I know this has been done before quite a few times however whilst I was doing research I found photos online useful so here goes, firstly the mechanical stuff.
All acme screws on the machine have been replaced with ball screws, 16mm on X and Y and 25mm on the Z(Knee) the Quill has been left alone so the machine could still have manual function besides the rack and pinion had far to much play. First comment would be buy the best you can afford the Z axis was from Zapp and appears to be a quality item the other two were from another supplier who advertised quality but once they were fitted and tested the backlash in the nut became obvious, lesson learnt. Easy enough to turn custom ends on the stock scews with the right tips.
All support bearings replaced with preassembled and preloaded ball screw support assembly's these were quite easy to set into a machined pocket in the original (yellow) bearing supports.
The Z axis on the Warco goes into a bearing assembly which is removable so with a little machining this support block was made to accept two taper roller bearings , the ball screw then passes through these bearings through the gear and terminates with a locknut as before, below the bearing assembly the ball screw was machined to accept a taper lock pulley so the motor could drive the ball screw direct without using the manual gear system as this has far to much backlash and potential for play.
Once completed this machines has been tested and calibrated using a Renishaw ball bar which showed the best I could achieve was a positional tolerance of 40 micron in a 8" circle and a best circularity of 35micron again on a 8" circle. For those that don't know the Renishaw ball bar is a device made to be able to test machine tools for accuracy and repeatability they cost lots (15K plus) and need training in order to use correctly fortunately due to my profession I am fortunate to have access to such goodies.
I will try and post up now some photos taken during the build and any questions ask away I will drop in here from time to time and am willing to help where I can......