Tunnel boring machine and saw: what they have in common

1. Step 1. Tunnel boring machine — has part — Conveyor belt. Spoil is removed by a conveyor.
2. Step 2. Conveyor belt — works like — Escalator. An escalator is a conveyor with steps.
3. Step 3. Escalator — has part — Roller chain. A chain pulls the steps.
4. Step 4. Roller chain — is part of — Chainsaw. The cutting chain is a roller chain with teeth.
5. Step 5. Chainsaw — evolved from — Saw. A mechanized saw.

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