Processing roughness of sanded wood surfaces

Any quantitative evaluation of a sanded surface requires that the data be filtered to remove form errors and waviness. Wood surfaces contain irregularities due to both the sanding process and the anatomy, so the anatomical roughness must be excluded from any measurement of the surface if the processing roughness is to be properly evaluated. The efficacy of a number of standard filters was examined to see if they were suitable for oak, beech and spruce surfaces sanded with P1000 grit. Filters in current standards introduced distortions, but a robust Gaussian filter, contained in a draft standard, appeared to give roughness profiles free of distortions. The processing roughness and anatomical roughness, contained in the filtered profile, were separated with an algorithm based on a threshold defined in the material ratio curve. Work is continuing to compare the properties of different grit size and species combinations.