New results from the Precessions polishing process scaled to larger sizes

D. D. Walker, A. T.H. Beaucamp, D. Brooks, V. Doubrovski, M. Cassie, C. Dunn, R. Freeman, A. King, M. Libert, G. McCavana, R. Morton, D. Riley, J. Simms

Research output: Contribution to journalConference articlepeer-review


The Precessions process uses an inflated membrane-tool that delivers near-Gaussian polishing spots. The tool-motion over the part can be constructed to preserve an aspheric form whilst removing damage from preceding processes, or control the form through a tool-path prescribed by numerical optimization. The process has previously been validated on surfaces up to 200mm diameter and used extensively in industrial environments. In this paper we report the first trials on a substantially larger part - a 500mm diameter f/1 ellipsoidal mirror - as part of the UK's technology-development for Extremely Large Telescopes. We draw attention to subtle problems that have arisen along the way. We also report on developing the process for free-form surfaces, in contrast to the axially-symmetric parts worked hitherto. The paper concludes with an assessment of the lessons learnt from the experiments, as they may impact on realization in a practical ELT segment fabrication facility.

Original languageEnglish
Pages (from-to)71-80
Number of pages10
JournalProceedings of SPIE - The International Society for Optical Engineering
Publication statusPublished - 2004
Externally publishedYes
EventOptical Fabrication, Metrology, and Materials Advancements for Telescopes - Glasgow, United Kingdom
Duration: 2004 Jun 242004 Jun 25

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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