A laser or a sharp blade will then be used in order to cut the the plane key, but it will be moving in alignment with your other key. This way then your key is being used as a 'stencil' almost for the new key and providing the outline for it.

            One thing to bear in mind is that there are certain keys that require specific key cutting techniques. For example a 'sidewinder' key cannot be cut using a normal key cutting machine. The reason for this is that here the teeth are indented into a groove that runs along the inside of the key rather than being on the outside edge. This means that there is no edge to use as a stencil. Similarly you cannot use regular key cutting if the key says 'DND' on it. This stands for 'Do Not Duplicate' and is an indication to the key cutting service not to cut the key.

            However presuming that your key is cut-able it is apparent why you are not able to perform key cutting on your own, and why it is necessary to use a key cutting service.