Fast manufacturing of E-ELT mirror segments using CNC polishing

C. Gray, I. Baker, G. Davies, R. Evans, N. Field, T. Fox-Leonard, W. Messelink, J. Mitchell, P. Rees, S. Waine, D. D. Walker, G. Yu

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

20 Citations (Scopus)


We report on the first-ever demonstration of grinding and polishing full-size, off-axis aspheric, mirror segments as prototypes for an extremely large telescope, processed entirely in the final hexagonal shape. We first describe the overall strategy for controlling form and mid spatial frequencies, at levels in the vicinity of <10nm RMS surface. This relies first on direct CNC grinding of the base-form of these 1.4m segments, using the Cranfield BoX™ machine. The segments are then mounted on a custom designed (Optic Glyndwr Optoelectronic Engineering Group) three segment hydraulic support, and CNC polished on a Zeeko IRP 1600 machine using a variety of custom tooling. We overview the fullaperture and sub-aperture metrology techniques used to close the process-loop and certify quality, all of which operate with the segment in-situ on the IRP1600. We then focus on the pristine edge-definition achieved by the combination of tool-lift and smoothing operations; results never previously demonstrated on full-size pre-cut hexagonal segments. Finally, the paper discusses the feasibility of scaling the process to deliver 931 segments in seven years, as required for the E-ELT project.

Original languageEnglish
Title of host publicationOptical Manufacturing and Testing X
Publication statusPublished - 28 Nov 2013
Externally publishedYes
EventOptical Manufacturing and Testing X - San Diego, United States
Duration: 26 Aug 201327 Aug 2013
Conference number: X (Link to Conference Details )


ConferenceOptical Manufacturing and Testing X
Country/TerritoryUnited States
CitySan Diego
Internet address


Dive into the research topics of 'Fast manufacturing of E-ELT mirror segments using CNC polishing'. Together they form a unique fingerprint.

Cite this