New results from the Precessions polishing process scaled to larger sizes

David D. Walker; Anthony T. H. Beaucamp; David Brooks; V. Doubrovski; Matthew D. Cassie; C. Dunn; Richard R. Freeman; Andrew King; M. Libert; Gerry McCavana; Roger Morton; David Riley; John Simms

doi:10.1117/12.553044

24 September 2004 New results from the Precessions polishing process scaled to larger sizes

David D. Walker, Anthony T. H. Beaucamp, David Brooks, V. Doubrovski, Matthew D. Cassie, C. Dunn, Richard R. Freeman, Andrew King, M. Libert, Gerry McCavana, Roger Morton, David Riley, John Simms

Author Affiliations +

Proceedings Volume 5494, Optical Fabrication, Metrology, and Material Advancements for Telescopes; (2004) https://doi.org/10.1117/12.553044
Event: SPIE Astronomical Telescopes + Instrumentation, 2004, Glasgow, United Kingdom

Abstract

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.

Citation Download Citation

David D. Walker, Anthony T. H. Beaucamp, David Brooks, V. Doubrovski, Matthew D. Cassie, C. Dunn, Richard R. Freeman, Andrew King, M. Libert, Gerry McCavana, Roger Morton, David Riley, and John Simms "New results from the Precessions polishing process scaled to larger sizes", Proc. SPIE 5494, Optical Fabrication, Metrology, and Material Advancements for Telescopes, (24 September 2004); https://doi.org/10.1117/12.553044

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