By examining roughness, waviness, or total profile separately, machinists can narrow the search for sources of error, and take effective action to reduce or eliminate them. Parameters The R a parameter measures average roughness. It is not sensitive to occasional spikes and gouges. On the other hand, the R max parameter is designed to detect these anomalies. The two surfaces shown here have nearly identical R a values but very different R max values.
Parameters are the quantitative methods used to describe and compare surface characteristics.
These are defined by the algorithms that are used to turn raw measurement data into a numerical value. Although more than 100 parameters exist, machinists have traditionally relied upon just one or two parameters. Currently, R a , or average roughness, is the parameter most widely specified and measured. The algorithm for R a calculates the average height of the entire surface, within the sampling length, from the mean line. Of more than a dozen roughness parameters specified by ASME in Standard B46.1-1995, two others that are widely used on the shop floor are R max and R z .