards I gave it some WD40 to make it turn smoothly, though in hindsight using grease would have been better since MDF has a tendency to suck up liquid and expand (though I have had no issues with that so far), and not everybody likes the smell of WD40, I do not mind it though.

Step 2: Basic Mechanics of a Cryptex

A cryptex might seem like an intriquate machine, and in some ways it is, but most of it is the same mechanism repeating itself in a row. Inside the cryptex, there is a long recess that is made out of a series of notches, every other notch (the discs without the letters) are locked into place, the notches on the discs with the letters can rotate though. The tube that sits in the cryptex has some keys or teeth. These keys will sit in the notches that are locked into place, and to pull the tube out, the notches must align to make one long recess where the keys can slide through. If it is a bit confusing the video will explain it a bit better. So as you can see the cryptex is actually fairly simple. Since the end pieces in the cryptex, also are locked into position the can be used to keep the whole thing together. The bars on the outside of the cryptex are the ones that keep the whole construction together, I later moved them to the inside of the cryptex to make it look nicer and so they could not be removed by force and then allow the cryptex to be opened without the keyword.

Step 3: Clicking Mechanism

As I wrote in the beginning of the instructables I had some problems with having to very precisely align the letters to open the cryptex and that bothered me, so I decided that I needed some kind of clicking mechanism so the letters would align themselves. I did that by adding a inward facing gear between the static and dynamic rings(the rings that can not turn and the ones that can, ie. the rings with and without the lettes) and then I also had a ring with a "spring" that would be able to bend down when the gear is turned in one direction but will lock the gear when turned in another direction, this gives it the clicking effect and also makes it more precise. The recess on the inside is made for 3mm. keys but I added 0.5 mm. on either side, to give it some tolerance. It also gives the cryptex a really nice tactile feeling when using it, and the sound is also very nice. I cut out some of the gear tooths to make a round surface where the inner part with the spring would turn, to make sure that the construction is concentric.

In hindsight it would have been better if the cryptex could be turned both ways.

Step 4: Design Features

On top of wanting to have a functioning cryptex, I also wanted one to have on my shelf at home, as a kind of conversation piece. I liked the look from the davince code, where the cryptex looks like a rolled up codex or scroll. So in the final design, I made the end pieces have a bigger diameter than the middle part, I also wanted to have some kind of indicator where the word has to be aligned, so I kept one of the crossbars from the first version, to have it as a display. As a last thing I also made the radius of the letters discs 1 mm larger, to get a better grip, but that also added a nice design feature that made the disc have kind og a checker pattern.

Step 5: Building the Cryptex

The cryptex is made out of laminated sheets of 3 mm. MDF, it in some ways mimicks the same way a 3D-printer works. The parts are laminated using normal fast setting PVA glue, the same stuff one would get in a craft store.

Step 6: Dynamic Disc

The dynamic discs are made out of 3 parts. The gear for the clicking mechanism, the middle part and the disc with the spring mechanism. Afterwards the letters are added. If the disc has to spell out the letter C, the letter C should be in the recess outside the notch where the key goes through, afterwards come D, E, F etc. in the counter clockwise direction, so when the disc is turned clockwise the next letter shown is the next in the alphabet. Then it goes all the way to Z and then from A to the start letter, in this case C. To make sure that the gear align correctly the spring disc is inserted and aligned so the notches for the key align.

Step 7: Static Disc

The static disc is made the same way that the dynamic disc is made, but without the letters. As simple as that.

Step 8: Inner Tube

Unfortunately I have no pictures of assemblying the inner tube, and there is not really that much to it, so hopefully the picture of the final part will do.

Step 9: Final Assembly

This is the most crucial step, after gluing these parts together, there is no going back. The most important thing to do, is to make sure that the discs are in the right order and sequence. The disc has to alternate between static and dynamic, and the letters has to be in the right order. The individual discs are made so they have an inner part on one side and an outer part on the other, this is the case for all the discs, when they are stacked the inner and outer parts will make the discs turn concentric and lock together so they can not be shifted. On the static discs there are finger joints on the inside, that will be mounted on 4 connectors, that also holds the end pieces together and lock all the discs in. The discs should be stacked so the recess aligns, then the assembly bars get some glue and are added on the inside, this is a difficult step because you do not want glue all over the inside of the cryptex, or it will get stuck.

Step 10: Conclusion

After making 3 versions, I ended up with a working, somewhat good looking cryptex. With the added bonus of the click effect. Though I would have liked to be able to turn the wheel in both directions, and there is a bit of twist in the structure, but that is due to the material and because I used glue instead of eg. screws.

Full Spectrum Laser Contest 2016

Second Prize in the
Full Spectrum Laser Contest 2016