Mine was done with servos and geckos with 5/8" Roton screws on the X&Y axis with the existing quill down feed being the mechanism used on Z. There was additional work done to reduce the backlash on the quill to an acceptable level. Power supply was home built un-regulated using a microwave transformer that was rewound. It was also wound with an additional winding for the 5V and 12V supplies.
The biggest problems over the years have been from Operator error!
Art
AKA Country Bubba (Older Than Dirt)