Cranfield ‘spin-out’ signs up ultra-precision machine tool maker Hembrug for telescope optics grinding machine

The BoX (Big OptiX) is a claimed unique machine, specifically designed for grinding large optics to highest accuracy, in the shortest possible time. The design maximises stiffness at the grinding wheel, such that material removal rates of up to 200 mm3/sec are possible, allowing the grinding time of a 1.5 m mirror segment to be shortened from 100s of hours down to 20 hours. Polishing times are also shortened, by a factor of 10, due to reducing levels of induced sub-surface damage (SSD) 3 - 5 micron. The BoX machine therefore brings a solution to shorten the whole process chain of large optics fabrication and enables free-form optics generation to be achieved with unprecedented accuracy levels. Large optics can be found in the latest generation extremely large telescopes (ELT) and high power laser systems. For example, before 2018, a demand of almost 1,000 1.5 m mirror segments has to be fulfilled to produce the ESO E-ELT ground based telescope. The market for grinding large optics is a niche but growing market, with an annual need of several machines a year. Hembrug's product portfolio currently consists mainly of hard turning machines for ultra-precision finishing, employing hydrostatic technology. BoX is fully oil-hydrostatic in all rotary and linear axes, including the grinding spindle, while linear axes employ the latest generation linear motors. Hembrug will use standard components where possible for the BoX. "Hembrug has worked closely with Cranfield University in establishing the initial BoX prototype machine," explained Paul Shore, managing director, Loxham Precision, who sees the licence agreement with Hembrug as a natural one. "Hembrug possess the necessary high precision machine tool technology together with a service and support infrastructure to ensure customer confidence in acquiring the BoX ultra precision machines. Through this agreement, Loxham Precision will provide Hembrug free-form optics tool path generation software and necessary optical grinding expertise." And he highlighted that the BoX concept is already well proven : "The prototype BoX has already produced numerous metre size free-form mirrors and optics; including 1.5 m sized mirror segments for the ESO E-ELT ground based telescope." See also previous related Machinery articles Polished UK performance Big science drives innovation Stellar precision Space age metrology