To understand the 100 RMS Surface Finish, firstly we need to know something about RMS Surface Finish.When the surface roughness Ra of the workpiece is below 0.8 microns, it is called mirror surface.
About the meaning of RMS:
Viewpoint 1: It is an abbreviation for root mean square. In an optical article, it was clearly mentioned that the "root mean square roughness" of a part is: 0.996nm. So called Root Mean Square: The square root of the mean of the sum of the squares of a set of statistics, this roughness is actually Rq.
Viewpoint 2: Because the RMS system is an imperial unit, generally: RMS*25.4/1000=RA Example: RMS64=64*25.4/1000=RA1.6 Note: The unit behind RMS is microinch, (one microinch=, one Inch = 25.4*10mm, therefore, 1=25.4*10.) From the information found now, the conversion formula in point 2 is generally used in "foreign coating processing drawings", and the unit is mostly "micro-inch".
Viewpoint 3: RMS is equivalent to Rq. There is no fixed conversion relationship between Rq and Ra. Generally, the value of Rq/Ra is different according to different surface processing methods. (RMS40 is basically about Ra0.8um). Regarding the processing technology, there is an article saying: Usually, when the processing method of the metal surface is different, the ratio of Rq/Ra is also different. For example, the ratio of electric discharge machining is 1.24-1.27, the surface grinding is 1.22-1.27, the shotpeering is 1.24-1.28, and the lathe cutting is 1.17-1.26. ----- There are also related papers, journals and process drawings for this view. Such drawings are generally marked with surface processing methods.
Conclusion:
RMS and Ra are essentially two data processing methods in statistics, Ra is the average value, RMS is actually Rq, and the root mean square value is sought. These are actually two surface roughness representation methods, and the specific conversion should be comprehensively considered in terms of unit and processing technology. To decide what level of the surface finish, a surface roughness gauge is often used.
RMS 63 is a smooth surface finish, RMS 100 surface finish is an average manufacturing surface, RMS 25 is a very clean smooth surface finish.