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Diamond turning, also known as single point diamond turning, originally referred to the process of producing mirror-quality surfaces on high-precision air-bearing lathes using an ultra-sharp natural diamond cutting tool.
The technique was largely developed in U.S. nuclear weapons laboratories, where components with extremely demanding tolerances in fit, form, and surface finish were required.
Over time, the technology was adopted by optics manufacturers, enabling the production of metal optical components with complex and highly precise aspheric geometries.
Over time, several approaches to diamond machining have evolved. At the core of all methods is the exceptional precision of the diamond turning machine, capable of positioning a tool with an uncertainty of less than 100 nanometers. The primary approaches include traditional turning, off-axis turning, fly-cutting, and free-form machining.
Traditional turning is an advanced form of classic lathe work. The workpiece is chucked on a lathe with an extremely accurate spindle and slides, while an ultra-sharp diamond tool with a precisely controlled nose radius machines the part. CNC interpolation of the X and Z axes enables the production of any rotationally symmetric geometry. In principle, it is equally straightforward to produce a parabolic surface for a reflecting telescope as it is to produce a simple cylindrical shape.
In off-axis turning, the workpiece is mounted asymmetrically to the spindle. This allows for simultaneous cutting of multiple parts or the creation of contours whose rotational center does not coincide with the part’s center. Certain optical configurations exploit this method to achieve complex geometries.
Fly-cutting and milling reverse the positions of the tool and workpiece: the tool is mounted to the spindle, and the workpiece moves on the slide. This setup enables the generation of flat, elliptical, or otherwise non-rotationally symmetric surfaces.
By adding additional axes of motion, diamond turning machines can produce completely free-form surfaces without any rotational symmetry. At this stage, the process resembles milling more than turning. High-speed grinding spindles can replace single-point diamond tools, allowing ceramics, glasses, and metals to be machined with similar precision. Grooves, gratings, and other complex surface features can also be created with this approach.
In principle, any material can be machined on a diamond turning machine. However, not all materials are suitable for single-point diamond cutting. The underlying theory, which depends on the electronic structure of the material, is complex.
As a general rule, most common non-ferrous metals, all plastics, and certain crystalline materials such as silicon and germanium can be diamond turned.
Materials that cannot be cut with a single-crystal diamond have alternative options: they can be plated with high-phosphorus electroless nickel, machined using cubic boron nitride (CBN) tools, or processed through grinding.
