Research on diamond turning of large optical metal mirrors. Characteristics of single crystal diamond tools.

Decisions relating to suitable machining condition for single crystal diamond tools is essential to large optics diamond turning, because of tool wear over long cutting distances. Single point tools having curved edge are used for turning a concave mirror. The tested diamond tools have 2 mm and 10 mm of nose radius ; and the workpiece material is aluminium alloy. In accordance with increasing the cutting distance, thrust force is gradually increased by blanting of the cutting edge. However, the surface roughness of metal mirror is still good even after the cutting distance has reached 900 km, because of the burnishing effect by tool wear. The residual compressive stress occurs on the surface layer of a metal mirror after diamond turning. It is considered that the stress is connected with the nose radius and tool wear.