Materials & Construction Guide
Shared materials and construction techniques for building the puzzles.
Shared Materials
| Material | Specification | Puzzles Used In | Source |
|---|---|---|---|
| Steel rod | 4mm diameter, mild steel | 1, 3, 5, 6, 8, 10 | Metal supplier / welding shop |
| Steel rod | 3mm diameter, mild steel | 8 (shuttle bar) | Metal supplier / welding shop |
| Braided cord | 5mm braided nylon (paracord 550 type III) | 1, 2, 3, 6, 7, 8, 9 | Outdoor / craft supplier |
| Braided cord | 4mm braided nylon | 10 | Outdoor / craft supplier |
| Braided cord | 3mm braided nylon | 4 | Outdoor / craft supplier |
| Welded O-rings | 40mm OD, 4mm wire | 4, 9 | Marine / rigging supplier |
| Welded O-rings | 50mm OD, 4mm wire | 1, 3, 6, 7 | Marine / rigging supplier |
| Welded O-rings | 55mm OD, 4mm wire | 10 | Marine / rigging supplier |
| Wooden balls | 25mm, drilled 6mm through-hole | 9 (cord stops), 10 | Craft supply |
| Wooden balls | 30mm, drilled 6mm through-hole | 7 (finial), 9 (cord stops) | Craft supply |
| Steel balls | 8mm solid | 6 (prong stops) | Hardware / bearing supplier |
| Hardwood | Maple or beech, various dimensions | 2, 7, 8, 10 | Lumber supplier |
| Wooden dowels | 10mm diameter, 80mm length | 8 (posts) | Craft supply |
| Cast acrylic | Clear, 120mm x 80mm x 60mm block | 9 | 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 |
Shared Construction Techniques
Bending Steel Rod
Use a rod bending jig or vise for consistent curves. For U-shapes (Puzzles 1, 6), mark bend points and bend around a mandrel of the desired inner radius. For ovals (Puzzle 5), 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 9): 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 | Ring OD | Must slide over | Must be stopped by |
|---|---|---|---|
| 1 | 50mm | 5mm cord | N/A |
| 3 | 50mm | 5mm cord | N/A |
| 4 | 40mm | 3mm cord | N/A |
| 6 | 50mm | 4mm prong rod | 8mm ball stops |
| 7 | 50mm | 20mm post | 30mm ball finial |
| 9 | 40mm | 5mm cord | 15mm tunnel diameter |
| 10 | 55mm | 4mm hoop rod | Window geometry |
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 6, 9, and 10, where dimensional tolerances are tight.