Citation:
Xavier Tonnellier, Paul Morantza, Paul Shorea,
and Paul Comley. Precision grinding for rapid fabrication of segments for extremely large
telescopes using the Cranfield BoX. Proceedings of SPIE Modern Technologies in Space- and Ground-based Telescopes and Instrumentation,
Sunday 27 June 2010, San Diego, California, USA Vol. 7739, 773905 (2010). Eds. Eli Atad-Ettedgui, Dietrich Lemke.
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 t
