Materials & Construction Guide
Shared materials and construction techniques for building the puzzles.
Puzzle numbers in this guide are display numbers — the series order (1–20) used in the README and on the site — not the frozen module filenames.
Arc 5 (Puzzles 18–20): the 3D-printed carriers — the ring stands, the tangle frame with its ball handles, and the mold board with its integral bridges — are still being finalized, and their parametric print models are forthcoming (the OpenSCAD sources for Arc 5 are deferred). The cord, ring, and raw-material specifications below are stable and buildable now; the printed parts are listed with their intended dimensions and flagged as forthcoming.
Shared Materials
| Material | Specification | Puzzles Used In | Source |
|---|---|---|---|
| Steel rod | 4mm diameter, mild steel | 1, 3, 6, 7, 12 | Metal supplier / welding shop |
| Steel rod | 3mm diameter, mild steel | 10 (shuttle bar) | Metal supplier / welding shop |
| Braided cord | 5mm braided nylon (paracord 550 type III) | 1, 2, 3, 7, 8, 10, 11, 20 | Outdoor / craft supplier |
| Braided cord | 4mm braided nylon (two-color pair for 19) | 12, 18, 19 | Outdoor / craft supplier |
| Braided cord | 3mm braided nylon | 4 | Outdoor / craft supplier |
| Welded O-rings | 40mm OD, 4mm wire | 4, 11 | Marine / rigging supplier |
| Welded O-rings | 50mm OD, 4mm wire | 1, 3, 7, 8 | Marine / rigging supplier |
| Welded O-rings | 55mm OD, 4mm wire | 12 | Marine / rigging supplier |
| Welded O-rings | 80mm OD, 6mm wire (68mm aperture) | 18 (rigid rings ×2) | Marine / rigging supplier |
| Wooden balls | 25mm, drilled 6mm through-hole | 12 (path-constraint ball) | Craft supply |
| Wooden balls | 30mm, drilled 6mm through-hole | 8 (finial), 11 (cord stops) | Craft supply |
| Steel balls | 8mm solid | 7 (prong stops) | Hardware / bearing supplier |
| Hardwood | Maple or beech, various dimensions | 2, 8, 10, 12 | Lumber supplier |
| Wooden dowels | 10mm diameter, 80mm length | 10 (posts) | Craft supply |
| Cast acrylic | Clear, 120mm x 80mm x 60mm block | 11 | Plastics supplier |
| Chrome-tanned leather | 2mm thick, 300mm x 25mm strip | 4 | Leather craft supplier |
| Rivets | Small brass or copper | 4 (Mobius band join) | Hardware supplier |
| 3D-printed PETG | Ring stands ×2 (18); 170mm square tangle frame + 16mm ball handles ×4 (19); ~200 x 120 x 14mm mold board with integral 7mm bridges (20) — print models forthcoming | 18, 19, 20 | FDM 3D printer (SCAD deferred) |
| Heat-shrink sleeve | Two contrasting colors, cord ID bands | 20 (loop identification) | Electronics / hardware supplier |
Shared Construction Techniques
Bending Steel Rod
Use a rod bending jig or vise for consistent curves. For U-shapes (Puzzles 1, 7), mark bend points and bend around a mandrel of the desired inner radius. For ovals (Puzzle 6), use an oval form or bend freehand, ensuring both sides are symmetric before welding the closure.
Welding
All steel joints should be MIG or TIG welded. Grind all welds flush and smooth — any burr or rough spot will catch cord or rings and make the puzzle frustrating rather than challenging. Test that rings slide freely over all welded joints.
Cord Preparation
- Cut cord with a hot knife or heated blade to prevent fraying
- Seal all cut ends with a lighter flame (melt and press flat)
- For closed loops: splice ends using a fid, or tie a fisherman's knot and seal with adhesive
- For fixed ends: thread through drilled holes and tie figure-eight stopper knots on the inside, optionally sealed with a drop of CA glue
Drilling
- Holes in steel rod tips (Puzzle 1): use a 1.5mm drill bit on a drill press; clamp the rod securely
- Through-tunnels in acrylic (Puzzle 11): use a 15mm Forstner bit on a drill press at slow speed with cooling fluid to prevent melting; polish tunnel interiors with progressively finer sandpaper (400 → 800 → 1200 grit)
- Holes in wooden paddles (Puzzle 2): use a 20mm Forstner bit; sand edges of hole smooth
Wood Finishing
Sand all wooden components to 220 grit minimum. Apply a thin coat of beeswax or tung oil for smooth cord sliding. Do not use polyurethane — it creates too much friction for cord puzzles.
Ring Sizing
The critical relationship in most puzzles is ring inner diameter vs. the elements it must pass over or be stopped by:
| Puzzle | Name | Ring OD | Must slide over | Must be stopped by |
|---|---|---|---|---|
| 1 | The Gatekeeper | 50mm | 5mm cord | N/A |
| 3 | The Prisoner's Ring | 50mm | 5mm cord | N/A |
| 4 | Mobius Snare | 40mm | 3mm cord | N/A |
| 7 | Devil's Pitchfork | 50mm | 4mm prong rod | 8mm ball stops |
| 8 | The Ferryman's Knot | 50mm | 20mm post | 30mm ball finial |
| 11 | Genus Trap | 40mm | 5mm cord | 15mm tunnel diameter |
| 12 | The Hopf Paradox | 55mm | 4mm hoop rod | Window geometry |
| 18 | The Whitehead Waltz | 80mm (68mm aperture) | 4mm cord (bight of 4 strands) | N/A (seated in stand) |
Prototyping Advice
Build Puzzles 1 and 2 first — they use the simplest materials and validate your cord/ring sizing. Before building each puzzle, test the critical dimensional relationships with scrap materials:
- Can the ring slide freely where it should?
- Is the cord long enough for the solution moves but short enough to maintain the constraint?
- Do ball-stops actually stop the ring, or does it slip past?
- Does the cord slide smoothly through all holes and tunnels?
Expect to iterate 2-3 times on Puzzles 7, 11, and 12, where dimensional tolerances are tight.