Machinery's Handbook, 31st Edition
ISO Surface Finish Rules 825 ISO Profiles.— Profile parameters may be one of three types (ISO 4287). These include: R-profile: Defined as the evaluation length. The ISO default length l n consists of five sampling lengths l r , thus l n = 5 3 l r W-profile: This parameter indicates waviness. There is no default length. P-profile: Indicates the structure parameters. The default evaluation length is defined in ISO 4288: 1996. Rules for Comparing Measured Values to Specified Limits.— Max Rule: When a maximum requirement is specified for a surface finish parameter on a drawing (e.g. Rz 1.5max), none of the inspected values may extend beyond the upper limit over the entire surface. The term “max” must be added to the parametric symbol in the surface finish symbology on the drawing. 16%-Rule: When upper and lower limits are specified, no more than 16% of all measured values of the selected parameter within the evaluation length may exceed the upper limit. No more than 16% of all measured values of the selected parameter within the evaluation length may be less than the lower limit. Exceptions to the 16%-Rule: Where the measured values of roughness profiles being inspected follow a normal distribution, the 16%-rule may be overridden. This is allowed when greater than 16% of the measured values exceeds the upper limit, but the total rough ness profile conforms with the sum of the arithmetic mean and standard deviation (μ + s ). Effectively, this means that the greater the value of s , the further μ must be from the upper limit (see Fig. 7). 1
Upper limit of surface texture parameter
2
1
2
Fig. 7. Roughness Parameter Value Curves Showing Mean and Standard Deviation Indications of Transmission Band and Sampling Length in Textual Format: With the “16%-rule” transmission band as default it is shown textually and in drawings as: Ra 0.7 Rz1 3.3 If the “max-rule” transmission band is applied, it is shown textually and in drawings as: MRR Ra 0.7; Rz1 3.3
0.0025-0.8 / Rz 3.0
MRR 0.0025-0.8 / Rz 3.0
Transmission band and sampling length are specified when there is no default value. The transmission band is indicated with the cut-off value of the filters in millimeters separated by a hyphen (-) with the short-wave filter first and the long-wave filter second. Again, in textual format and on drawings: MRR 0.0025-0.8 / Rz 3.0 0.0025-0.8 / Rz 3.0 A specification may indicate one or both of the two transmission band filters. If only one is indicated, the hyphen is maintained to indicate whether the indication is the short- wave or the long-wave filter. 0.008– (short-wave filter indication) or –0.25 (long-wave filter indication)
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