Precision grinding for rapid fabrication of segments for extremely large telescopes using the Cranfield BoX

Xavier Tonnellier; Paul Morantz; Paul Shore; Paul Comley

doi:10.1117/12.858806

19 July 2010 Precision grinding for rapid fabrication of segments for extremely large telescopes using the Cranfield BoX

Xavier Tonnellier, Paul Morantz, Paul Shore, Paul Comley

Author Affiliations +

Proceedings Volume 7739, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation; 773905 (2010) https://doi.org/10.1117/12.858806
Event: SPIE Astronomical Telescopes + Instrumentation, 2010, San Diego, California, United States

Abstract

An ultra precision large optics grinding machine, BoX®, was developed and produced at Cranfield University. BoX® offers a rapid and economic solution for grinding large off-axis aspherical and free-form optical components. Grinding high accuracy surfaces with low subsurface damage reduces subsequent polishing time. This efficient grinding process provides the capacity to grind 1.5 m parts. This paper presents an analysis of Astrositall® optical ground parts: a hexagonal 84 m radius of curvature mirror of 1 m across corners and an off-axis 350 mm diameter mirror. The 1 m hexagonal part is representative of segments under study for making extremely large telescope (ELT) segmented mirrors. The second part was machined off-axis to demonstrate free-form fabrication capability. These operations demonstrate the scalability of the rapid grinding process developed for large free-form optics. The use of an error compensation procedure improved an initial ground form accuracy to +/- 1 μm p-v over 1 metre surface. The results highlighted the effect of grinding parameters and machine dynamics on form accuracy and fabrication time.

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Xavier Tonnellier, Paul Morantz, Paul Shore, and Paul Comley "Precision grinding for rapid fabrication of segments for extremely large telescopes using the Cranfield BoX", Proc. SPIE 7739, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation, 773905 (19 July 2010); https://doi.org/10.1117/12.858806

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