Machinery's Handbook, 31st Edition
826 ISO Surface Finish Rules Determining Cut-off Wavelength: When the sampling length is specified on the drawing or in documentation, the cut-off wavelength l c is equal to the sample length. When no sampling length is specified, the cut-off wavelength is estimated using Table 3. Measurement of Roughness Parameters: For non-periodic roughness, the parameter Ra , Rz , Rz 1 max or RSm is first estimated using visual inspection, comparison to specimens, graphic analysis, etc. The sampling length is then selected from Table 3, based on the use of Ra , Rz , Rz 1 max or RSm . Then, with instrumentation, a representative sample is taken using the sampling length chosen above. The measured values are then compared to the ranges of values in Table 3 for the partic ular parameter. If the value is outside the range of values for the estimated sampling length, the measuring instrument is adjusted for the next higher or lower sampling length and the measurement repeated. If the final setting corresponds to Table 3, then both the sampling length setting and Ra , Rz , Rz 1 max or RSm values are correct and a representative measurement of the parameter can be taken. For periodic roughness, the parameter RSm is estimated graphically and the recom mended cut-off values selected using Table 3. If the value is outside the range of values for the estimated sampling length, the measuring instrument is adjusted for the next higher or lower sampling length and the measurement repeated. If the final setting corresponds to Table 3, then both the sampling length setting and RSm values are correct and a representa tive measurement of the parameter can be taken. Table 3. Sampling Lengths Curves for Non-periodic Profiles such as Ground Surfaces Curves for Periodic and Non-periodic Profiles
For Ra , Rq , Rsk , Rku , R D q
For Rz , Rv , Rp , Rc , Rt
For R -parameters and RSm
Rz , Rz 1 max , μm
RSm , μm
Ra , μm
(0.025) < Rz , Rz 1 max ≤ 0.1 0.013 < RSm ≤ 0.04 0.08 0.4
(0.006) < Ra ≤ 0.02
0.02 < Ra ≤ 0.1 0.1 < Ra ≤ 2 2 < Ra ≤ 10 10 < Ra ≤ 80
0.1 < Rz , Rz 1 max ≤ 0.5 0.5 < Rz , Rz 1 max ≤ 10 10 < Rz , Rz 1 max ≤ 50 50 < Rz , Rz 1 max ≤ 200
0.04 < RSm ≤ 0.13 0.25 1.25
0.8 4
0.13 < RSm ≤ 0.4 0.4 < RSm ≤ 1.3
2.5 12.5
8 40
1.3 < RSm ≤ 4
Table 4. Preferred Roughness Values and Roughness Grades
Roughness values, Ra
Roughness values, Ra
Previous Grade Number from ISO 1302
Previous Grade Number from ISO 1302
μm μin
μm μin
50 25
2000 1000
N12 N11 N10
0.8 0.4 0.2 0.1
32 16
N6 N5 N4 N3 N2 N1
12.5
500 250 125
8 4 2 1
6.3 3.2 1.6
N9 N8 N7
0.05
63
0.025
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