Two-stage Cryptex: CAD Design

It is a truth universally acknowledged that raccoons like puzzles. Raccoons like, in fact, touching all things:

raccoon (n.) 

also racoon, c. 1600, arocoun, from Algonquian (Powhatan) arahkun, from arahkunem "he scratches with the hands." Early forms included Capt. John Smith's raugroughcum. In Norwegian, vaskebjørn, literally "wash-bear."

Disgusting.

Whether I like it or not, I have long suffered (like, for two whole years) an excess of raccoons and abundant inevitable raccooning from my boyfriend, who is absolutely three raccoons in a trenchcoat. And we both love puzzles. One of our first dates was an escape room, which, while having the possibility of turning out horribly, we absolutely destroyed. He introduced me to Myst via Steam gift while I was bedridden after surgery, and I in turn introduced him to the style of puzzle hunts, e.g. MIT Mystery Hunt. For my birthday/christmas last year, he gave me an ingenious Japanese puzzle box, inside which he had hidden a puzzle hunt that he himself wrote. Thus, I was inspired to create my own physical fiddly puzzle box, complete with puzzles and a small gift inside, to satisfy both raccooning and puzzling tendencies. But a single puzzle to fiddle with was too easy, and so I began to investigate a double-stage puzzle box, resulting in the design of this two-stage cryptex.

SolidWorks model 

The word "cryptex" was coined by Dan Brown in his novel, The Da Vinci Code, as a neologism portmanteau from kryptos and codex. It referred to a stone and brass cylinder with endcaps and discs that had every letter of the alphabet represented, and works much like a word combination lock. Once the user aligns the letters into the correct word, the inner tube can be pulled out to reveal the contents, or, in the case of my two-stage cryptex, an additional tube inside that requires re-solving of the cryptex with a different answer to release the final contents. Many designs for cryptexes (cryptices?) are available online, but I could only find one example of a two-stage cryptex, called a nested cryptex, starting from the low, low price of $3000. And in a foul twist of transitive property, love can't buy money any more than money can buy love. With the help of the pictures from the Nevins site above and this useful teardown from a fellow escape room enthusiast, I reverse-engineered the locking mechanism and designed my own two-stage cryptex.

First stage of the cryptex solved and removed.

An explanation for the divergent terminology: the nested cryptex from Nevins is literally a cryptex inside of a cryptex. I wanted to make an easier and more elegant solution, where the same dials from the outer chamber were used to solve for the inner chamber release as well. This resulted in the half-shell outer chamber, in order to allow the teeth of the inner chamber, offset 90 degrees from the teeth of the outer, to have access to the same dial spacing. Because this means double-solving the same cryptex, I decided that two-stage was a more apt descriptor for this puzzle box.

Internal structure of rings and spacers

Inside of the cryptex casing with stages removed

The lettered rings rotate freely around the inner chamber, but only one fully correct combination will allow the stages of the cryptex to pull loose. The central casing was designed to be machined from a 3" OD piece of aluminum tubing, with two longitudinal slots for the keyways on the chambers and two radial slots for the retaining ring at the open end to keep all of the rings and spacers constrained. 

Central chamber of the cryptex

Closeup of the retaining ring

Retaining ring

Due to the precision needed to align the letters properly, each side has a retaining ring with an embedded marker (the small hexagons with triangles) to help line up the tick marks on either side of the lettered rings. I debossed all of the symbols and letters, knowing that I was going to 3D print all of the lettered and retaining rings. 

Marker/retaining ring for the closed end

The innermost chamber is a smaller diameter than the outer chamber in order to fit concentrically into the casing, so there is a bottom lip to maintain concentric alignment. The outer end also has a lip; this way, once the first stage is solved, it can't be pulled out all the way and will catch on the lip, forcing the user to solve the cryptex once more in order to pull out the inner chamber along with the outer chamber. The second stage of the cryptex must be solved while the first stage has already been pulled out, in order to not interfere with the locking mechanism.

Innermost chamber (second stage) of the cryptex

The outer chamber thus has a corresponding lip on the bottom end, so that it will catch on the lip on the inner chamber. The top end of the outer chamber is just a solid circle here, because I needed some way to attach it to the aluminum endcaps.

Outer chamber (first stage) of the cryptex

The lettered rings are aligned with the lower ridges on the keyways on the chambers. Note that each ring didn't just have a keyway under the correct letters. Because the second stage relies on the same physical markers for alignment by the user, the keyways for the second stage must instead be ninety degrees offset from the second stage solution letters, so that they line up with the keyway for the second stage when the letters are aligned at the keyway of the first stage (where the indicators are located).

The last lettered ring of the cryptex, with first and last solutions being "S" so the second stage key slot must be ninety degrees offset.

Finally, I designed aluminum spacer rings, intended for waterjet or lasercutting fabrication, as spacers between the lettered rings, matching with the aluminum endcaps which served as grip. The spacer rings are rotationally constrained with flanges that seat into the axially milled slots along the casing, and include a key slot for the ridges atop the chambers.

This project was the first time I ever finished a full CAD model of the thing I was intending to build before I...went and built it. Having a CAD program made this entire design process vastly easier, but there were still a lot of difficulties translating my ideal cryptex into the physical product, only some of which could have been mitigated if I had been smarter about the CAD. I'll talk about those in part 2, the follow-up to this post.

P.S. If anyone wants the CAD files, I can be convinced to provide them, with the caveat that I had to make many changes after receiving the physical parts and I can only remember some of these changes to advise on improvements if you want to make your own version. And, of course, the letter rings will have to be modified to provide your custom answers :]