Pocket Cryptex with Resettable 4-Digit Code

A pocket cryptex. Turn the four rings until the code sits on the reading line and the inner cartridge slides out. Every ring clicks into place on each of its 10 digits, so it always stops aligned. With any ring one digit off, it stays locked. The code is chosen at assembly and can be changed any time.

How it works

• The cartridge carries 4 teeth that stick out through a slot in the tube and sit inside a groove in each ring, so the rings spin freely but the cartridge cannot move.

• Each ring has one real gate. Only when all 4 gates line up with the slot can the teeth pass.

• Each ring also has 4 false gates: shallow notches that catch a tooth when you pull, so you can't find the code by feel.

• Clicks: each ring core has two flexible printed arms whose tips drop into 10 notches on the tube (9 notches plus the slot itself, cut to the same shape). On a digit the tips are free; between digits they press 0.45 mm on the tube and the arms flex.

• Each ring is two parts (core with the gate + dial with the digits) joined by 10 splines: slide the dial on at the digit you want and that is your code.

• The end collar is a bayonet: push down and twist 60°.

Details

• Closed: Ø44 × 73 mm. Storage: Ø18.8 × 68 mm, open at the inner end: pull the cartridge out to load it (a rolled note, a key, a SIM, a USB stick, a secret message).

• Lead-in chamfers on the tube, cartridge, cores, dials and collar, and 45° funnels on every gate, so the cartridge goes in and out without catching.

• Every overhang is 45° or less (bayonet lugs and grooves included): no supports. Tube upright, cartridge head-down, rings and collar flat.

• Plate 1 (tube, cartridge, collar, 4 cores): 2 h 13 min, 48 g. Plate 2 (4 dials, digits inlaid in a 2nd colour): 1 h 52 min, 29 g. A1 mini, 0.4 mm nozzle, PLA.

• Gates are 24° wide; the clicks hold each ring within about ±1° of the line, and one digit off (36°) blocks.

How it was checked

Collision volumes in OpenSCAD (manifold): closed with the rings scrambled on digits, no part touches another (0 mm³). With the code set, the cartridge slides the full 69 mm out without touching anything, also with the rings ±3° off and the cartridge turned ±1.5° in its slot. Clicks: on all 10 digits of all 4 rings the arm tips touch nothing; half way between digits they overlap the tube by 6.4 mm³ in total (two tips, 0.45 mm deep), and only the tips; each arm has 0.68 mm of room to flex. Controls that must collide, and do: scrambled, pulling 2 mm (27 mm³); one ring one digit off (15 mm³); a tooth caught in a false gate locks at 2 mm; a ring 10° off trips the cartridge; a tube without notches jams the tips on a digit (6.4 mm³); the closed collar cannot lift 2 mm. The bayonet collar goes in and turns 60° without collisions. Each printed part was checked for overhangs over 45° (none) and for being one single body.

OpenSCAD source included: change the code, ring count or sizes.

About this design

Designed with AI assistance and checked in code before release (see above). Pictures are 3D renders and the slicer preview, not photos. Not printed yet: the click strength depends on your printer, so makes and feedback are very welcome.

Español

Criptex de bolsillo: cada anillo hace clic en cada cifra y se queda alineado. Con las 4 cifras en la línea, el cartucho sale; con una cifra mal, no. El código se elige al montar y se puede cambiar. Sin soportes. Placa 1: 2 h 13 min, 48 g; placa 2: 1 h 52 min, 29 g.

العربية

صندوق سري بأربعة أرقام: كل حلقة تصدر نقرة عند كل رقم وتبقى في مكانها. عند ضبط الرمز يخرج الأنبوب الداخلي، وبرقم خاطئ واحد يبقى مقفلا. يمكن تغيير الرمز عند التركيب. بلا دعامات.