Surface Finish (Machined)

Surface finish is the texture quality of a machined surface, most commonly expressed as Ra (arithmetic average roughness) in microinches (µin) or micrometers (µm), with typical CNC milling producing Ra values of 32 to 125 microinches depending on tool geometry and cutting parameters. Engineering drawings specify surface finish requirements for critical surfaces such as bearing races, mating faces, or sealing surfaces where roughness would cause accelerated wear, leakage, or assembly problems.

Finer finishes (lower Ra values like 8-16 microinches) require slower feed rates, smaller chip loads, sharper tools, and proper coolant, increasing cycle time and cost, so programmers balance finish requirements with production efficiency. Tool geometry significantly influences achievable finish, ball nose end mills and corner-radius mills produce better finish than square end mills, and new sharp tools outperform worn tools dramatically.

In CNC machining, programmers often use a rough pass with aggressive feeds and speeds followed by a finish pass with optimized parameters, maximizing productivity while meeting all surface finish requirements.