There are a few really great machines on the market for cutting keys using computer control. Companies such as Silca and Bianchi make it really easy to cut keys accurately and easy. They have great features such as built in code software and electronic probe functions. I would recommend to you to purchase these machines if you can afford them.
So the big question is why would you want to use a CNC milling machine to cut keys and is there any advantage to a commercially available machine??
Well the first advantage has to be the price. A CNC milling machine is much cheaper then any commercially available key cutting machine. Me personally it was the money issue that sent me down this track. I have been cutting keys on a CNC machine for some years now and it has cost me very little in setup costs. So hopefully my wins and failures can be of use to you and make it an easy and cheap project for anyone wanting a computerized key cutting machine.
Second big advantage is flexibility. The number of different types of keys you can cut using a CNC machine is just about endless. Different keys will require different clamps, etc for holding the key blank in position and you will require different techniques and code for your CNC key cutting machine. But using the one machine you can produce many different keys and because everything is programmable it is 100% flexible.
My main focus has been on Milled Keys, or track keys, but the list of different key types is growing. Most of the high security car keys are all 2 1/2 dimensioned milled keys. They are mostly milled at the same height with either 1 or 2 tracks. Each track having different depths to correspond with the combination of the lock.
Above is a a screen-shot of a wizard used to generate keys to code.