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After printing the box, carefully pry the hinges loose of any fused spots. You may need to wiggle the box walls for a while to loosen them enough for them to tip and fall easily on their own, especially if you're using a glitter filament. You can also try applying some silicone lubricant to the hinges to help things along.
Assembly is simple; push the lock cylinder through the lid from underneath and glue the bow into it on the top side. Careful not to spill the glue and glue everything to the lid! Rotate the lock so the blades point the corners, lift up the box walls and push in the lid. Then rotate the lock 45 degrees to lock the present.
The bow and lock has a hole for a string or ribbon if you want to hang it.