This paper investigates the impact of diamond crystal type on single point diamond turning of single crystal silicon oriented at the <111< direction. The sample has a diameter of 85 mm with a concave base radius of curvature of 291 mm. The tools are made of single crystal diamond formed naturally (hereby referred to as natural diamond) and under lab controlled highpressure high-temperature conditions (hereby referred to as synthetic diamond). The tools have similar geometries of 0.5 mm nose radius, -25° rake angle. The natural diamond is oriented such that the top face of the diamond stone is a {100} plane and the cutting occur in the <110> direction relative to the stone. The synthetic diamond stone is oriented in the {100} plane with the cutting happening in the <100> direction. It is seen that, on average, the synthetic tool can cut approximately 38.5% longer distances without inducing significant brittle fracture on the surface.
This paper reports on the possibility of single point diamond turning (SPDT) of an axisymmetric convex aspherical fused silica lens. Due to the relatively abrupt tool wear during SPDT of fused silica, generally the process is not considered to be commercially acceptable. Surfaces created with SPDT are very rough and of no optical functionality. That said the SPDT can be a very convenient method in production of fused silica asphere and freeform optics should the process be amenable to producing relatively smooth surfaces. In this article it is shown that a lens fabricated via conventional fine grinding processes can be SPDT'ed to roughness values below 100 nm RMS and surface form better than 800 nm PV.
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