Glossary

Lapping is a precision finishing process used in manufacturing to achieve extremely flat, smooth, and accurate surfaces on a material. It involves rubbing two surfaces together with an abrasive slurry or compound between them. The abrasive particles—suspended in a liquid or paste—gradually cut away microscopic amounts of material, removing high spots and irregularities to create a fine, uniform finish.

In practice, lapping is often done with a hard tool or plate (commonly made of cast iron, copper, or glass) against the workpiece, with the abrasive medium applied in between. Unlike grinding or polishing, lapping removes material in a controlled, very slow manner, allowing for tolerances within millionths of an inch (microns) and surfaces with extremely low roughness values.

The process is commonly used in applications where exact fit, sealing, or optical clarity are essential. Examples include valve seats, gauges, bearing surfaces, optical lenses, and sealing faces in engines or pumps. Lapping ensures surfaces are not only flat but also free of burrs, waviness, or tool marks.

There are two main types: manual lapping, where parts are worked by hand against a lapping plate, and machine lapping, which uses powered lapping machines for higher precision and consistency. While lapping produces superior accuracy, it is relatively slow and usually reserved for finishing operations where conventional machining cannot meet the required tolerances.