The University of Arizona

MMT Polishing

During 1995 the mirror blank's back surface was ground and polished mechanically flat (to ± 100 microns) to relieve stresses and to provide a flat surface to attach the loadspreaders for polishing, testing, and ultimately supporting the mirror in the telescope. The mirror was then inverted, placed on an array of specially designed hydraulic support actuators. The faceplate was then milled to within a few thousandths of an inch of its final shape.