Surface roughness plays a very crucial role in determining how a product reacts to its environment. The finish of a product indicates the performance of its components. Also, the level of roughness may affect the effectiveness of a product.
This depends on the application of such a product. Engineers and manufacturers must maintain surface finish at all times. It helps to produce consistent processes and reliable products.
Surface measurements also help maintain control of manufacturing. It is very useful whenever there’s a need for surface engineering.
Different surface finishes have a variety of effects. The easiest way to get the desired surface finish is to compare it with the surface finish standards. Surface finish can help in the following ways and more:
To learn more about surface finishing, read our guide to plastic injection molding surface finish options and read our article about getting the best CNC machining surface finish for your products.
Surface roughness is a calculation of the relative smoothness of a surface’s profile. The numeric parameter – Ra – represents the average roughness. The Ra surface roughness chart shows the arithmetic average of surface heights measured across a surface.
As already mentioned, there are three basic components of a surface, roughness, waviness, and lay. Therefore, different factors are affecting the characteristics of surface geometry.
When you search for machining surface finish symbols on your favorite browser, you would notice a range of abbreviations. These include Ra, Rsk, Rq, Rku, Rz, and more. They are units used in measuring surface finish.
While most people refer to Ra as Center Line Average or Arithmetic Average, it is the average roughness between a roughness profile and the mean line. This is the most commonly used parameter for surface finish. The Ra surface roughness scale, often presented as a surface finish chart, shows typical Ra values used in engineering and manufacturing applications.
This roughness parameter is best used for anomalies such as burrs and scratches. It may not be obvious with the Ra surface finish chart though. However, Rmax is a lot more sensitive to those anomalies.
Unlike Ra, Rz measures the average values of the five largest differences between peaks and valleys. The measurement is done using five sampling lengths, and it helps to eliminate error since Ra is quite insensitive to some extremes.
In this section, you’ll find a table for the surface finish conversion chart. This table serves as a surface roughness comparison chart, helping you compare different roughness scales—such as Ra, Rz, and RMS—across various manufacturing standards and processes. Before diving into the chart, let’s go through some of the abbreviations you’ll encounter.
Ra = Roughness Average
RMS = Root Mean Square
CLA = Center Line Average
Rt = Roughness Total
N = New ISO (Grade) Scale Numbers
Cut-off Length = Length Required for Sample