Surface Finish Notes
Relevant Surface Roughness Standard:
BS 1134-1:1988 Title: Assessment of surface texture. Methods and instrumentation
EN ISO 3274:1998 Geometric product specifications (GPS). Surface texture. Profile method. Nominal characteristics of contact (stylus) instruments
EN ISO 4287:2000 Geometrical product specification (GPS). Surface texture. Profile method. Terms, definitions and surface texture parameters
EN ISO 4288:1998 Geometrical product specifications - Surface texture: profile method - Rules and procedures for assessment of surface texture.
EN ISO 1302:2002 Geometrical product specifications (GPS). Indication of surface texture in technical product documentation
Surface Texture
The accurate characterization of surface texture has become increasingly important in the instrument, computing, data storage, automotive and biomedical industries. Surface texture is a key consideration affecting the function and reliability engineering components.
The surface texture is the local deviations of a surface from its ideal shape e.g perfect flat shape, perfect cylindrical shape, spherical shape etc. The measure of the surface texture is generally determined in terms of its roughness, waviness and Form .
Roughness
The roughness of a manufactured surface generally results from the production process and not specifically from the machining process if any. The action of the cutting tool, chemical action, polishing, lapping, and the structure of the material all contribute to the roughness of the surface.
Waviness
Waviness, the more widely spaced repetitive deviations, usually relate to the characteristics of an individual machine or to external environmental factors. It may result from such factors as machine or work deflection, vibration, chatter, heat treatment, or warping strains. Because both process and machine induced irregularities occur simultaneously,roughness is superimposed over waviness.
Form
The form of a surface is the profile of the surface under consideration ignoring variations due to roughness and waviness. Deviations from the desired form result from clamping marks or sliding marks machining guide errors etc.
Sample Filtering
Modern surface texture measuring instruments record the stylus movement over the evaluation length electronically and can produce output readings to a significant level of detail. The instruments measure the roughness variations and the waviness variations . Selecting a roughness filter will remove waviness elements, leaving the roughness profile for evaluation. Selecting a waviness filter will remove roughness elements,leaving the waviness profile for evaluation. The signal filters operate on the digital information. Separating the roughness and waviness is achieved by using filter cut-offs.
lc = the long wave filter. In the roughness requirement this value is the sampling length. This value may be used as the basis for the Waviness surface texture indication
ls = the short wave filter used for the lower band of the roughness requirement.
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