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"You must have heard of terms such as the Ra value when searching for a prototype or machined part. It is a complex term that refers to an industry standard used to specify what the surface roughness of a product design should or should not be. It is extremely important because it can directly affect the performance, functionality, and appearance of the final product. For instance, bearing surfaces must have a uniform pattern of roughness, which is necessary for retaining a film of lubrication. If the pattern of roughness is either too rough, too smooth, or uneven, the bearing will most likely fail.\n\nWhen it comes to calculating the Ra value, precision and accuracy matter. Note that there is a difference between surface texture and surface roughness. Surface texture is often used to determine surface roughness as explained below.\n\nHow Is Surface Texture Measured?\n\nSurface texture can be measured in several ways. The ideal option often depends on factors such as part material, size, or geometry. There is for instance, the probe or stylus method which is one of the most popular methods of measuring surface texture. The stylus of the probe used for measurement is known as a surfometer. It is gently drawn across the surface or face of a part. Even the slightest deviation from a reference or nominal line is recorded on a clear graph for analysis and interpretation. Surface roughness can then be calculated from the readings.\n\nOptical Photometry\n\nOnce the value of the surface texture has been calculated and used to determine the Ra value, photometry steps in. It is simply a way of looking at the total surface area of a part from a wider view to determine if there are other surface defects.\n\nOptical photometry is also handy when it comes to identifying asperities. These are inclusions, voids, and scratches that are sometimes found in raw materials. In other words, they are contaminants. Most mathematically derived models discount these anomalies as subtle and irrelevant. The presence of even a slight defect in critical applications, scientific instruments, or products from the aerospace/defense industry can prove to be catastrophic. That explains why the use of mathematically derived models to measure asperities is becoming increasingly unpopular. Precision and accuracy are everything when it comes to measuring surface roughness.\n\nDoes it Matter?\n\nYes, surface roughness matters if you not only want a perfect prototype but a perfect finished product as well. Remember that surface texture alone is one of the main areas where clients and factors disagree. That’s because it is often difficult to specify. That is why it is a good idea to first discuss this specific design aspect in detail just to clear doubts before commencing with a quotation or production. Keep in mind that there are many different and reliable ways to finish a surface, and to come up with appealing mechanical and aesthetic effects. With that in mind, explore all of your options before deciding on the best one."
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