Jigsaw puzzle pieces and tunnelling shield: what they have in common

1. Step 1. Jigsaw puzzle pieces — is part of — Jigsaw puzzle. Cardboard pieces with tabs and slots.
2. Step 2. Jigsaw puzzle — is made of — Wood pulp. Cardboard.
3. Step 3. Wood pulp — is used in — Paper machine. The raw material.
4. Step 4. Paper machine — works like — Conveyor belt. Fourdrinier’s endless wire mesh moves like a conveyor belt, forming the web of paper.
5. Step 5. Conveyor belt — is part of — Tunnel boring machine. Spoil is removed by a conveyor.
6. Step 6. Tunnel boring machine — evolved from — Tunnelling shield. A development of the tunnelling shield.

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