258 TECHNICAL INFORMATION 1. Varieties of Surface Roughness Indicators Definitions and presentations of arithmetic average roughness (Ra), maximum height (Ry), 10 spot average roughness (Rz), average concave to convex distance (Sm), average distance between local peaks S and load length rate tp are given as parameters indicating the surface roughness of an industrial product. Surface roughness is the arithmetical average of values at randomly extracted spots on the surface of an object. [Centerline average roughness (Ra75) is defined in the supplements to JIS B 0031 and JIS B 0601.] QTypical calculations of surface roughness Reference Relation between Arithmetic Average Roughness (Ra) and Conventional Parameters Arithmetic Average Roughness Ra Some portion is extracted from the roughness curve in the direction of the reference line and by the reference length. This portion is presented in a new graph with the X axis extending in the same direction as the average line and the Y axis representing the magnitude. Ra is represented by the equation shown at right, in microns (μm). Maximum Height Ry Some portion is extracted from the roughness curve in the direction of the reference line and by the reference length. The gap between the peak line and the trough line is measured in the direction in which the magnitude axis extends, in microns (μm). Remarks: For Ry, find an area which has no extremely high peak or extremely low trough as the mark of flaw, and then extract the above reference length portion from this area. Ten-spot Average Roughness Rz Some portion is extracted from the roughness curve in the direction of the reference line and by the reference length. The average of the levels (Yp) of the highest peak to the fifth highest peak as measured from the average line and the average of the levels (Yp) of the lowest trough to the fifth lowest trough similarly measured in the said portion are added together. Rz is this sum, in microns (μm). Arithmetic Average Roughness Ra Maximum Height Ry Ten-spot Average Roughness Rz Reference Length of Ry (Rz) ℓ (mm) Conventional Finish Symbol Standard Series Cut-off Value c(mm) Graphical Representation of Surface Texture Standard Series 0.012 a 0.025 a 0.05 a 0.1 a 0.2 a 0.08 0.012 ~ 0.2 0.05 s 0.1 s 0.2 s 0.4 s 0.8 s 0.05 z 0.1 z 0.2 z 0.4 z 0.8 z 0.08 0.25 0.25 0.8 0.8 0.4 a 0.8 a 1.6 a 0.4 ~ 1.6 1.6 s 3.2 s 6.3 s 1.6 z 3.2 z 6.3 z 3.2 a 6.3 a 2.5 3.2 ~ 6.3 12.5 s 25 s 12.5 z 25 z 2.5 12.5 a 25 a 8 12.5 ~ 25 50 s 100 s 50 z 100 z 8 50 a 100 a 50 ~ 100 200 s 400 s 200 z 400 z ~ − − * Interrelations among the three types shown here are not precise, and are presented for convenience only. * Ra:The evaluation values of Ry and Rz are the cut-off value and the reference length each multiplied by five, respectively. Yp1, Yp2, Yp3, Yp4, Yp5 : Levels of the highest peak to the fifth highest peak in the said portion with the reference length ℓ. Yv1, Yv2, Yv3, Yv4, Yv5 : Levels of the lowest trough to the fifth lowest trough in the said portion with the reference length ℓ. X 0 Ra Y ℓ m Rp Ry=Rp+Rv m Rv Ry ℓ m 5 Yp Yp4 V5 Y 3 Yp Yp 2 YV4 YV3 YV2 1 V1 Y Yp ℓ Rz= Yp1 + Yp2 + Yp3 + Yp4 +Yp5 + Yv1 + Yv2 + Yv3 + Yv4 + Yv5 5 Ra = 1 ℓ f ( ) dx ℓ 0 GeneralTechnical Information Surface Roughness
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