This will explain the process I went through to copy a key with a vice, a file and patience.
Step 1: Setting up
You will need to clamp the original and blank together in the vice in a way that you can use the original as a pattern for the duplicate. Be sure to have the entire key lined up perfectly and tighten the vice.
*You can destroy the original in the next step, so be sure you already have a (professional)copy of the original if its a critical key*