Technologies for producing segments for Extremely Large Telescopes

We describe progress on a novel process-chain being used to produce eight 1.4m hexagonal segments as prototypes for the European Extremely Large Telescope - a Master Spherical Segment as a reference, and seven aspheric segments. A new pilot plant integrates a bespoke full-aperture test-tower designed and built by OpTIC Glyndŵr, with a Zeeko 1.6m polishing machine. The process chain starts with aspherising hexagonal segments on the Cranfield BoX grinder, followed by smoothing, corrective-polishing and edge-rectification using the Zeeko CNC platform. The paper describes the technology and progress, and anticipates how the process-chain is expected to evolve through the seven segments to increase both process-speed and surface-quality.