The CNC timing pulley version is the simplest version to make requiring just one bore thru and a shallow counterbore plus setscrews in the pulley. It's the first one that I made. It simply drops onto the spindle shaft and is held in place by the setscrews. It does eliminate the quill action from the spindle but for a CNCed mill this is not usually a problem anyway. The Z axis does all the movement reqired.