Walker, D.D., Beaucamp, A., Dunn, C., Evans, R., Freeman, R., Morton, R., Wei, X. and Yu, G. (2008) Active Control of Edges and Global Microstructure on Segmented Mirrors. SPIE - International Society for Optical Engineering. Proceedings. ISSN 0277-786X

In this paper we address two interrelated issues important to primary mirror segments for extremely large telescopes - edge-control, and the detailed topography over the segment surface. Both affect the intensity and distribution of stray light and infrared emissivity. CNC polishing processes typically deploy spiral or raster tool-paths, tending to leave repetitive features. We compare and contrast two novel families of pseudo-random tool-paths for Precessions CNC polishing. We then show how CNC control of the three-dimensional tool-path can optimize edge-profiles. Finally, we demonstrate fluid-jet polishing used to clean up residual edge defects.