Lesson 3 – Materials and Applications

What You Will Learn

Identify metals, crystals, and plastics that can be diamond turned
Compare common materials such as aluminum, copper, nickel, germanium, silicon, and plastics
Explain why some materials are better suited to grinding than diamond turning
Describe how material properties affect cutting behavior and process settings
Identify common SPDT applications in optics, molding, infrared systems, and precision manufacturing

Materials That Respond Well to Diamond Turning

Single point diamond turning can be used on a wide range of materials, including metals, infrared crystals, semiconductors, and polymers. Common examples include aluminum, copper, brass, nickel, germanium, silicon, zinc selenide, zinc sulfide, calcium fluoride, acrylic, polycarbonate, and polystyrene.

These materials are very different from one another, but each can produce a high-quality surface when the machining process is properly controlled. The tool geometry, feed rate, depth of cut, spindle speed, coolant, temperature, and workholding method may all need to change depending on the material being machined.

A material being considered diamond turnable does not mean that every grade, part shape, or setup will behave the same way. Material composition can affect chip formation and tool wear, while part geometry and mounting can affect vibration, distortion, and stability. For this reason, understanding the material is an important part of planning an SPDT operation.

Metals: Aluminum, Copper, and Nickel

Aluminum is one of the most common materials used in diamond turning because it machines well, is relatively lightweight, and can be used for both optical surfaces and precision structures. Aluminum mirrors are especially useful when the optical surface and the structure supporting it can be made from similar materials, because this can help the system respond more predictably to temperature changes.

Copper can also produce excellent diamond-turned surfaces, and it is commonly used for precision molds, replication masters, mirrors, and other components. Copper is softer and denser than aluminum, so its cutting behavior is different, but a properly controlled diamond-turning process can still generate a very smooth surface.

Nickel is often used as a plated layer rather than as the entire part. For example, electroless nickel can be applied over an aluminum or other metal substrate, which creates a hard surface that can then be diamond turned to the required optical form.

When a plated surface is machined, the operator must think about more than the cutting conditions. The thickness of the coating, its adhesion to the base material, and the stability of the material underneath it can all affect the finished surface.

Infrared and Crystalline Materials

Germanium, silicon, zinc selenide, zinc sulfide, calcium fluoride, and several other crystalline materials are important in optical manufacturing because they can be used at infrared wavelengths where ordinary visible-light glass may not perform well. Diamond turning can be used to produce precision surfaces directly on some of these materials, including spherical, aspheric, and other complex optical shapes. Germanium, for example, is commonly used for infrared lenses and windows, while silicon is used in infrared optics and other precision applications.

These materials do not behave like ductile metals. Many are brittle, so an incorrect cutting condition can produce cracking, chipping, pits, or subsurface damage instead of a clean surface. To reduce this risk, the process may use very small depths of cut, carefully selected feed rates, and specific diamond-tool geometry. Tool rake angle and edge condition can also become especially important, because the goal is to remove a very thin layer of material while limiting fracture. This means the material affects both the optical design and the machining plan. A material may provide excellent optical performance, but it may also require a much more controlled cutting process.

Plastics and Polymer Optics

Plastics such as acrylic, polycarbonate, and polystyrene can also be diamond turned. These materials are used for lenses, prototypes, optical components, contact-lens products, and molds because a sharp diamond tool can produce a smooth surface directly. Polymers are generally much softer than metals and crystals, but they introduce a different set of challenges. They can respond strongly to heat and clamping pressure, and they may bend or deform while they are being machined. For example, a plastic part may be clamped tightly enough that its shape changes slightly during the cut. The surface may appear correct while the part is held in the machine, but when the part is released, it can return toward its original shape and the finished optical form can change. Heat can cause similar problems because many polymers expand or soften more easily than metals. Good workholding, light cutting forces, and stable temperature conditions are therefore important when machining polymer optics.

Materials Better Suited to Ultra-Precision Grinding

Diamond turning is extremely capable, but it is not the best process for every material. Many optical glasses, hardened steels, tungsten carbide, and silicon carbide are usually better suited to ultra-precision grinding, polishing, or another manufacturing process. Some materials are simply too hard or brittle to cut efficiently with a diamond tool, while others can cause the diamond cutting edge to wear very quickly. Certain materials may also interact with diamond during machining, which can greatly reduce tool life.

Trying to diamond turn the wrong material can produce poor surface quality, excessive tool wear, cracking, or an unstable machining process. The important point is that ultra-precision manufacturing is not about using diamond turning for every part. The goal is to select the process that can produce the required form and surface finish while maintaining reasonable tool life and process stability. In some cases, the best approach may involve several processes. A part might be ground first to establish its general shape, then polished to improve the surface, while another material may be finished directly by diamond turning.
Materials & Applications Explorer

Materials & Applications Explorer

Select a raw precision-optics blank to see how its material behavior affects diamond turning, process choice, and common applications.

Select a material

Raw Material Blank

The image shows the material as a simple raw disc or puck, before the optical surface is generated.

Material Behavior

Cutting behavior

Heat sensitivity

Diamond tool wear risk

Why it behaves this way

What to watch

Key idea: The correct process depends on more than whether a material is technically diamond turnable. Material behavior, geometry, mounting, required surface finish, tool life, and process stability all influence whether SPDT, grinding, polishing, or a combined process is the best choice.

Applications Drive Material Choice

SPDT applications include infrared imaging optics, metal mirrors, contact lenses, lens molds, Fresnel lenses, diffractive surfaces, injection-mold tooling, optical scan components, electroform masters, fiber-optic components, and other precision products. The material is selected not only because it can be machined but also because it must meet the optical, mechanical, thermal, environmental, and production requirements of the finished part.

A successful process therefore begins by connecting application requirements to material behavior. The operator does not simply ask, “Can this material be diamond turned?” A more useful question is, “Can this specific material, in this geometry and mounting condition, be cut with the required form, finish, tool life, and stability?”

Single Point Diamond Turning 1 Section12 Lessons1 Quiz12 Weeks

Curriculum