Diamond turning is a process of mechanical machining of precision elements using Computer Numerical Control (CNC) lathes equipped with natural or synthetic diamond-tipped cutting elements. This process is also known as Single-Point Diamond Turning (SPDT). The process of diamond turning is widely used to manufacture high-quality aspheric optical elements from glass, crystals, metals, acrylic and other materials. Optical elements produced by the means of diamond turning are used in optical assemblies in telescopes, TV projectors, missile guidance systems, scientific research instruments, and numerous other systems and devices. A lathe is a common tool used in machining. ... A CNC Turning Center The abbreviation CNC stands for Computer(ized) Numerical(ly) Control(led), and refers specifically to the computer control of machine tools for the purpose of (repeatedly) manufacturing complex parts in metal as well as other materials, using a program written in a notation conforming to the... Conventional metalworking lathe In woodturning, metalworking, metal spinning, and glassworking, a lathe is a machine tool which spins a block of material so that when abrasive, cutting, or deformation tools are applied to the block, it can be shaped to produce an object which has rotational symmetry about an axis... For other uses, see Diamond (disambiguation). ... An aspheric lens or asphere is a lens whose surfaces have a profile that is neither a portion of a sphere nor of a circular cylinder. ... Structure of methyl methacrylate Polymethyl methacrylate (PMMA) or poly(methyl 2-methylpropanoate) is the synthetic polymer of methyl methacrylate. ... 50 cm refracting telescope at Nice Observatory. ... Braun HF 1, Germany, 1958. ...

Process

Diamond turning is a multi-stage process. Initial stages of machining are carried out using a series of CNC lathes of increasing accuracy. A diamond-tipped lathe is used in the final stages of the manufacturing process to achieve sub-nanometer level surface finishes and sub-micrometre form accuracies. The surface finish quality is measured as the peak-to-valley distance of the grooves left by the lathe. The form accuracy is measured as a mean deviation from the ideal target form. Quality of surface finish and form accuracy is monitored throughout the manufacturing process using such equipment as contact and laser profilometers, laser interferometers, optical and electron microscopes. A nanometre (American spelling: nanometer) is 1. ... A micrometre (American spelling: micrometer), symbol µm, is an SI unit of length. ... The absolute deviation of an element of a data set is the absolute difference between that element and a given point. ... A laboratory measuring equipment that uses a diamond stylus to measure a features length or depth, usually in the micron or nanometer level. ... Interferometry is the applied science of combining two or more input points of a particular data type, such as optical measurements, to form a greater picture based on the combination of the two sources. ... It has been suggested that microscopy be merged into this article or section. ... It has been suggested that Selected area diffraction be merged into this article or section. ...

The machine tool

For best possible quality natural diamonds are used as single-point cutting elements during the final stages of the machining process. A CNC SPDT lathe rests atop a high-quality granite base with micrometre surface finish quality. The granite base is placed on air suspension on a solid foundation, keeping its working surface strictly horizontal. The machine tool components are placed on top of the granite base and can be moved with high degree of accuracy using a high-pressure air cushion suspension. The machined element is attached to an air chuck using negative air pressure and is usually centered manually using a micrometer. The chuck itself is separated from the electric motor that spins it by another air suspension. Quarrying granite for the Mormon Temple, Utah Territory. ... A Chuck is a specialised type of clamp used to hold rotating tools or materials. ...

The cutting tool is moved with nanometre precision by a combination of electric motors and piezoelectric actuators. The motion of the tool is controlled by a list of coordinates generated by a computer directly from a CAD model. The final surface is achieved with a series of cutting passes of decreasing depth. Piezoelectricity is the ability of certain crystals to produce a voltage when subjected to mechanical stress. ... Computer-aided design (CAD) is the use of a wide range of computer-based tools that assist engineers, architects and other design professionals in their design activities. ...

Quality control

Despite all the automation involved in the diamond turning process, the human operator still plays the main role in achieving the final result. Quality control is a major part of the diamond turning process and is required after each stage of machining and, sometimes after each pass of the cutting tool. Even a minute error during any of the cutting stages would result in a defective part if it were not immediately detected. The extremely high requirements for quality of diamond-turned optics leave virtually no room for error.

The SPDT manufacturing process produces a relatively high percentage of defective parts, which must be discarded. As a result, the manufacturing costs are high compared to conventional polishing methods. Even with the relatively high volume of optical components manufactured using the SPDT process, this process cannot be classified as mass production, especially when compared with production of polished optics. Each diamond-turned optical element is manufactured on an individual basis with extensive manual labor.