An industrial diamond turning production machine acquired from the former Rank Taylor Hobson company has been renovated in-house with the installation of a new control-system. The machine was used at Taylor Hobson for producing glass aspherics for precision zoom lenses, and for machining infrared materials etc. Whilst the Taylor Hobson process involved post-polishing with a bag polisher, its was reported that the machine had exhibited ductile regime cutting on glass with very fine cuts.

 The machine is unique in being of the Z-theta configuration.

The work-piece is held in a collet that rotates on a spindle in an air-bearing. The tool is mounted on a rotating table, so that it traverses in an arc across the work-piece, thereby naturally producing a concave or convex sphere. The work-piece spindle can also be translated axially over 10mm with 5 nanometre resolution on another air-bearing mechanism. This permits the production of an aspheric form (and, indeed, a flat if required).

The key advantage of the machine configuration is that, with most surfaces, the diamond always presents essentially the same orientation to the work-piece surface, mitigating against the effects of variations in tool-wear with different crystal orientation.

The interest in the Laboratory in this facility is three-fold:

• The facility provides a capability for machining aspherics of varying degrees of surface finish for subsequent computer controlled polishing.

• The machine can produce precision references in mechanical interfaces for instrumentation.

• The facility provides a research platform in its own right. It is currently being used for research in turning aspherics in optical plastic materials. This work is being undertaken by a visiting scientist Dr Larvrynenko from the former Soviet Union (sponsored by the Royal Society), in collaboration with Prof. K. Puttick (Surrey Univ.) It is planned that the research programme will move on to diamond tool wear and other aspects of diamond machining of glassy materials.