surfacefinish

Surface finish, or surface texture, refers to the ensemble of small deviations on a manufactured surface relative to an ideal plane. It encompasses roughness, waviness, lay, and flaws, and is commonly characterized by roughness parameters such as Ra (arithmetical mean roughness) and Rz (mean peak-to-valley height). Measurements are performed with contact profilometers or non-contact optical methods, reported in micrometers (µm) or microinches (µin). Standards include ISO 4287/4288 and ASME B46.1.

Ra is a statistical average of departures from the nominal surface; lower Ra indicates a smoother surface. Waviness represents broader-spacing deviations from the nominal form, while lay describes the predominant direction of the surface pattern produced by tooling.

Factors affecting surface finish include material, cutting speed, feed rate, tool geometry, lubrication, and subsequent finishing operations. Common manufacturing processes that influence finish are turning, milling, grinding, honing, lapping, polishing, and shot peening. Finishing operations like bead blasting or buffing can increase or decrease roughness depending on parameters.

Applications: surface finish affects friction and wear, fatigue life, sealing performance, heat transfer, corrosion resistance, and mating accuracy. Smoother finishes reduce friction and gas leakage in seals; rougher finishes can improve adhesive bonding or coating adhesion. Tolerances for form, orientation, and finish interact with dimensional tolerances and cost.

In specification, the required Ra (and sometimes Rz or other parameters) is stated along with permissible tolerances, and the desired lay direction if relevant.