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Surface texture (finish) on precision machined parts is dependent upon three factors. First, the material specified must be able to produce the surface texture required. Second, the surface texture is dependent upon the tools and process used to produce the surface. Third, the surface texture specified should be consistent with the function of or use for the surface.
Ductile steels in the AISI 1000 series, 1018 as an example, do not lend themselves to or finer surface textures for surfaces produced on some machine tools, such as the automatic screw machine, although subsequent grinding or burnishing will produce finer surface textures. Surface textures to can be produced using the free machining AISI 1100 and 1200 series. Many grades of the nonferrous metals can be machined to produce surface textures in the range.
All surfaces requiring finishes produced by grinding, lapping or superfinishing techniques should be noted, and the final surface designated using ANSI/ASME B46.1, Surface Texture and ANSI/ASME Y14.36, Surface Texture Symbols. The digits shown in the surface texture symbol () indicate average surface texture. If a minimum or maximum average surface texture is required both values must be shown .
The finish should be consistent with the function of or use for the surfaces. Fine surface textures not required for component functionality are expensive. Specify fine, average or maximum surface textures only where required, and use a note to specify the minimum average surface texture for the remaining surfaces as shown in Drawing #4.
When a minimum surface finish is given, the result could be a more costly part; avoid this, if possible.
Define the exact location and average surface texture required by dimensioning the critical area or portion of a surface.
Always use the standard surface texture symbols as shown in ANSI/ASME Y14.36, Surface Texture Symbols, and ANSI/ASME B46.1, Surface Texture.