Can you affix the heavy chain to an immobile object when you use your action to set a Hunting Trap (PHB p. 152), or is it just the opening of the teeth that takes an action? The text says:
When you use your action to set it, this trap forms a saw-toothed steel ring that snaps shut when a creature steps on a pressure plate in the center. The trap is affixed by a heavy chain to an immobile object, such as a tree or a spike driven into the ground.
A creature that steps on the plate must succeed on a DC 13 Dexterity saving throw or take 1d4 piercing damage and stop moving. Thereafter, until the creature breaks free of the trap, its movement is limited by the length of the chain (typically 3 feet long).
If it's not all done in an action, then can you use the trap without the chain? How long does it take to affix the chain? Does this include driving the spike into the ground?