If you work with precision surfaces, you’ve most likely encountered callouts for surface roughness/surface texture.
At first glance, roughness may seem straightforward…you run a roughness gage over a surface, it reports a number, and you make sure that the number is within spec. But there’s a LOT more to texture specification and measurement, and it can affect everything from sealing to friction, wear, appearance, noise…
In this series we’ll take you through the basics of surface roughness and how it’s defined, specified, measured, and analyzed. Along the way we’ll point you to additional resources that you can use to further your knowledge.
Want to take a deeper dive into these topics? Check out our Surface Roughness, Texture, and Tribology classes, on-line, and in person.
Now…on with the show!
#1: What is Surface Roughness?
When people talk about the roughness of precision surfaces, they often talk generally about the peaks, valleys, and other shapes that make up a surface. That’s essentially true…but in the world of precision surfaces, “roughness” has a more specific meaning.
Surface texture
All of those surface shapes taken together are most correctly called the “surface texture.” Think of a mountain that consists of peaks, ridges, ravines, etc. It’s also covered in pebbles, rocks, boulders, dirt… All of those shapes make up the shape of the mountain.
The texture of this mountain consists of the mountain itself plus boulders, rocks, pebbles, sand…
Roughness is part of surface texture
“Roughness” is a range of shape sizes within that total texture that we care about for an application. That’s important: what we call “roughness” depends on the application. There are no hard, fast dimensions that define roughness; we define the range for each application.
What we call “roughness” depends on the application.
Going back to the mountain, if the “application” is a hike, we may want to know some information about the pebbles and rocks along the path so we can wear the right shoes. If we’re driving a Jeep up the mountain, the pebbles and rocks won’t affect our ride. We need to focus on the boulders, dips, and crevasses. The size of the shapes that we call “roughness” will change with the application, and it’s up to us to define that range in order for “roughness” to be meaningful.
Watch our How Rough is Roughness? video to learn more.
In our next post in this series we’ll look at the other scales of shapes that are part of texture but may not be roughness. We’ll introduce the concept of “filtering” to isolate the features that we care about.