... The plug-plates for the Sloan Digital Sky Survey are drilled with the plate elastically deformed over a convex mandrel and with the sky-facing side away from the mandrel. ... The deformation of the plug-plate by the drilling mandrel and the plug-plate cartridge causes radial distortion of the plate that must be anticipated by the computer numerical controlled (CNC) drilling program so that the end of each fiber optic is positioned correctly on the focal surface by the plug-plate. ...