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What is a roughness tester?

Why we measure roughness

Surface roughness is an important parameter used to determine the suitability of a surface for a particular purpose. The irregularities on a machined surface impact the quality and performance of that surface and the performance of the end product. Rougher surfaces typically wear more quickly than smoother surfaces and are more vulnerable to corrosion and cracks, but they can also promote adhesion. A roughness tester, also referred to as roughness gauge or roughness meter, is a portable device that is used to quickly and easily measure the surface roughness (surface finish) of an object.

How we measure roughness

Typical roughness testers provide a linear roughness measurement, tracing a mechanical tip along a surface to measure roughness along an arbitrary line.  More sophisticated versions provide an areal roughness measurement, which measures an area of the surface using non-contact methods, such as lasers, optics, interferometers, and more, to give finer resolution and wide area measurements. For this discussion we will focus on portable roughness testers and linear roughness measurement.

surface roughness meter

Portable Surface Roughness Gauge

Roughness values are typically reported in Ra, which is the average absolute deviation from a central line of a surface; Rq, which is the root mean square of the deviation, and numerous other values that measure peak heights and depths of valleys. For most applications Ra and Rq provide an adequate indication.  For specially designed surfaces, the other parameters may be more appropriate.

Measuring different line lengths, shapes, offsets, and curves

Roughness testers can measure several predetermined lengths. Shorter distances are used to measure finer surfaces, while longer lines are traced for rougher surfaces.  It is good to ask about the different options available when considering a roughness tester.

Some roughness testers have an interchangeable stylus or probe for measuring different shapes, offsets, and curves. To measure either the inner diameter or an outer diameter, make sure the roughness meter under consideration can meet your requirements.

If you prefer either empirical or metric, some roughness testers are able to display the results of the surface finish in either micro-inches or micrometers, saving you the step of having to convert it manually.

Data storage options

Other options are the ability to store data on the device itself, and a computer interface through a USB port for data storage or further analysis using a computer.

More information

For more information on portable roughness testers, contact Ian at ian@microphotonics.com or (484) 274-9341.  If you would like to purchase a roughness tester, Ian can assist you so select the best option for your needs, or you can purchase directly from our online store.

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