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Grinding, Sanding & Polishing
Surfaces are eroded by abrasive particles in these mechanical processes. The surface finish ranges from coarse to mirror, and can be a uniform texture or patterned depending on the technique used and type and size of abrasive particle. These processes can be used to finish plastic, metal, wood, ceramic and glass.
Bright and lustrous surfaces can be achieved with polishing. It is characterised by the use of compounds in the form of pastes, waxes and liquids in which the abrasive particles are suspended. Cloths are commonly used to apply the abrasive paste, either by hand or spun at high speed on a wheel. Depth of surface texture at this scale is measured as a value of Ra (roughness average). Approximate Ra values for metal are as follows: a ground finish obtained with 80–100 grit will be Ra 2.5 microns; a dull buffed finish from 180–220 grit will be Ra 1.25 microns; dull polish from 240 grit will be Ra 0.6 microns; and a bright polish produced with a polishing compound will be Ra 0.05 microns.