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Welcome to the Surface Roughness Analysis Blog

Why do brakes squeak? When will a gasket leak? What caused the haziness in my painted finish?

Surface texture and function are tightly linked. Understanding the relationship between texture and function, and sharing that information with engineers and quality professionals, is what Michigan Metrology is all about.

The articles in this blog explore the concepts of surface texture analysis and measurement. We show how you can apply these concepts to solve problems related to leaks, squeaks, appearance, wear, noise, fit, friction, vibration, adhesion, and many other functions.

Looking for more information on specific surface texture parameters? Visit our Surface Texture Parameters Glossary for an introduction to dozens of 3D surface roughness analysis parameters.

And, if you want to learn much more about surface texture consider attending our online and in-person classes for an immersive introduction to the many concepts in surface analysis.

Average Roughness Basics

Michigan Metrology - Average Roughness Basics - Article

How do I measure a Ra 32? or 32 Ra? or 32? The world of surface texture analysis can be deep and complex. By far, though, the most common surface texture callout on a print will be for Average Roughness, or Ra. So, what does Ra mean, how do you measure it, what information will it tell us about the surface, and maybe most compelling: what won’t it tell us?

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Multiscale Analysis in Action

Michigan Metrology - Multiscale Analysis - Article

As we regularly discuss in this blog, surface texture consists of a spectrum of spatial wavelengths. The term “multiscale spectral analysis” refers to the technique of analyzing the spatial wavelengths that make up surface texture.

When automobile manufacturers faced a vexing issue of non-matching paint finishes on body panels—even when the substrate steel met specifications—multiscale analysis proved to be the tool to unlock the mystery...

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When Wear Looks Like Filtering (and Vice Versa)

Michigan Metrology - When Wear Looks Like Filtering - Article

When a machined component leaves the factory its surface may have sharp peaks and crisp valleys from well-controlled machining processes. During the run-in period, peak material will wear and valleys will fill in with debris. Techniques such as filtering, and a number of surface texture parameters, can help us understand surfaces before and after wear, and even to predict how the surface will wear during run-in. ....

Using Ssc and Sds to Understand How Surfaces Interact and Wear

Michigan Metrology - Ssc Summit Curvature and Sds Summit Density parameters - Article

When surfaces move against each other in contact, we need to understand how the surfaces interact, how much friction is involved, and how they will wear in response to the contact.Two useful parameters in this endeavor are Sds (the Summit Density), which counts the number of summits per unit area of the surface, and Ssc (the Mean Summit Curvature) which is an indicator of the shape and size of the higher areas of a surface....

Making the Change from R Parameters to S Parameters

Michigan Metrology - R parameters and S parameters  - Article

Those working with 2-dimensional surface profiling will be familiar with the “R” family of surface texture parameters such as Ra (average roughness). Questions arise when we are faced with a new part, process or measurement instrument that instead call out areal (3D) S parameters. This post gives some background into these parameters and discusses important differences that may arise when transitioning from one set of parameters to the other...

Parameters Primer: ACF (Autocorrelation Function)

Michigan Metrology - Surface Finsih for Medical Devices - Article

The autocorrelation function (ACF) is a measure of how random or periodic a surface is. ACF is found by creating a duplicate of the surface, then shifting the duplicate relative to the original, in all directions. It is an excellent tool for finding periodic structure buried in texture data that could be the cause of noise, vibration, or excessive wear...


Applying the Areal Material Curve Parameters, Case Study: Analyzing Clutch Plates

Michigan Metrology - Surface Finsih for Medical Devices - Article

Spk, Sk and Svk, which are derived from the 3D Areal Material Curve, show the relationships between the peaks, core roughness, and valley regimes of a surface’s texture. In this example we show how these parameters can be applied—specifically, to control the real area of contact, fluid retention and other functions of a clutch mechanism's mating plates...


Surface Finish for Medical Devices

Michigan Metrology - Surface Finsih for Medical Devices - Article

Designing medical devices that function reliably and safely for decades requires careful attention to surface finish. From mirror finish surfaces for smooth fluid flow to very rough surfaces for bonding artificial joints to bone, understanding the aspects of texture that matter for each application is critical to long-term performance...


Parameters Primer: Rk, Rpk, Rvk (Stylus X,Y Parameters)

Michigan Metrology - Rk, Rpk, Rvk - Stylus X,Y Parameters - Article

The Stylus (X, Y) parameters (Rk, Rpk and Rvk) are derived from the Bearing Area Curve.They are helpful in understanding the real contact area of mating surfaces as they wear, for determining lubricant retention for engine components, ink retention for printing applications, and many other applications...


Nanometer-Scale Roughness

Michigan Metrology - Nanometer Roughness Article

“Nanometer-scale” surface roughness may seem rare and specialized. But, in fact, many components and common products require nanometer-scale, or sub-nanometer-scale, average roughness (Sa) in order to function. The ability to measure and control such roughness requires accurate metrology, and an understanding of how texture relates to a component’s intended function....


What Wear Measurement May—and May Not—Show You

Michigan Metrology - Wear Measurement Article

Accurately assessing how a component will wear is one of the most challenging aspects of product design. Daily, ongoing wear may be punctuated by periods of brief, intense stress or misuse. Accounting for as many of these effects as possible requires good data on how, and why, a component wears, as well as the understanding to interpret the data...


S Parameters Primer: Sds (Summit Density)

Michigan Metrology - Form, Waviness and Roughness Article

Sds, the Summit Density, is one of the “Hybrid” surface texture parameters. Sds counts the number of summits per unit area of the surface. It is a key parameter for controlling surfaces used in applications such as bearings, seals and electronic contacts, as well as painted finishes and other coatings...


Take a Hike! Defining Roughness, Waviness and Form

Michigan Metrology - Form, Waviness and Roughness Article

The terms "roughness," "waviness" and "form" are used everywhere in discussions of surfaces texture. But do we really understand how they are defined? We have to consider the application. It may help to think of the terms as they relate to a good hike, where "roughness" is the size of the rocks on the path, "waviness" is the rise and fall of the trail, and "form" is the shape of Picacho Peak...


Quality 101: Texture Measurements - Quality Magazine

Michigan Metrology - Form, Waviness and Roughness Article

...Modern metrology instruments, methods and surface texture parameters have made it possible to describe, in great detail, the functionally important features of a surface’s texture. A key aspect of surface texture is that it consists not just of random roughness but of many spatial wavelengths, or the peak-to-peak spacing along the profile or across the surface. The predomination of some wavelengths over others will determine whether a surface will glide or stick, retain lubricant or run dry, squeak or leak...

If you need less sliding friction, should you make the surface rougher or

Michigam Metrology - Sliding Friction Article

How does the surface texture affect the friction between two dry parallel sliding surfaces? The key understanding of the relationship of dry sliding friction to surface texture is linked to the notion of the "Real Area of Contact." Depending on the surface roughness and the material properties, the real area of contact
may not be too dependent on the surface roughness—in other words, if you make the surface "rougher" or "smoother" you may not affect the sliding friction. ...

Surface Texture Measurement – Ra, Rz, Rmax, Rz1max, Maximum Height

Michigan Metrology - Ra, Rz, Rmax, Rz1max, Maximum Height Article

This article discusses various surface texture parameters, their sensitivity to extreme peak/valley structures, and their utility for various types of surfaces and applications.




How Many Measurements?

Michigan Metrology - How many measurements for surface roughness measurement articleMultiple measurements made in different locations over a surface will generally demonstrate some variation in the texture parameter being assessed.

The question often arises: how many measurements do I need to make for a given parameter in order to obtain a particular level of confidence in the result? This article will give some basic guidelines for determining that number of measurements.

Surface Texture Measurement - Did You Set The Cutoff Lengths Properly?

Michigan Metrology - how to set cutoff lengths for surface roughness measurement article

...Along with specifying the surface roughness with Ra one must establish the cutoff lengths used to measure the surface. A specification of Ra alone is inadequate since measurement with different cutoff lengths may result in different measured Ra values.

Per the ASME B46.1-1995 standard, the long wave cutoff length must be specified on all drawings. Per ISO 1302-2002, both the long and short wave cutoff lengths must be specified...

Surface Texture Measurement — Rz...Which Rz?

Michigan Metrology - how to set cutoff lengths for surface roughness measurement article

When measuring surface texture, typically the average roughness, Ra is specified. The next popular parameter is Rz, which is more sensitive to extreme peak/valley structures. Since 1995, the ASME B46.1 standard has defined Rz as the average over the evaluation length of the successive values of the  peak to valley heights found per sampling length. Thus one may use any number of sampling lengths to determine Rz....


Patent Attorneys and Surface Texture

Michigan Metrology - how to set cutoff lengths for surface roughness measurement article

...Ensuring that the patent attorney understands "surface roughness" is the responsibility of the inventor.  For example, the inventor should make clear to the attorney that "surface roughness" may be defined as the average roughness, Ra or a number of other different texture parameters, measured with a particular spatial wavelength bandwidth.  Failing to emphasize the importance of specifying the spatial wavelength bandwidth to the attorney may result in a less effective patent than desired...

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