Lapping

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Small Lapping Plate

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Logitech Lapping Machine Jig

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Lapping is a machining process in which two surfaces are rubbed together with an abrasive between them, by hand movement or using a machine. This can take two forms. The first form of lapping (traditionally called grinding) involves rubbing a brittle material such as glass against a surface such as iron or glass itself (also known as the "lap" or grinding tool) with an abrasive such as aluminum oxide, emery, silicon carbide, diamond, etc., in between them. The second form, called polishing, is to make a smooth and shiny surface by rubbing it or using a chemical action, leaving a surface with a significant specular reflection (still limited by the index of refraction of the material according to the Fresnel equations).

Process

In the lapping process, the abrasive is applied in a liquid or paste form to the lap or the workpiece. The lap is then used to work on the workpiece. The process is characterized by the use of a very fine abrasive particle dispersed in a liquid or paste form to remove material very slowly, which allows for a very precise finish and high degree of surface integrity.

Types of Lapping

There are several types of lapping, each suited to specific applications:

• Flat lapping, which involves lapping flat surfaces. It is often used to achieve extremely flat surfaces, to improve the surface finish, or to achieve a very tight tolerance.
• Cylindrical lapping, which is used for finishing cylindrical surfaces.
• Spherical lapping, for finishing spherical surfaces.
• Polishing, which refines the finish of the surface to a high degree of shine or smoothness.

Lapping Machines

Lapping machines come in various designs and sizes, depending on the type of lapping process and the size of the workpieces. They range from simple tabletop models to large floor-standing models. Lapping machines typically consist of one or more rotating tables (laps) and a conditioning ring or rings, which control the distribution of the abrasive.

Materials and Abrasives

The choice of material for the lap and the type of abrasive used in lapping are critical to the process. Common materials for laps include cast iron, copper, brass, and glass, while abrasives can include aluminum oxide, silicon carbide, diamond powder, and emery particles.

Applications

Lapping is used in a variety of applications, including the finishing of jewelry, optical lenses, semiconductors, mechanical seals, bearings, and hydraulic components. It is particularly valued in applications requiring very flat and smooth surfaces, or a high degree of dimensional accuracy.

Advantages and Disadvantages

The main advantage of lapping is its ability to produce very accurate, smooth, and flat surfaces, superior to those produced by other machining processes. However, it is a slow process that requires a high degree of skill and experience to achieve the desired results. Additionally, the process can be messy and requires the proper disposal of used abrasive materials.

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