Gaging Tip: Surface Texture from Ra to Rz

June 30th, 2010

The irregularity of a machined surface is the result of the machining process, including the choice of tool, feed and speed of the tool, machine geometry, and environmental conditions. This irregularity consists of high and low spots machined into a surface by the tool bit or a grinding wheel. These peaks and valleys can be measured, and used to define the condition and sometimes the performance of the surface. There are more than 100 ways to measure a surface and analyze the results, but the most common measurement of the mark made by the tool, or the surface texture, is the roughness measurement.

However, there are several different methods of roughness measurement in use today, and the method used on any given part depends largely on where in the world the part is manufactured, and the measurement parameters the manufacturer and the customer prefer to use. It is not uncommon for different parties involved in the production to use different methods for roughness measurement. In this article we will talk about only two of the many methods of roughness measurement, how to convert between these two methods, and how to avoid the problems caused by the inevitable use of more than one roughness measurement.

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