Guide to: Flat-lapping and
fine-grinding machines

Flat-surface lapping and fine grinding are abrasive machining processes for generating extremely smooth, flat and parallel surfaces to precision thickness (flatness and parallelism to less than 50 millionths is possible with surface finishes below 8 micro-inches - see tables in magazine article) on workpieces of virtually any material: ferrous and nonferrous metals, ceramic, glass, carbon, and plastic. Stock removal is fast, workpieces are not subject to distortion from clamping or heat, expensive tooling is not required, and very thin or thick workpieces of regular or irregular shape can be processed.

the workpieces are cleansed of slurry compounds by rinsing. With one-side, or single-plate, machines, one workpiece surface is lapped per cycle, necessitating two cycles and workpiece turnover if both sides are to be lapped. With two-side, or dual-plate, machines, upper and lower plates lap both sides simultaneously. Many lapping machines are also suitable for polishing to still smoother, more reflective finishes.

Abrasives include aluminum oxide, silicon carbide, boron nitride and diamond of various grit sizes, depending on workpiece material and finish required. Aluminum oxide

In one-side lapping, a slurry of abrasive particles in oil or water is fed onto a rotating lower lap plate to form an abrasive film between the plate and the workpiece or a group of workpieces. The workpieces are held on carriers within one or more conditioning rings or gears to keep them from moving off the plate. As the plate and rings rotate and force is applied by weights or pressure plates, the workpieces are abraded to required thickness. After lapping,

is the usual choice for mild steels and nonferrous metals, the harder silicon carbide is often preferred for hardened steels, cast irons and ceramics. Lap plate materials include mild steel, hardened steel, cast iron, hardened cast iron and composites, that is, various reinforced resins. Anodized aluminum, stainless steel and other softer materials are often used for polishing. In general, the plate material chosen is softer than the workpiece material to keep the abrasive from embedding in or scratching the workpiece.