Measuring surface roughness

Three methods for measuring surface roughness on dressed lumber. 1998.

by Professor Gene Wengert

How can I measure surface roughness?

There are three ways to measure surface roughness that I have used. First, rub a piece of carbon paper gently across the surface. This will leave a dark color on the ridges. (For the youngsters who read this who only know about Xerox machines for making copies, you may have to ask an older person what carbon paper is.) Second, Look at the surface under low magnification--no greater than 100x, with 50x being better. A stereo microscope would be the easiest for me to use--with both eyes. Third, rub a little wax on the surface. Polish it up and then look for roughness. In fact, the glossier the surface, the more bumps you'll see.

Professor Gene Wengert is Extension Specialist in Wood Processing at the Department of Forestry, University of Wisconsin-Madison.

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Comment from contributor A:
True "measurement" of surface roughness requires a calibrated means of determining the peaks and valleys of the surface being evaluated. Those peaks and valleys can be measured using non-contact equipment, like lasers, or contact type tools that ride over the peaks and valleys. They then use the data collected from those tools to provide an answer of roughness. The roughness can be conveyed in micro-inches or micro-meters. The value given is also typically an average based on the distance of the area measured and the heights of the peaks and valleys. Typical surface areas are not 100% uniform, so the averaging is needed.