Surface metrology

It is important to many disciplines and is mostly known for the machining of precision parts and assemblies which contain mating surfaces or which must operate with high internal pressures.

Contact methods involve dragging a measurement stylus across the surface; these instruments are called profilometers.

Another disadvantage is that profilometers have difficulty detecting flaws of the same general size as the roughness of the surface.

For example, instruments that rely on optical interference cannot resolve features that are less than some fraction of the operating wavelength.

This limitation can make it difficult to accurately measure roughness even on common objects, since the interesting features may be well below the wavelength of light.

The roughness trace would be plotted on graph paper, and an experienced machinist decided what data to ignore and where to place the mean line.

Today, the measured data is stored on a computer, and analyzed using methods from signal analysis and statistics.

In the following some advantages and disadvantages to the main technologies are listed: The scale of the desired measurement will help decide which type of microscope will be used.

Another problem is that the stylus may be too blunt to reach the bottom of deep valleys and it may round the tips of sharp peaks.

The real surface geometry is so complicated that a finite number of parameters cannot provide a full description.

It is one of the most important topics when it comes to specifying and controlling surface attributes such as roughness, waviness, and form error.

Typically, either digital or analog filters are used to separate form error, waviness, and roughness resulting from a measurement.