Ra, the roughness average (or average roughness), is the average of the surface heights along a measurement trace. Sa is the average roughness over a measurement area. Can we calculate Sa by averaging the Ra of every trace across an areal measurement? The answer is: no. Here’s why. Calculating Ra As a refresher, to calculate … Read more
Some paint finishes are purposefully glossy or shiny. Others appear matte, or dull, or hazy. So, what leads to the difference…and what do all these terms really mean? Texture scatters light A perfectly smooth surface reflects light completely. If the light source is a collimated laser at 45 degrees incidence, it will reflect off the … Read more
I live in a world that is 1 mm x 1mm, and often less than 20µm high. It’s amazing, all of the physics that goes on in such a tiny area! Faced with a production or quality issue, people regularly send parts and want us to measure the entire part surface with our 3D optical … Read more
Rpc is the Peak Density in the X or Y direction of surface texture data. It is a measure of the number of peaks per unit length (i.e., peaks/mm) in the X or Y directions, respectively. In the ISO standards, the parameter is referred to as Rpc X or Rpc Y; however, in some software … Read more
Floyd Alburn Firestone was an acoustical physicist with wide-ranging talents, with important contributions in fields including acoustics, non-destructive testing, medicine, and surface texture. He is remembered as developing the first practical ultrasonic testing system, which is used widely for inspecting material fatigue in railroad cars, aircraft components, and other transportation vessels. The technique was also, … Read more
Rotary lip seals create a boundary around shafts in rotary equipment, typically to retain lubricant on one side versus air or gas on the other. On first consideration, it would make sense that a seal would act as a barrier, holding back all lubrication. In reality, however, when a sealing interface is working optimally, fluid … Read more
The Roughness Average, or average roughness parameter, Ra, is the average of the surface heights of every point along the “roughness profile.” Its equivalent for areal (3D) measurements is the Sa parameter. To see how Ra is affected by the cutoff, let’s start by taking a minute to define exactly what the roughness profile is. … Read more
Transmission clutch mechanisms and other complex systems require tight control of friction characteristics. Surface texture parameters such as Peak Heights, Valley Depths, Spacings and other bearing area related parameters (Spk, Sk, Svk) can be specified to control production processes and optimize friction characteristics. Michigan Metrology has been on the forefront of relating surface roughness to … Read more
Michigan Metrology – Surface Texture Measurement, Consulting, and Classes “I highly recommend your service.” – Aerospace Engineer Michigan Metrology provides surface roughness measurement, analysis, and training, to solve problems related to wear, surface finish, flatness, sealing, vibration, noise, and more. Our clients range from small, exciting start-up ventures to Fortune 500 companies in the automotive, … Read more
It’s a common intuition that smoother surface texture is “better” for sliding over another component. It seems natural that a smoother surface would wear less, have lower friction, and perhaps operate at lower temperatures. This gut reaction is widespread and runs deep. As an example, a few years ago a medical device was developed with … Read more