Enigma Cipher Machine

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A rotor cipher machine you print. Push the key and the three rotors step like the ones in a real Enigma, double step included. Then follow your letter through the rings: in through the three rotors, round the reflector in the middle and back out to the outer ring, which gives the cipher letter. The rotors carry the wiring of rotors I, II and III of the Enigma I and the reflector is reflector B, so a message you encrypt on it decrypts on any Enigma I simulator set to the same start letters (rings at A, no plugboard), and the other way round. No electronics: the wiring is printed on the rings.

• 13 printed parts

• 21 × 20 × 2 cm assembled (L × W × H)

• ≈ 0.3 kg filament in total

• 196 mm across, for the base and the outer ring: a 200 × 200 mm bed

Parts

Base: The body: a pocket for the key lever under the rotors, the post the lever turns on and three printed springs that click the rotors from letter to letter. Four holes underneath for the outer ring's screws.

• Size: 196 × 196 × 8 mm

• Print: Flat side down. No supports.

• Filament: ≈ 125 g

Key lever: Push the key to the right and the lever turns all three pawls by one letter. Pawl 1 always steps rotor III. Pawls 2 and 3 can only reach the next rotor through a notch in the rotor outside it, which is how the carry and the double step work.

• Size: 121 × 51 × 13 mm

• Print: Flat, as in the file. PETG keeps the sprung pawls springy longest; PLA works.

• Filament: ≈ 9 g

Rotor III: The fast rotor, on the outside. 26 ratchet teeth underneath, and a notch that lets rotor II step when this one moves on from V.

• Size: 168 × 168 × 5 mm

• Print: Face up. Load it together with its letters as one object for a second colour.

• Filament: ≈ 35 g

Rotor III letters: The alphabet on its outer track and the wiring of rotor III on its inner track.

• Size: 161 × 161 × 1 mm

• Print: With the rotor, as a second part, or swap filament at 5.0 mm.

• Filament: ≈ 0 g

Rotor II: The middle rotor. Its notch at E lets rotor I step and makes rotor II itself step twice in a row, as in the real machine.

• Size: 134 × 134 × 5 mm

• Print: Face up, with its letters.

• Filament: ≈ 27 g

Rotor II letters: The alphabet and the wiring of rotor II.

• Size: 127 × 127 × 1 mm

• Print: With the rotor, or swap filament at 5.0 mm.

• Filament: ≈ 0 g

Rotor I: The slow rotor, next to the reflector. It has no notch: nothing comes after it.

• Size: 100 × 100 × 5 mm

• Print: Face up, with its letters.

• Filament: ≈ 18 g

Rotor I letters: The alphabet and the wiring of rotor I.

• Size: 93 × 93 × 1 mm

• Print: With the rotor, or swap filament at 5.0 mm.

• Filament: ≈ 0 g

Outer ring: The fixed ring with the letters you type and read. Four M3 × 8 hold it from under the base, and its lip keeps the rotors down.

• Size: 194 × 194 × 5 mm

• Print: Face up, with its letters.

• Filament: ≈ 34 g

Outer ring letters: A to Z and the index at the top, where you read the start letters.

• Size: 187 × 182 × 1 mm

• Print: With the ring, or swap filament at 5.0 mm.

• Filament: ≈ 0 g

Reflector: Reflector B, in the middle. Its hex sits on the post so it can't turn, and its lip holds rotor I down.

• Size: 69 × 69 × 6 mm

• Print: Face up, with its numbers.

• Filament: ≈ 14 g

Reflector numbers: The numbers 1 to 13, each twice: the two spokes with the same number are wired together.

• Size: 64 × 62 × 1 mm

• Print: With the reflector, or swap filament at 5.0 mm.

• Filament: ≈ 0 g

Pointer: Turns over the dial on the centre screw, with a window along one spoke to keep your place.

• Size: 106 × 16 × 3 mm

• Print: Upside down, as in the file.

• Filament: ≈ 2 g

What else you need

• One M3 × 12 screw and a washer: it holds the pointer and the reflector on the post.

• Four M3 × 8 screws for the outer ring, from under the base. They cut their own thread in the plastic.

• A pencil and paper for the letters you get.

Print settings

• 0.2 mm layer height

• 3 walls

• 15% infill

• 5.0 mm filament change for the letters, unless you print them as a second part

For a 0.4 mm nozzle. Filament amounts are estimates for these settings.

How to build it

1. Print the parts: Nothing needs supports. For letters in a second colour, load each rotor, the outer ring and the reflector together with its letters file as one object, or pause at 5.0 mm and swap filament. Clean any elephant's foot off the undersides of the rotors: they slide on the base.

2. Lever: Lay the lever in its pocket in the base, the hub over the post and the key sticking out at the front. It should swing freely between its two stops.

3. Rotors: Drop in rotor I, the smallest, then rotor II, then rotor III. Each one's lip lies over the edge of the one inside it. Turn each by hand: it should click from letter to letter.

4. Outer ring and reflector: Put the outer ring on with A at the top (the screw holes only line up one way) and screw it on from below with four M3 × 8. Set the reflector on the post, the pointer on top, and screw both down with the M3 × 12 and a washer, just tight enough that the pointer stays where you leave it.

5. Set the key: Turn the rotors so the three letters under the index at the top spell your key, from the inside out: rotor I, II, III. The animation starts at A D U.

6. Press the key: Before every letter, push the key to the right until it stops and let it back. Rotor III moves on one letter, and now and then the others move too, just as when you press a key on the real machine.

7. Follow the letter in: Find your letter on the outer ring. Go in along its spoke to the outer track of rotor III, read the letter there and find the same letter on the inner track of rotor III. From that spoke go on in to rotor II and do the same, then rotor I.

8. Reflector and back out: In the reflector, go to the other spoke with the same number. Then go back out: read the letter on a rotor's inner track and find it on its outer track, which is in alphabetical order, rotor by rotor. The letter on the outer ring is your cipher letter.

9. Decrypt: Set the same key and type the cipher text the same way: you get the message back. Any Enigma I simulator set to rotors I-II-III, reflector B, rings A-A-A and no plugboard gives the same letters.

Small parts and screws: keep them away from small children.

More

3D viewer, colour preview and the full guide: https://shapekit.cc/enigma-machine.html

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